AlllDE blbm?

NATL INST OF STANDARDS & TECH R.I.C

A11 102616417

Sleawarth J D/Vortex shedding flow met QC^OO U5753 NO.1302 1986 Vl98 C.1 NBS-P NBS TECHNICAL NOTE 1302

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Vortex Shedding Flow Meter

Performance at High Flow Velocities

J.D. Siegwarth

^-QC—

100

.U5753

No. 1302

1986

C.2
Tm he National Bureau of Standards was established by an act of Congress on March 3, 1901. The ^^ Bureau's overall goal is to strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a

basis for the nation's physical measurement system, (2) scientific and technological services for industry and

government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

The Bureau's technical work is performed by the National Measurement Laboratory, the National

Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials Science and Engineering

The National Measurement Laboratory

Provides the national system of physical and chemical measurement;

coordinates tfie system with measurement systems of other nations and

furnishes essential services leading to accurate and uniform physical and

chemical measurement throughout the Nation's scientific community, in- dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops,

produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

• Basic Standards^

• Radiation Research

• Chemical Physics

• Analytical Chemistry

The National Engineering Laboratory

Provides technology and technical services to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement

capabilities; provides engineering measurement traceability services; develops

test methods and proposes engineering standards and code changes; develops

and proposes new engineering practices; and develops and improves

mechanisms to transfer results of its research to the ultimate user. The

Laboratory consists of the following centers:

Applied Mathematics

Electronics and Electrical EngineeringManufacturing Engineering

Building Technology

Fire Research

Chemical EngineeringThe Institute for Computer Sciences and Technology

Conducts research and provides scientific and technical services to aid Federal agencies in the selation, acquisition, application, and use of computer technology to improve effectiveness and economy in Government

operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing

the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP

voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following centers:

• Programming Science and

Technology

• Computer Systems

Engineering

The Institute for Materials Science and Engineering

Conducts research and provides measurements, data, standards, reference

materials, quantitative understanding and other technical information fundamental to the processing, structure, properties and performance of materials; addresses the scientific basis for new advanced materials technologies; plans

research around cross-country scientific themes such as nondestructive

evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evaluation; and broadly disseminates generic technical information resulting from

its programs. The Institute consists of the following Divisions:

Ceramics

Fracture and Deformation ^ Polymers

Metallurgy

Reactor Radiation

'Hcadquaricrs and Laboratories ai Gaiihersburg, MD, unless otherwise noied; mailing address Gaiihersburg, MD 20899. -Some divisions within the center are located at [ioulder, CO 80303.

-'Located at Boulder, CO, with some elements at Gaiihersburg, MD.
NBS

RESEARCH

INFORMATION CENTER

Vortex Shedding Flow Meter Performance

at High Flow Velocities il%(.

J.D. Siegwarth

Chemical Engineering Science Division

Center for Cliemical Engineering

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

Sponsored by

NASA Marshall Space Flight Center

Huntsville, Alabama 35812

tr *

#^

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued October 1986
National Bureau of Standards Technical Note 1302

Natl. Bur. Stand. (U.S.), Tech Note 1302, 94 pages (Oct. 1986)

CODEN:NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1986

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
CONTENTS

Page

1. INTRODUCTION 1

2. THE VORTEX SHEDDING FLOWMETER 3

3. TEST FACILITIES 5

4. EXPERIMENTAL METHODS 8

5. FULL VANE METER DESIGNS 12

5.1 Meter Tests in a iy2-Inch Straight Duct 20

5.2 Meter Tests in a SSME LOX Duct 33

5.3 Vane Shape H3

5.'4 Double Cantilevered Vanes 55

6. CANTILEVERED VANE 63

7. RING VANES 70

8. AIR TEST RESULTS 7^

9. CONCLUSIONS 82

10. ACKNOWLEDGMENTS 84

11. REFERENCES 85

111

Vortex Shedding Flow Meter

Performance at High Flow Velocities

J.D. Siegwarth

In some of the ducts of the space shuttle main engines (SSME), the

maximum liquid oxygen flow velocities approach 10 times those at which liquid

flow measurements are normally made. The hydrogen gas flow velocities in

other ducts exceed the maximum for gas flow measurement by more than a factor

of 3. The results presented here show from water flow tests that vortex

shedding flow meters of the appropriate design can measure water flow to

velocities in excess of 55 m/s, which is a Reynolds number of about 2 x 10^.

Air flow tests have shown that the same meter can measure flow to a Reynolds

number of at least 22 x 10^. Vortex shedding meters were installed in two of

the SSME ducts and tested with water flow. Narrow spectrum lines were

obtained and the meter output frequencies were proportional to flow to ±0.5*

or better over the test range with no flow conditioning, even though the ducts

had multiple bends preceding the meter location. Meters with the shedding

elements only partially spanning the pipe and some meters with ring shaped

shedding elements were also tested.

Key words: air flow; cryogenicj flowmeter; hydrogen; liquid oxygen; vortex

shedding; water flow

V

1 . INTRODUCTION

Fuel and liquid oxygen (LOX) flows in rocket engine ducts have been

measured in the past using venturi flowmeters and more recently on the space

shuttle main engine (SSME) by turbine meters. The ducts are kept as short as

possible with the result that few straight sections of any length are

available to install meters. Both turbine meter and venturi meter

installations require extensive modification of the duct if added later. The

turbine meter also has the disadvantage of introducing moving parts into the

duct. The vortex shedding flowmeter was examined in this work as an

alternative to these meters for SSME duct measurements.

Conventional flowmeter installations call for 1 to 20 diameters of

straight pipe preceding a flowmeter of any kind and 2 to 4 diameters of

straight pipe after it [1]. If flow conditioning is introduced upstream of

the meter, 6 to 1 diameters of straight pipe between the conditioner and the

flow meter are still recommended. On the SSME, a straight duct section

exceeding 10 diameters is a luxury. Few if any of the ducts will permit a

flowmeter installation following recommended practice.

Other conditions exist in the SSME ducts that are not normally

encountered in conventional vortex shedding flowmeter applications. The flow

velocity of LOX can exceed 50 m/s , nearly 10 times the maximum flow for which

most commercially available flowmeters are designed. The fuel flow, hydrogen

gas in the case of the SSME, reaches velocities of 250 m/s, more than 3 times

the 76 m/s upper limit specified for commercially available flowmeters.

Flowmeters on the SSME are subjected to pressures as high as 55 MPa (8000 psi'

and to cryogenic temperatures. Though cryogenic vortex flowmeters are

available, the high operating pressure would probably require design

modifications
The National Aeronautics and Space Administration (NASA) requirements

call for a pressure loss at the highest LOX flow rate meter location not to

exceed 0.69 MPa (100 psi ) . This immediately makes a commercially designed

meter unacceptable since their pressure loss is 2.8 to 3.5 MPa (^00 to

500 psi) at the highest liquid flow rate. Also, to avoid extensive duct

modifications, NASA prefers that the flowmeter installs through their standard

11.2 mm diameter instrument ports on the ducts. This also means that the

meter must be able to measure flow without an upstream flow conditioner. If

the last two requirements can be met, the only modification of the duct

required to install a flowmeter would be the addition of one or two standard

SSME duct instrument ports in the appropriate place on the existing ducts.

To ascertain that vortex shedding flowmeters could be used under these

conditions, tests of flowmeters under simulated SSME duct conditions were

necessary. Since commercially available flowmeters cannot meet the AP

requirements, a suitable meter had to be designed. In addition, since

conventional flow is limited to much lower flow velocities, no known existing

liquid flow test and calibration facilities were suitable for testing meters.

An inexpensive water test facility was built near the National Bureau of

Standards (NBS) Boulder Laboratory to simulate LOX flow. Velocities equal to

or greater than those in the SSME ducts can be obtained in this test facility.

An existing air test facility was employed to simulate hydrogen flow. Air

densities corresponding to SSME duct hydrogen densities have been used for

these tests. The maximum hydrogen gas velocities could not be achieved

probably because air has a velocity of sound less than one fourth that of

hydrogen gas. The meter induces local supersonic velocities in the flow well

before the maximum hydrogen gas velocity is achieved.
2. THE VORTEX SHEDDING FLOVJMETER

Qualitative descriptions of the vortex shedding flowmeter have been

published [2-5]. Only a brief description will be given here.

A cylinder with its axis perpendicular to a uniform flow field whose flow

velocity exceeds a minimum value will alternately shed vortices off the sides

at nearly constant intervals forming the von Kkrmkn vortex street [6]. The

shedding frequency, f , of these vortices is given by

f = S I

, (1)

where V is the flow velocity and d is a characteristic dimension such as the

width, W, of the shedding cylinder in a direction perpendicular to both the

cylinder axis and the flow direction. The Strouhal number S can be nearly

constant over a wide range of flowrates depending on the cross sectional shape

of the shedding cylinder. The cylinder, often called a bluff body or shedder

bar, will be called a vane in this report. Equation (1) holds even when the

vane is placed across the diameter of a pipe when the pipe Reynolds number

exceeds lO"*. The vane partially blocks the pipe so the average flow velocity

by the vane increases as d increases. The quantities d and V in eq (1)

Interact so that there exists a value d for which the Strouhal constant is a

minimum. Commercial meters are designed to operate around this value of d.

The remaining requirement to create a flowmeter from a vortex shedding

element in a pipe is to provide a means to count the vortices shed per unit

time. Various techniques are used to convert the transverse flows or

transverse pressure pulses into a pulsed electrical signal. Thermal and

ultrasonic techniques have been employed to sense the time varying transverse

flows. Pressure sensors or strain detecting devices on the vane convert the

time varying transverse pressures generated by the transverse flow to an

electric signal pulse.
Though papers and brochures describing a particular meter abound, papers

detailing the experimental results that led to the choice of a particular

design are almost nonexistent. The bulk of the flowmeter development has been

done by meter manufacturers who keep this information proprietary. A few

papers do present some details of the factors considered in the selection of

the vane cross sectional shape or the vortex detection method [7-10].

Early studies of vortex shedding dealt mostly with shedding from circular

cylinders. Circular cylinders show a variable Strouhal constant in the 0.2 x

1 to 3.5 X 10^ Reynolds number range [11]. Later, it was noted that the

variable Strouhal constant in this range was a property of the circular

cylinder [12]. The few publications that show meter factor for commercial

meters as a function of Reynolds number show it to increase or decrease

rapidly [^,13] above a Reynolds number of about 2 x 10^. The decrease has

been attributed to cavitation of the test liquid. If the line pressure were

raised, cavitation should be suppressed so that some higher maximum Reynolds

number is achieved.

To determine whether a vortex shedding meter can measure flow at high

flow velocities it is necessary to demonstrate that vortices are shed from a

vane with a regular period that varies in a repeatable way over the flow range

of interest. If this is confirmed, additional factors must be considered in

the process of turning the vortex shedding phenomenon into a useful meter.

These are discussed below.

Since the meters used in the shuttle ducts will require calibration, the

Strouhal constant need not be constant provided it is single valued over the

range of interest and shows no rapid changes. Commercial meters, to reduce

the need for calibration, are usually designed to minimize any flow dependence

of the meter factor and sensitivity to fluid properties. A calibrated meter
need not have a Strouhal constant independent of whether gas or liquid is the

measured fluid.

Vortex shedding is not necessarily a stable process. Even when the

shedding frequency is relatively constant, the amplitude can vary to the

extent that some of the shedding events either do not occur or do not generate

a measurable signal if they do occur. The number of pulses lost at a given

flow rate is sufficiently constant that the meter performance is not degraded

because of it. Some commercial meter designs have successfully eliminated the

complete fade of the signal.

The mechanism that converts the vortex generated forces into an

electrical signal must be insensitive enough to other noise and vibrations in

the duct that the vortex generated signal magnitude is well above them. One

commercial meter examined had a power signal to noise ratio (S/N) of 30 to

MO dB with a noise peak well removed from the signal and 20 dB lower. The

requirements on S/N are quite dependent on the measuring electronics. A 20 to

40 dB S/N was considered sufficient in this work. A signal with a line width

at half amplitude less than 5% of the line frequency was considered adequate.

The flowmeter still must meet the requirement on pressure loss. The

pressure loss at maximum flow, as noted earlier, should be well under 0.7 MPa

(100 psid). Even though a commercially available meter greatly exceeds this

limit, a commercial meter was tested as a starting point for the work.

3. TEST FACILITIES

Existing water test facilities do not provide adequate pressure to

achieve the flowrates required to test to 50 m/s flow velocity. The static

head required to provide the flow velocity is about 1.4 MPa (200 psi ) . High

pressure water for the NBS Boulder test facility is obtained from the penstock
of a Pelton wheel driven hydroelectric plant. During the early testing at the

plant site, water at pressures up to 5.4 MPa (790 psi) was available. The

t6st facility has since been moved from the hydroplant to the City of Boulder

Betasso Water Treatment Plant. This location is at a higher altitude on the

same penstock. There only 3.9 MPa (570 psi) maximum pressure is available.

A drawing of the test facility is shown in figure 1 . A 1V2 in nominal

test section was selected for the initial tests to limit the pressure loss in

the 3 in nominal piping connecting the test facility to the penstock. The

remainder of the test facility piping is 4 in nominal. A ^4 in vortex shedding

flowmeter provides a measure of the average flow velocity in the test section.

This reference meter was calibrated up to about 5 m/s flow velocity. The

meter factor, for the present, has been assumed constant to about 10 m/s. A

iVj in meter by the same manufacturer compared to the 4 in meter showed linear

behavior to 30 m/s which was 5 m/s in the 4 in meter. This result suggests

the 4 in meter is linear to much higher flow velocities.

The M in flowmeter is placed ahead of the test section. The test section

is a straight section more than 25 diameters in length. Downstream of the

test section the pipe diverges to 4 in again. A 4 in globe flow control valve

is located just downstream of the diverging section. The test water exited at

ambient pressure back to the creek at the hydroplant but exits to the head

tank at the water treatment plant. The test piping configuration is

sufficiently flexible so that various SSME duct sections and other size ducts

can be substituted for the V/^ in straight test section. Flowmeters with bores

of 27.9 mm, 41 mm (iVj in nominal) 50.8 mm and 58.4 mm have been tested in this

facility.
c ;=»

' "-^/-vr4->

o

n

a*

O

4-5

(1) EbO
The pressure at the test meter decreases as the flow rate increases not

only because of pressure loss in the upstream piping but because of the head

lost achieving the velocity. Most of the flowmeters tested were to the limit

of the test facility.

The air test facility used for testing flowmeters at simulated H2 gas

densities is portrayed in figure 2. These tests were carried out at a local

gas flow test facility [14]. Their choked nozzle flow calibration meter

combined with pressure and temperature measurements at the test meter provided

the velocity calibration of the test meter.

As shown in figure 2, the test air passes through the test meter first

then through the choked nozzle serving as tFie flow calibration meter. The

upstream and downstream control valves are hand adjusted to keep a constant

pressure at the flowmeter while the flow is varied stepwise over the test

range. The choked nozzle exhausts to ambient and is sized to provide the

desired test flow range without exceeding about 2.7 MPa (400 psi ) at its inlet

side. Even though the control valves were manually operated, the change from

one flow rate to the next requires less than a minute.

Because pressures in excess of 7 MPa (1000 psi) are required in the test

section to simulate hydrogen fuel densities and because of the high flow

velocity requirements, mass flows up to 16 kg/s were required to do the tests.

4. EXPERIMENTAL METHODS

The measurements and measuring instruments evolved as the work

progressed so that information obtained in later tests was not always

aviiilable in earlier tests.
u

N

hiOz

(Do _ 3 O 03 —

Co

COD

D)

•*- Coo

(0o

Io>c

(D •o

CQ (U *^

tw

(V 0) 1- s « to l^^F o

4-> O

03 <M

CO

<DO

CNJ

<2> 5 °

CO U.

Q.
The original thermal detector in the reference flowmeter above velocities

of about 5 m/s became noisy and unusable. The thermal detector was removed

and a pair of pressure taps inserted in such a way that an external

differential pressure transducer could be connected between the two ends of

the cross port in the meter vane in place of the thermal sensor. The pulsed

pressure signal out of a variable-reluctance differential pressure transducer

was sufficiently noise free that it could be amplified and counted directly

with no other signal conditioning over the range of 10 to 75 Hz. The

frequency is counted to a precision of 0.1 Hz for most tests and estimated to

about 0.03 Hz. At low flows, the frequency was stable to better than 0.1 Hz

in a 10 s counting interval. At higher flowrates, the frequency is stable to

about ±0.1 Hz. Improvements were made to this detecting system that permitted

reference flow measurements eventually from about 5 to more than 80 Hz. This

range could be expanded from less than 1 Hz to more than 100 Hz by reading the

frequency with a Fast Fourier Transform (FFT) spectrum analyzer.

The output frequency signal from the test meter was fed to an amplifier,

then through an adjustable narrow band pass filter and to a counter for the

earliest tests. Later, a second amplifier and pulse shaper were added between

the filter and the counter. In recent testing, the FFT analyzer has been used

to measure the frequency, sometimes after the first amplifier and sometimes

directly.

An older model analyzer was used first to view the signal spectrum

qualitatively and measure the signal-to-noise power ratio (S/N). The FFT

analyzer made it possible to measure line width also.

The pressure loss introduced by the flowmeter was measured by a

differential pressure transducer connected between two pressure taps, located

10
about 3 diameters upstream and downstream of the meter. At first, this

pressure transducer had a 6.9 MPa (1000 psi) capacity and the line pressure

was used to calibrate it by switching the downstream tap to ambient pressure.

Later measurements were made with a 0.7 MPa (100 psi) range transducer

calibrated against a dial test gage. This transducer was more sensitive and

the installation permitted zeroing it at the operating pressure, which

eliminated a line pressure induced zero shift.

Swirl was introduced into the test section to test meter sensitivity to

it. Swirl was generated by four blades placed at 90° intervals around the

pipe on shafts whose axes lay along pipe diameters. The planes of the blades

could be angled with respect to the pipe center line. The design was after

Padmanabhan and Janik,^^ but strengthened considerably to withstand the higher

flowrates. External arms could be positioned from outside the duct to set and

provide a measure of the blade angle with respect to the pipe center line.

This generator withstood water velocities in excess of 50 m/s without failing.

Straight bladed turbine meters were used to measure the average axial

swirl. These were modified commercial turbine meters. The turbine blades

bent, then collapsed, at flows above 20 m/s. The collapse started by the

blades bending about halfway between the wall and the hub, suggesting that the

swirl measured was not well represented by an average swirl angle.

Measurement of average swirl in the V/^ in test section with the swirl meter

adjacent to the generator gave an average swirl angle that agreed with the

generator angles to about 1 or 2°. The difference increased slightly with

increasing flow. Eighteen diameters downstream, the measured swirl angle was

about 0.56 of the 6.i<° generator setting and 0.72 of the 25.6° generator

setting at flow velocities of about 6 m/s.

11
The flowmeters tested in swirl introduced by this generator showed

sensitivity to swirl in both the spectrum line shapes and magnitude of the

meter factor, as will be discussed later. Meters subjected to swirl generated

by elbows still showed sharp spectra. No measurements were made that

determined whether any alteration of the meter factor resulted from elbow

generated swirl. The swirl generator used by Padmanabhan and Janik^^ seemed

to perform satisfactorily. Their larger pipe diameter (4 in) and the lower

velocity (one tenth of that in this work), may account for the difference.

Apparently, the generator did not satisfactorily produce an elbow generated

swirl pattern for the tests reported here. The swirl sensitivities observed

in the test meters then were peculiar to swirl generator rather than swirl

generated by elbows.

5. FULL VANE METER DESIGNS

Commercial meters all use a cylinder for the vane, but the cross sections

vary considerably. Most of the designs have a flat face toward the oncoming

flow with sharp 90° corners to the sides. The width of this face is the

greatest width of the vane. The advantages of one design over another is

information not found in the literature. Whether any of these vane shapes are

satisfactory at higher flow rates could be determined only by flow tests.

Most of the shapes tested in this work are represented in figure 3- The

preponderance of those tested were rectangular in cross section. The

dimensions of the various vanes and the reasons for choosing them will be

discussed in Section 5. In parallel with the testing of the various vanes,

the vane suspension and vortex detection mechanism was developed.

The first flowmeters tested had pressure transducers sensing the

oscillating transverse pressure generated as the vortices shed. Because the

12
f! m^

Q> L

Q i n

LW

^5_

<b I! o I^^^

D)

•o

0)

0)

4->

Cl

toco

4-5 O

0)

CO

CO

(0oo

0) x:

jjtwo

4J

COo

5: i '-x"

"^

M •ot —

^ — o ^ o

u. :

0)

•--I

13
vane width had to be small to reduce pressure loss and because of the severe

environment, installation of an adequate pressure sensing detector on the vane

was not feasible. Attention turned to lift sensing methods of vortex

detection early in the testing. The time varying transverse pressures result

in a time varying transverse force on the vane. The resulting strain on the

vane is sensed at some point on the vane support exterior to the flow region.

The first "lift" design, shown in figure 4, was quite successful. The

mounting of the vane on one end was a flat spring with the thin dimension

perpendicular to the pipe axis. A strain gage was attached to this spring.

On the spring end, the transverse motion of the vane was restricted to 0.1 to

0.2 mm by the clearance between the vane and the body at the pipe wall.

This design has some undesirable features for a LOX environment. The

vane striking the wall could provide an ignition source. Also, the sharp

transitions along the one piece vane cause stress concentrations that result

in metal fatigue and failure of the vane.

Figure 5 shows the next successful meter design. The strain gage has

been replaced by a lead titanate zirconate (PZT) ferroelectric disc acting as

a strain sensor. The sensor was mounted outside the pipe and the strain in

the post was transmitted out through a dynamic "0" ring seal. Mounting the

sensor outside obviates the need for waterproofing it. The PZT disc produces

a strong signal with a much lower strain than that required by a conventional

metallic conductor strain gage so the post holding the vane was stiff enough

that no stop was required.

The figure 5 design includes another feature. This was the first link

vane. The end mountings of the vane are clevises with the clevis pins

14
Electrical

Leads

Strain Gage

Vane

Spring Section

Figure 4. A scale drawing of the spring vane design, the first that

produced a strong vortex signal.

15
Sensor

Drive Plunger

Fiberglass

PZT5A

Sensor

Sensor

Clamp

Screw

Yoke

Rubber Damper

Link

2.64 cm

Link Top

Mounting Post

Mounting Pin

Meter Body

Link Bottom

Mounting Plug

Figure 5. A scale drawing of the link vane design with a PZT strain

sensor.

16
parallel to the flow axis. This design removed the stress concentration at

the pipe wall and eliminated vane breakage provided that the vane was made of

materials with reasonably good strength.

Figure 6 shows an alternative design for the sensing head and fixed end

still using the PZT sensor and the link suspension. A vane and sensor

assembly of this design will fit through the 11.2 mm instrument ports of the

SSME ducts. The PZT sensor now detects the strain across a notch in the

mounting post. The signal from this design was comparable to that from the

figure 5 design.

The "0" ring seal on the drive pin must be eliminated for cryogenic

service. Figure 7 shows a cryogenic version of the figure 5 design and figure

8 is a cryogenic version of the figure 6 design. The sensor in both of these

designs is placed between two metal diaphragms at ambient pressure. The duct

pressure acts on the sides of the diaphragms opposite the sensor. The space

surrounding the PZT is filled with solid material, mostly metal, equal to the

PZT thickness to support the diaphragms against the duct pressure. One

conducting surface of the PZT is in contact with the diaphragm while the other

surface is insulated by three 0.1 mm thick layers of insulation. The center

sheet of insulation is slotted to accept a 3 mm wide by 0.1 mm thick

conducting strip which transmits the electrical signal to the outside of the

sensor body. The spacer material surrounding the sensor is a series of 0.4 mm

thick nested rings permitting some position adjustment of the sensor location

along the direction of the drive pin axis. A tube connects the two sides of

the sensor assembly to equalize the pressure across the assembly.

The clevis mounting of the vane has been retained on the sensor end. The

opposite end has been modified to a bayonet mount. This reduces the chances

17
PZT Strain

Sensor

Sensor Preload

Screw

Clamp Ring

Meter Body

Clevis Pins

Spring Washers

Bottom Plug

Cap

Figure 6. A scale drawing of the link vane design with an axial strain

sensor.

18
«

CO

Q)O>

i.

0)0)cOOoc

•o

t.

0)

<DE

0)

H-io

00 (1) c >

t- •D (1) 3

bO

19
of transmitting any pipe vibrational mode to the sensor. The axial drive is

probably the more sensitive to such a transmittal.

The axial drive sensing assembly shown in figure 8 has the sensor offset

from the axis of the duct ports. A more compact sensing head has been

realized by placing the PZT concentric to the axis of the ports and

introducing an offset into the drive pin. An even more compact arrangement

results when the sensor is offset and the pressure seal obtained by soldering,

brazing, or welding the diaphragm to the meter body. This seal need have

little strength. The strength of the seal is supplied by the bolts that hold

the two halves of the body together.

Tests have shown that no significant noise was introduced by pressure

fluctuations even though the sensor was subjected to the water test pressure

over its full surface. If pressure noise does become significant at the

higher SSME duct pressure, the figure 7 or side drive design offers a method

for the elimination of that noise. Another sensing head can be placed on the

opposite side and connected so in-phase signals cancel while the 1 80° out of

phase vortex generated signals add. This side drive design also should offer

the best isolation from pipe vibration.

5.1 Meter Tests in a W^-lnch Straight Duct

As a starting point, a iVj in nominal commercially available vortex

shedding flowmeter with a 12.7 mm wide vane, vane 1, which has a figure 3a

shape, was tested to high flow velocities in the water test facility of figure

1. Table 1 gives design details of those vanes discussed in this report. The

meter factor as a function of velocity is shown in figure 9. The Strouhal

20
Closure Plug

Sensor Tension

Adjust

Metal

Diaphragms

Drive Pin

Duct Port

Section

RD 261-3017 Seal

(typ)

PZT Sensor

Spacer

ane Bottom

Guide

Figure 8. A scale drawing of a design for cryogenic service with an axial drive sensor.

21
enC

o

•Hua

•H

i-J O

cn

0)

'Td

5-1 0)

4-1 QJ

CO H

£-

<D

4-> <yB

m^ C

f3 bO

•iH E m

0) Q) K TD

CO

0)bO

CDQ. 0)

CO bO

OO

c • CO O

> 2

oo

Q)>

03 Q) c

S-o

o

E

e

c»on

T3

t-- ^- c— o o

CM in LTi T— CM

O CM O O O o o o o

on

II T3

E OO

(U • CM o OO

II CO 5 CUh II 1

4-> co

en o L •o E

II (J-, CO E

CE cc 1

i

•o i i

o

II a: LO <u m ITi t^ • > • •

t

o ;- 1

O r ^ ^ ^

II II D II II -o •a o T3 o

1 o

1 o in <7^ 1

1 O <Ti OO

0^ CTi CTi MD =r

LTl in CM C— OO OO t—

in C7^0OC\J^L^l CM-=rC7NCM

LO

<^ <0 =T (T\ CM c— c^ OO in vr>

OO ^ -3- OO ^

vD <,0 vO LO >^

CM vo vo vo in

CO ^ '^ vo vri OO in c— t- i>- v£) CTi MD r—

<£) ^ ^ T- VD VO >sO '^o vo >x) in

• • » • • * t— in in in tr— t-- t~- t— t— t^ vO

CO CO XD CO J2 o -o j:> £1 X3 jo £1 n JO CO 0) J3 bO

T3

(0 O bO cfl -o

0) s*

Q.--- Q)

•-H D. CU CL, CO CO J CL CD >,

Nl H I3- ^ .=r -3" .=r J J J J J

T— >— CTn CJN CTv

:=r =r in in in J J 03 J

CTn C7> T— CTn in in in in

CQ J J J CQ CQ CD CQ CQ CD CQ

CT^ ^ ^ .- CTN C7> 0^ 0^ CT> CTn a^

in ^ JT ^ in in in in in in in

«- CO OO . in vr)t--cocrvO ^oooo.=r in vO t^ CO C7> o

CM ^ CM OO ^3- inCM 00 CM CM CO

22
CO

CD

0)bO

CD a

mCDex o

CO t, s: 3

CO bO

in

CO <^ ^ II

?B 5

E

CD o

CC II CC

bOC

CD

(DC

to >

x: x:

-p 4-> bO bO c C

CD CD .H —1 vO

<D CXD <D C <\J C

CO 1 CO > <£. >

in

II •o

I on

po CO C3D c» -3- m

O t- t^ C— LH CO CM

C\J r- r- ^ (M CM CM

LPi 0-) OO OO I f>^ I

I I I I

I CM I

I I

1 CM CM CM CM CM

T— .=r r— r— cT) m m .=T ijr> <o LOLOLOLnLn in LO LTi LO 1^ >~D VD VO

vo rn OO CO ::T -=r

t-- .=r .=r -=r ^o >sO

CM

:3-

vT) ^r> T— r— t— Lpi

>— ^ \r> LO \£)

LTi in t^ t-- t--

LPi v£) LPi LTi LTi f- C~- C~- >- C—

VO ^D vO vO

I>- t-- t~- C-- t^ in in LTi t~- D— in

•O TD O X3 TD n £> £1 n n jD jD JD JD -O £) JD -O T3 hO -O -O

CD e*

D.v_. (p O o c:) CJ> o •--< ca CQ CQ CQ cn Q Q Q Q Q CQ

D- <D >, C7^ C7^ C7^ CJ^ -- ,,

Cr^ C7^ C7^ N E- Lt^ LO m in •=r -=r :=r ITi in LTi 00

CDC • (0 o > 2 CM CM cx5cr>o >— CMon^Tin

CMCMPO poromoocY-)

o o o

Q CQ CD Q Q

C^ 0> C7^ O^ CT* in in in in in

^^ t— OO CT^ o ro ro ro on =r

o o o o

Q Q Q Q

C7^ CTv Cr> C7> in in in in

CM f>~) ^3" ST =T =T

C_) CJ o o o o '— ,— ^ T— CT> C7^

.=r .3- -3- ^3- in in

O T— CM ro .=r in

in in in in in in

o

C3> in

in

23
a

•H

!-i O

CO

(U

)-i 0)

4-1 CU

4Joo

CO H

COe

CD

CO

CD

<U

S_bO

0) am0)Cl CD W bO

•r-l

4-3 bOc

1—1

(DC

CO <D > oo

CM ^ 1 <

in JC x: x:

Jj ^ 4->

fv-) D.

a C2,

m CU (U QJ •a o •o

mo

II •o

CO

LPi CTi CTi

CNJ <- ,-

O

CNJ

OO ct

a

a =T y£> o o o . • ;3- on C-- ^ cr\ m

vD '>0 >X)

LTi LTi un O O Q

CO c^ c^

cr> ^ T- ^ (0

oj e*

D.'-^ QJ •^ a. o

a. CD >. CTN

SIH Lr>

cd tr cc

J

J

oo

in

tXD CT>O

in LO ^o ^ c\j oQ.

•ac

CD oX

•.-I <!-. co

4-3 CDco

>-, CD

CO

C

X3 CO>

«t CD bOC • •- •r-l jJ t. c

:3 * o cc s • « ^ •o c

•rH

L

I—1 > » J iH

•r-t .» 4-3

4-3

C c CO 3 o OE

<-i hO bO C C

•iH •rH s- CO cx

c/3 •> o» CO • •k • •. T3

S-o i> mc >

<Dm i-H

•r-l Q> 4J t c 3 CO n o

CO

t- I-H D- £>3 •1 o

Da

ate

24
V) *NX

o

o

Ld

26.0

25.0

24.0

23.0

22.0

21.0 -

20.0

O

o

o o®o

" o ooO°

o

AA

O O^ A A

iJ__l_^u^

0.0 10.0 20.0 30.0 40.0

AVERAGE VELOCITY, m/s

50.0

Figure 9 The meter factor as a function of velocity. Circles, a iVj in

commercial design meter, vane 1. Triangles, same meter body

with a vane half as wide, vane 2.

25
number can be obtained by multiplying the meter factor by the vane width in

meters from Table 1 for this and all subsequent plots. At the time of these

first tests the reference meter was not yet performing well and the counting

rate from it was read to only 0.5 Hz. At velocities above 25 m/s in the test

meter, the reference meter became too noisy to read correctly. Because the

pressure loss across the vane remained proportional to the flow velocity

squared to about 35 m/s, the meter factor probably remained constant to nearly

that flow velocity.

The vortex detector for this meter was a magnetic shuttle disc driven

back and forth by the pressure transmitted through ports from opposite sides

of the vane to opposite sides of the disc. This detector, made to detect

vortices in flows up to 7 m/s, was destroyed by the much higher flowrates.

Figure 10 shows why. The pressure loss, AP, across a meter should be

proportional to the square of the flow rate or velocity, V. The pressure

across vane 1 is 25 times larger at 35 m/s than 7 m/s and, since the

transverse pressure across the vane is proportional to the axial pressure

loss, the destruction of the detector is not surprising.

The pressure loss across vane 1 follows the AP versus V^ curve up to

about 38 m/s, where the pressure loss jumps well above the curve. This jump

probably signals the onset of cavitation at the vane. If the pressure in the

duct were high enough to suppress cavitation, the pressure loss would pass

close to the value estimated by the manufacturer of the meter shown by the

plus point in figure 10.

The pressure loss in the shuttle duct flow meters should not exceed 0.7

MPa (100 psi) which means the vane width must be reduced. The meter factor

for vane 2 is shown in figure 9. This vane also has the cross sectional shape

26
of figure 3a but is scaled down so that the width is 6.4 mm or half that of

vane 1 . The pressure loss was only about one fourth that of vane 1 , as shown

in figure 10. The meter factor, by the Strouhal relation, would be twice as

large as for vane 1. Instead, it is actually smaller than that of vane 1.

This means that the velocity past vane 1 is actually more than twice the

velocity past vane 2 because of the extent that vane 1 blocks the pipe.

The first method of obtaining a vortex generated signal from a 6.4 mm

wide vane was attempted with a pair of transverse oppositely directed ports

with a AP transducer connected between them. Though a vortex generated signal

was obtained, the S/N was poor. Next, a single port was provided in one side

of the vane and a high pressure transducer referenced to ambient pressure

served as a detector. Though this detection method worked somewhat better,

possibly because of the larger port, the S/N was still poor. In addition, the

pressure pulsations and the vibrations rather rapidly destroyed the

piezoresistive transducers used as detectors.

The transition from the vane cross section to the pipe walls is sharp in

commercial meters. The test vanes were made of brass for ease of machining

and were built with sharp transitions to the wall also. The forces on the

vane at the highest flow velocities was sufficient to fatigue and break the

vanes out. Though it has not been difficult to find designs that resist

fatigue, failure at the high flow velocities was not uncommon if special care

was not taken in the design to eliminate high stress concentrations.

Sensing vorticies via pressure ports did not provide a good S/N, probably

because of the rather long porting between the sensing location and the

pressure transducer and the small inlet area of the port. Furthermore,

strength requirements ruled against introducing even a miniature pressure

27
METER PRESSURE LOSS

5C10" 10' icf

D

7 10'

X

D

QQLdQ

10 -

5*10

7 ^

lrf

^

<

- 10

5*10° 10' itf

AVERAGE FLOW VELOCITY, m/s

Figure 10. Pressure drop as a function of flow velocity for vane 1,

circles, and vane 2, triangles.

28
sensor on the vane because the vane size is so small that the strength of the

vane could not be safely reduced by machining a recess for a sensor. Because

of this limitation, pressure sensing of the vortices was discarded in favor of

strain sensing.

Some meters of the design shown in figure 4 were constructed. Vane 3 was

a 6.M mm wide vane with the figure 3a cross section and vane 4 had the figure

3b cross section with W=D=6.1 mm. These vanes were tested before a spectrum

analyzer was used to examine the signal. However, the signal to noise ratio

was qualitatively quite high. The filter that had been narrow banded and

adjusted to follow the vortex generated signal could be wide banded to cover

the full flow range and not increase the counting rate by more than a few

counts over that obtained through a narrow band pass. The meter factor as a

function of velocity is shown in figure 11 for vane 4, which is the more

nearly linear meter of the two. The total scatter of these data is less than

]% in the nearly linear segment of the curve. Vane 3 was less linear than

vane 4, with the meter factor decreasing as the flow increased prior to the

sharp increase at 45 m/s.

This sharp increase in meter factor at the highest flow rates was

encountered in most tests. Though it has not been demonstrated unequivocally

that this is a cavitation phenomenon at the vane, the flow velocity at which

this sudden increase in meter factor occurs is dependent on line pressure.

The meter factor remained constant to a higher velocity at the hydroplant test

site than at the Betasso Treatment Plant test site where the pressure is

15 MPa (220 psi ) lower.

Hanging weights on the middle vanes 3 and 4 provided a calibration of the

output voltage as a function of transverse force. Assuming this transverse

29
V) *N

Ld

>

><:o

Ld

33.0

32.0

31.0

30.0

29.0

28.0

27.0

26.0

25.0 -

A

^ A ^

-7^^ T^ ^^T^

A

O O

O

O

o

CD)

o

o

o

o %^ o®

O _^ o —

g

o QiPcxr

24.0 ' I ' '

I I J—AiJi—^J-^-^- I I I I I I I I I I I I I Ii4-i^.»db. 0.0 10.0 20.0 30.0 40.0 50.0 60.0

AVERAGE VELOCITY, m/s

Figure 11. The circles show the meter factor of vane 4 as a function of

velocity. The triangles show the meter factor of vane 5.

30
force results from a uniform transverse pressure and dividing this force by

the transverse area of the vane gives a value for the transverse pressure.

The magnitude of this transverse pressure was between 3 and 4 times the axial

pressure drop to an estimated accuracy of 305t.

The first successful flow meter using a PZT sensor was vane 5. This

vane, made of beryllium copper, has since undergone several hours of testing

without failure, attesting to the superiority of the link vane over a single

piece vane and mount where fatigue resistance is concerned. Vane 5 was only

5.1 mm in width to further reduce AP. The meter factor of this vane increased

over that of vane U as shown in figure 1 1

The width was further reduced to 3.8 mm for vane 6. This vane vibrated

so violently that it was audible some distance from the pipe. This vane was

made of beryllium copper and did not break during the short test but

considerable wear occurred on the vane ends, clevis and clevis pins. The

meter factor was not constant. No further testing of full vanes less than 5.1

mm in width was done in the Ml mm ID meter size. For a 5.1 mm vane width, the

ratio of vane width to pipe diameter, W/Dp, is about 1/8. Most of the testing

has been carried out with vanes with W/Dp around this value.

A meter of a figure 5 design, with vane 5, was subjected to swirling flow

from the swirl generator. The meter was 18 diameters downstream and the

generator vane angles were 11.5, 15.3, and 19.2°. The meter factor decreased

with increased generator angle as shown in figure 12. The spectrum line

generated by the vortex shedding broadened and S/N decreased with increasing

generator angle. The swirl introduced by the generator did degrade the

flowmeter performance above generator angles of about 11°.

The figure 6 design meter was first tested with vane 7. This sensing

head and the slightly trapezoidal vane cross section was carried over from

31
o

LJ

a:

35.0

34.0

00^ 33.0 *NX

32.0

31.0

30.0

O

o

_a

A

-e- -e- o j^

A

O

T"

t

-^ X

+

X

-^f29.0

''''•'•''•'••••'•'••''••

0.0 10.0 20.0 30.0 40.0 50.0 60.0

AVERAGE VELOCITY, m/s

Figure 12. The effect of swirl on the meter factor of vane 5 as a function of the generator angle. Circles, 0°; triangles,

11.5°; pluses, 15.3° and X's, 19.2°.

32
cantilevered vane tests which are discussed in a later section. The meter

factor was essentially the same as obtained for vane 5, figure 11. The

spectrum lines, the first analyzed by a Fast Fourier Transform analyzer

(FFT),were comparable in width and S/N with those obtained from vane 5 in the

figure 5 design meter.

5.2 Meter Tests in a SSME LOX Duct

The highest flow velocity LOX duct on the SSME requiring a flowmeter is

the 58. M mm (2.3 in) ID Low Pressure Oxygen Turbo Pump drive duct or RS007035

(7035) duct. Prior to testing flowmeters in this duct, a straight test

section of this approximate ID (actually 59 mm) was built to establish that

the Ml mm ID test results could be scaled up to this larger duct size. This

test section was a single piece of pipe approximately 25 diameters in length

with a pair of diametrically opposed ports brazed to it 20 diameters from the

inlet end.

Tests with a vane assembly of a figure 6 design showed that Ml mm vane

results did scale up to the 59 mm size. Several rectangular shapes of

different dimensions were tested to better define an optimum vane width and

depth. Figure 13 shows the variation of the meter factor as a function of the

depth for vanes 8, 9, and 10, all rectangular vanes. These vanes were all

7.6 mm wide (W/Dp =0.129). As figure 13 shows, vane 9 with a depth to width

ratio (D/W) of 2/3 has the most constant meter factor over the flow range.

The vane with the most constant meter factor often produces the narrowest

spectrum lines and best S/N and shows the least signal fade. Figure IM shows

test results from vanes 9, 11, and 12 which all had D/W = 2/3 but different

widths. The meter factor of vane 9 was the most constant over the test range.

33
CO *N

>

o

LjJ

25.0

24.0

23.0

22.0

21.0

20.0

19.0

18.0

A

A

TT^ A A A A ^ ^ ^

-^^T^^ H-^^H X=^^ ' X' ^ +

4-

X

o 8o

o o

o

o

x;a—a^Q—

o

8

o o

^.^^^^^^

0.0 10.0 20.0 30.0 40.0

AVERAGE VELOCITY, m/s

Figure 13. The meter factor of a 59 mm bore meter for vanes of the same W but different D. Triangles, vane 8; plus and X, two tests

of vane 9; and circles and diamonds two tests of vane 10.

34
*NX

o

Ld

a:

26.0

25.0

24.0 -

23.0

> 22.0

21.0

20.0 -

+ -h T"

CbQQD O AO—30 QE

Q^ Q qQ

19.0 ^ Xv X X -^—X

y^—X—X18.0 ' i^K^UiiarfiMiifa 0.0 10.0 20.0 30.0 40.0

AVERAGE VELOCITY, m/s

Figure U. The meter factors of three vanes of different widths with

D/W=0.67. Pluses, vane 11; circles and triangles vane 9

(shown also in figure 13); and X, vane 12.

35
Figure 14 shows that the frequency, f, varies inversely with W as the Strouhal

equation suggests. It is not proportional, however, because the wider vanes

approach the minimum of S as a function of W. Figure 13 shows that the

shedding frequency is also inversely proportional to the vane depth D.

Figure 15 shows AP as a function of water flow velocity for a number of

vanes tested in 59 nm bore test section along with the pressure loss with no

vane installed. The pressure loss is around 0.25 MPa (37 psi) maximum at

30.5 m/s (100 ft/s). The maximum liquid velocity in the RS007035 duct to be

measured is presently 28 m/s (92 ft/s).

Figure 16 is a drawing showing the layout of the last half of the 7035

duct. The last three bends from the exit end forward are 35°, 30° and 60°

bends and in almost the same plane. The duct enters the plane of the figure

perpendicularly. Three 45° bends, then a 90° entrance bend, precede this

perpendicular bend. No more than two adjacent bends in the front end of the

duct are in the same plane. Out-of-plane bends can generate swirl which, if

sufficiently large, degrades the meter performance according to the results

obtained in the 41 mm ID tests, figure 12. The distortion of the flow by a

single elbow would also be expected to degrade the meter performance.

The first measurements of flow in the 7035 duct were done with a figure 6

design meter placed at the exit of the duct as illustrated in figure 16. This

meter consisted of an approximately 4 diameter long 58.6 mm ID meter body.

The vane in this meter was located about 3.7 diameters from the exit of the

final 35° bend. Spectrum lines from this flowmeter are shown in figure 17.

When the vane was perpendicular to the plane of figure 16, the top spectrum of

figure 17 was obtained. When the axis of the vane was parallel to the plane

of the bends, the much poorer spectrum line shown in the bottom of figure 17

was obtained. The variation of performance with orientation must result

36
METER PRESSURE LOSS

D

X

o

CL

LdQ

ct: Ld

I—

LJ

3^10

- Itf

Q.

<

10

AVERAGE FLOW VELOCITY, m/s

Figure 15. Pressure drop as a function of flow velocity for ^ari°"^

vanes in the 59 mm bore test section; pluses, vane 12; point

up triangles, vane 9; circles, vane 11; X's, vane 5^*; diamonds, vane 56; and point down triangles, pressure drop

between taps with no vane present.

37
Flowmeter

grc|^^/-Meter Ports

RS007035

LPOTP TURBINE

DRIVE

Figure 16. Diagram of the last approximately 1/3 of the RS007035 duct to

the space shuttle main engine. The location of an exit end

test meter and the pair of ports added for a meter

installation is shown.

38
START: Hz STOP: 800 Hz

u

PS<

H

.Jo

>

H

:=> H

o

START: Hz STOP: 800 Hz

Figure 17. Spectrum lines with vane 9 in the meter at the exit end of

the 7035 duct. Top, vane perpendicular to the plane of

bends. Bottom, vane parallel to the plane of bends.

39
from the flow distortion at bends. A similar result was reported by Cousins

et al. [7]. Distortion is much higher in the plane parallel to the bend than

it is in the plane perpendicular [16]. This result suggests that though the

average velocity on the two sides of the vane perpendicular to the plane may

differ, the velocity profile along the edge of the vane must be relatively

constant. The test results differed from the straight duct tests in that the

meter factor of vane 9 decreased with increasing flow while the meter factor

of vane 8 was constant.

Two opposite instrument ports were silver brazed to the duct at the

location shown in figure 16. This location was chosen as a result of the

tests of the meter at the duct exit. The axis of these ports is approximately

perpendicular to the planes of the preceding 60° bend and the succeeding 30°

bend. The ports were placed about two diameters ahead of the 30° bend. Not

only were sharp spectrum lines produced by a meter of the figure 6 design,

figure 18, but the power S/N exceeded 30 dB. The meter factor of vane 8 is

shown in figure 19. The total scatter from a constant value is less than

±0.5^ up to 32 m/s above which it increases sharply, probably because of

cavitation.

A swirl measurement at the exit of the 7035 duct with a straight bladed

turbine gave an average swirl angle of 2V2° . The 2V2 degree average swirl at

the duct exit could be two to three times higher at the meter location since

the swirl must decay from the meter ports to the end since no out-of-plane

bends are present between the meter and the exit to generate more swirl. The

spectrum lines, figure 18, were as narrow as any measured which suggests that

the swirl from the duct bends did not affect the meter. The swirl generator

producing this estimated 5 to 7° of swirl would certainly have broadened the

spectrum lines to a visible degree.

40
START: Hz STOP: 200 Hz

:;::::; '

^

o

:;:;:;:

w

%

w

M

J

H

>

' • • ' *

. *

:::;::;::p iniij

; \

:= I

'."^J \^

START: Hz STOP: 800 Hz

Figure 18. Spectrum lines of vane 8 in the meter ports on the 7035 duct,

Top, M.2 m/s flow velocity; bottom, 28.2 m/s flow velocity.

41
METER FACTOR OF VANES IN 7034 AND 7035 DUCTS

N

O

bJ

01

25.0

24.0

> 23.0

d

>

22.0

21.0

+

+

+

-=l=- + +

+ + + +

-=r H \- + ^+

A A o

^ ^ %^ ^ § ^ o oo

^^^1^^

0.0 10.0 20.0 30.0 40.0

AVERAGE VELOCITY, m/s

Figure 19. The circles and triangles show the meter factor of vane 8 in

the 7035 duct. The pluses show the meter factor of vane 13

in the 7034 duct. Both results are for water flow.

42
The bend configuration of the 7035 duct might have caused a cancellation

of most of the swirl at the meter location. A set of ports was brazed to

RS(507034 or Low Pressure Fuel Turbopump Drive duct in the location shown in

figure 20. The entrance bend of the duct is 30° followed by a 90° bend.

These bends are in the same plane except for a small offset at a couple of

welded joints. The plane of the 36y^° bend is canted at about 120° with the

plane of the first two elbows. The following 63 3/^° bend is in a plane

making a 25° angle with respect to the plane of the previous bend.

The meter factor of vane 13 in a meter of the figure 7 design installed

in this duct and water tested is shown in figure 19. Clean narrow spectrum

lines were again obtained, figure 21.

As figure 19 and the spectra of figures 18 and 21 show, the vortex

shedding flowmeter can measure flow in the shuttle ducts with no flow

straightening required. The meter performance for water flow in the 703^ and

7035 ducts was as good and probably better than the performance in long

straight ducts. The spectra of vane 13 were relatively clean up to 10 kHz as

shown in figure 22. Other than the small second harmonic (3 x f) at 825 Hz,

the other significant line was a broad line at about 3*3 kHz. This line is

30 dB down. It is probably a mechanical resonance since it is nearly

independent of flow rate. It is always seen and usually occurs somewhere

between 1 kHz and 5 kHz. The amplitude is generally 20 dB less than the

vortex signal.

5.3 Vane Shape

Because of the wide variety of vane cross sectional shapes found in

commercial meters, it is not obvious that an optimum vane shape exists for the

A3
RS007034

MCC COOLANT

Meter Ports

Figure 20. The RS00703M duct showing the location of the added flowmeter

ports.

A4
START: Hz STOP: 100 Hz

., ,., -»

:

: : ; : : ;

•

^

u

•

M

; H ;

§

::;;;; 1 ;

: /

I

[jl \.^K.

START: Hz STOP: 800 Hz

Figure 21. Spectra from vane 13 in the 703^ duct at water flow

velocities of 2.5 m/s (top) and 26.8 m/s (bottom).

45
>

M

O

PiW

o

START: Hz STOP: 10 kHz

Figure 22. Log spectrum of vane 13 in the 7034 duct from to 10 kHz,

46
commercial flow range. An optimum vane shape may exist for the narrower vane

at higher flows. Vane 4 was found to be inferior to vane 3 in terms of the

constancy of the meter factor. Rectangular shapes appeared to give somewhat

more constant meter factors so rectangular shapes were used in most of the

testing of ducts and sensing devices. Since some signal fade still occurred

and some variation of the meter factor with flow was found, some tests were

carried out looking for a more optimum shape.

Various manufacturers have commented that the corners between the front

face and sides of their vanes must be sharp. To test for corner effects, vane

14, with the same D/W ratio as vane 8, had the corners on one face of the vane

broken with a file such that the edge was beveled, though unevenly, at about

30° from the plane of the face to a depth of about 0.^ mm. The radii of the

other two corners were measured as 0.1 ± 0.05 mm. The difference in

performance between beveled and unbeveled front corners was evident after

testing the vane with the beveled face, then the unbeveled face, forward. The

meter factors for such a measurement are shown in figure 23. The average

meter factor was 6% higher when the flow was toward the beveled side.

Vane 15 was a vane similar in width to vane 14 but had a greater depth.

One face had sharp corners while the other face had the corners machine

beveled at 45° to a side depth of about 0.5 mm. The meter factors as a

function of velocity for this vane for the beveled edges forward and the sharp

edges forward are also shown in figure 23. The meter factor for vane 15 with

sharp corners forward was less than vane 14 because of the greater depth. The

meter factor with the beveled edges forward shows a sharp minimum around 9 m/s.

The average value of meter factor in the flat region is even higher, 125S,

relative to the flat face meter factor, than vane 14. The radii of the

47
25.0

24.0 -

in «N

o

23.0

O

22.0

21.0

O

O.o

o

o

X

13-

X ^ ^

xo

X

A X

A

A

X^ A A £^_^

X

X

+

+

-^ i.^ ±. + ^ I—=^^-^

0.0 10.0 20.0 30.0 40.0

AVERAGE VELOCITY, m/s

Figure 23. The effect of beveled corners on the meter factor.

Triangles, vane 14 with sharp corners forward; circles, vane

1^4 with rounded corners forward. Pluses, vane 15 with sharp

corners forward; X points, vane 15 with beveled corners

forward.

48
"sharp" corners were not measured for this vane but were probably as sharp as

vane 1^. No further measurements of corner effects have been carried out. A

minimum radius must exist below which the radius has no more effect on the

meter performance. This radius may be larger than 0.1 mm. Corner design

could prove to be a useful way to fine tune meter performance.

Some of the commercial meter vanes have values of D substantially larger

than W. Vanes with cross sections similar to two of these commercial designs,

vanes 15 and 17, were built and tested in the Hi mm size. Vane 16 with the

figure 3a cross section showed a meter factor decreasing by about 5% at 30 m/s

from the meter factor at 5 m/s. Vane 17, which had a cross section like

figure 3e gave a MO dB or better S/N but the meter factor decreased by more

than 5% in the 5 m/s to 30 m/s range. The vane was made of brass for ease of

machining and broke in half before the measurements were completed. Vane 18,

with its rectangular shape and D/W = 0.67, gave a fairly constant meter factor

for the 5 readings taken (see figure 3^).

The remaining cross section shape studies were done in the 4 diameter

long by 58.6 mm bore meter. They are vanes 19 through 29 in Table 1. The

sensing head of figure 7 was used for most of these tests. The link ends were

shimmed tight in the sensing head clevis.

Some of the reasons for choosing these particular designs were as

follows: the vanes of figure 3g and 3© cross section were designed to

eliminate possible effects of variation of the vortex detachment point should

that be causing fading. The cross section shown in figure 3d was designed to

reduce flow separation along the sides of the vane should flow separation

cause fading. Vanes 20, 21, 24, were similar to a commercial vane design.

The vanes shaped like figure 3c were similar to another commercial design.

49
None of the the vanes 19 through 29 were an improvement over the rectangular

vane cross section. The rectangular vanes of 7.6 mm width, a D/W of about

0.85 and with sharp corners, gave the narrowest spectrum lines, the best S/Ivl

and the least fade.

The test results suggesting the best signal properties from a vane with

D/W = 0.85 agree qualitatively with the results of Kalkhof [10] who shows

curves suggesting that the variation of the signal period would be minimum

around W/D = 0.85 for W/Dp = 0.125 at lower Reynolds numbers.

All of the 58.6 mm bore meter vanes tested showed varying increases in

meter factor at low flows. Some of the increase may be introduced by using

the head designs of figures 7 and 8. Some of this effect might also be the

result of the improved resolution obtained from changes in the method of

measuring meter frequency. The FFT spectrum analyzer was used to measure the

meter frequency for these tests rather than the counter. After the switch to

the bayonet for the end of the vane opposite of the sensor, shimming the link

end to remove all lost motion reduced the amount of increase of the meter

factor at low flow velocities.

One test was done to determine whether the clevis arrangement on the

sensor end might be causing some disturbance since the end of the clevis

penetrated slightly into the duct. A vane was made with a 3 mm thick disc at

the pipe wall and the sensing head was shimmed back 3 mm to place the inner

face of the disc slightly inside the pipe wall. This vane gave a meter factor

indistinguishable from a vane of the same W and D with no disc.

Though determining repeatability from measurement to measurement or vane

to vane of the same design was not the object of this work, some tests were

repeated. Vane 5 was tested both at the hydroplant test site and later at the

50
water treatment plant test site to determine whether the move affected the

meter factor. The magnitude of the meter factor at the two locations agreed

to'' about ^% in the flat part of the meter factor versus velocity curve. The

velocity at which the meter factor increased on the high flow rate end was

lowered because of the lower pressure at the treatment plant. In general,

vanes with the same W and D gave the same meter factor with minor variations

when the mountings were altered. Some of the variation in meter factor with

both vane and suspension design in the early 1.5 in bore tests were probably

caused by the gaskets used between the flanges and the wafer design meters. A

1 to 2 mm thick rubber gasket was used whose ID was around 1 cm larger than

the pipe bore. Later, it was found that these gaskets could still extrude

into the flow when the meter flange bolts were tightened. The extruded

gaskets can slightly constrict the flow in the vicinity of the vane. This

increases the flow velocity hence the measured frequency at that flow.

Three vanes with the same W and D, including vane 37 and 38, and one

identical to 38 but not included in the table, were tested in the 4 diameter

long 58.6 ram bore test section with the iron test section forming the inlet

duct. The meter factors were the same within the data scatter. Measurements

with the same vane but with different supports gave nearly the same values for

the meter factor.

One vane. No. 8, was tested in five different duct configurations. The

meter factor is shown in figure 24 for these tests. The approximately 0.6 mm

maximum differences in the meter bores are eliminated by plotting meter factor

as a function of the average velocity. The meter factor of the vane in the

five duct configurations varies by more than H%. The lower three curves in

figure 23 are in inverse relationship to the duct diameter. The likely

51
METER FACTOR OF A VANE IN DIFFERENT DUCTS

24.0

in «NX

23.0

O

Ld 22.0

21.0

O

^^

-Q

-^

V O

V V

"O" o o. o

o- o

-^ o

-V- -^ Vo

A O

-2r

O

A

U o O (9

o

o

A A

A

A

-+- _±.

A

X

tr-^ ^^ ^ Z)^rr^

+

-H-t

+

X

t + ^' + + +

0.0 10.0 20.0 30.0

AVERAGE VELOCITY, m/s

40.0

Figure 24. The effects of the duct on the meter factor of vane 8: Plus

and X points, the 7035 duct ports; point up triangles, at the

exit of the 7035 duct in a ^4 diameter long meter body;

circles; a straight single piece test section; diamonds, the

4 diameter meter body at the end of the straight test

section; and the point down triangles, the same as the

diamond points except that the flange on the end of the

straight test section has been bushed.

52
im

DRIVE PIN

PZT SENSOR

PRELOAD SCREW

SINGLE PIECE

FLANGE and VANE

SPACER

DIAPHRAGMS

Figure 25. Double cantilevered vane. The same vortex sensor shown in

figure 7 is used on the vane in this top port. This sensor

is not illustrated for simplicity.

53
explanation for the hierarchy of the these curves is probably not the duct

diameter but the wall roughness. The 7035 duct wall is probably the smoothest

so the boundary layer is thinnest and the center line velocity is lowest. The

4 diameter long meter at the end of the 7035 duct may have a rougher interior.

The interior roughness of the 7035 duct could not be measured for comparison.

The transition joints from this duct to the meter certainly contribute a wall

roughness. The iron test section has such a rough and uneven interior surface

that an accurate measurement of diameter was not obtainable. The wall

roughness would have to cause a 2% increase in the central flow velocity

between the iron duct and the 7035 duct to account for the observed

differences. For these three tests a figure 6 design sensing head was used.

The meter factors obtained for the upper two curves do not have a

convenient explanation. The 4 diameter long meter containing the vane is

downstream of the iron test section. This iron test section consisted of a

section of ZV^ in schedule 80 pipe to which schedule MO flanges were welded.

The ID of the flanges was about 5 mm greater than the bore of the test meter

body. After the top curve in figure 24 was obtained, the flange was bushed to

the meter ID, the flat gasket replaced by an ring, and the vane was retested.

The meter factor decreased about \%. The meter factor of two other vanes

showed only a small change or none at all when tested with and without the

bushing in the flange. The only differences between the earlier vane 8 tests

and these last two is the use of a head of the figure 7 design for sensing and

the use of the FFT to measure frequency. The FFT and the counter generally

gave the same frequencies when they were compared, leaving only the difference

in sensing heads or some as yet unknown peculiarity in the meter run to

explain the different meter factors.

54
The results shown in figure 24 demonstrate that the meter run contributes

significantly to the overall meter performance. Thus, a meter must be

calibrated in the duct in which it will be used for highest accuracy.

A few tests were done on a 28 mm (1.1 in) bore size meter. Though flow

dependent spectrum lines were obtained, the lines were generally inferior to

spectra obtained from iVj in meters. The vanes that gave the best results were

larger in cross section than a linear scale-down of the best V/^ in vane.

Further work is needed to find the best meter design for the 28 nm duct size.

To briefly summarize this section, the meters tested produced a vortex

generated output signal comparable to a commercial meter of similar size

except that the signal is subject to more fade. Since the few counts lost at

a given flowrate are small, no appreciable degradation of the meter

performance results. The contour of the corners of the front face had a

strong effect on the meter factor. Rectangular vanes with the pipe diameter

to vane width ratio of about 8 and a W/D of 0.85 gave the best results in the

58.6 mm bore meter while W/D = 0.65 was better in the 59 run duct. The vane

calibration was dependent on the duct as well as the average velocity. The

duct wall finish seems to be an important parameter. The meter factor is

probably independent of the vane mounting as long as the mounting is tight.

5.4 Double Cantilevered Vanes

Though meters with either a link mounted vane or bayonet mounted on one

end measured flow satisfactorily, the designs may prove unsafe for LOX duct

applications. The main concern is rubbing surfaces caused by expansion of the

duct under pressure and the distortion resulting from vibrations. A double

cantilevered vane design is illustrated in figure 25. This vane spans the

55
pipe but is formed by two bars cantilevered in from each side of the pipe that

almost touch in the middle. This design obviates the need for any mechanical

attachment across the pipe. Double cantilevered designs were first tested in

the ^^ mm diameter test section.

The tests of vane shape and head designs were carried out using link type

vanes to reduce the amount of machine work. A cantilevered vane and mounting

flange is best made from a single piece of metal which requires much more

machining.

The first test of the double cantilever design was vane 30. This vane

was formed of two aluminum cantilevered vanes of the same cross section, one

17.8 mm long the other 22.4 mm long in a 41 mm bore meter body. The

performance was similar to the vane 5 which it resembled but the meter factor

was about 5% lower. The main difference between vane 5 and 30 was the

slightly trapezoidal cross section of the latter.

The next test of the double cantilever, vane 31 , was carried out using a

pair of cantilevered vanes of the same cross section as vane 30 but with a

greater asymmetry in length. The longer of the pair was 28.5 mm but the

material was A- 286 stainless steel. The short opposite vane was still

aluminum. The meter factor was constant to within ±0.5$, and the S/N was

larger than 30 dB though the line widths were between 5 and 1% of the

frequency. The meter factor agreed well with a link vane of similar width.

This may be fortuitous since the meter run was a single section of stainless

steel pipe with ports rather than the wafer type used with the link vane

though the bores were supposedly the same. The pipe ID is uneven, which

precludes an accurate measurement. The only other 41 mm ID cantilevered pair

tested, vane 32, consisted of two rigid stainless steel vanes of equal length.

56
A pressure sensing port was provided on each vane but on opposite sides. A

hole up through the center of each vane communicated to opposite sides of a

differential pressure transducer. The spectrum lines obtained were 20 dB or

more above the noise but were dominated by the noise below about 250 Hz. This

noise was independent of the pressure transducer employed for the sensor. The

meter factor of this vane was about 30.3 Hz«s/m, about 3% lower than obtained

for vane 5, a link vane of similar dimensions. The meter factor increased

sharply below about 8 m/s and increased very slightly above. The scatter

about an average curve was about ±0.6$ above a flow of 8 m/s.

The first double cantilevered pair tested in the 58.6 mm size was vane 33

in the 4 diameter long test body. One vane was 33.5 mm long and made of A-286

stainless steel. A short aluminum vane completed the span of the vane across

the pipe. The meter factor appeared to decrease linearly with increasing

velocity giving an average value of about 21 Hz»s/m. The spectrum lines were

under 5% wide and the S/N was 30 dB or more. At the highest flowrate tested,

the meter frequency rather suddenly dropped as if something broke. No

breakage was evident. The cause of the sudden decrease is unknown.

Vane 3^ consisted of a pair of cantilevered vanes of equal length made of

stainless steel. These vanes were designed for cryogenic sensors which

required that the drive pin have an offset of about 4 mm so the sensor could

be mounted with its axis on the port axis. This double cantilevered square

cross section vane had a meter factor about ^.6% higher than vane 35, a link

vane with nearly the same dimensions, rather than lower as was found with some

of the ^^ mm bore double cantilevered designs.

The meter factors of vanes 36 and 37 which were 34 and 35 reduced in

depth to D/W = 0.85 still differed by U.6%. The meter factors, of course,

57
DOUBLE CATILEVERED VANE METER FACTOR

23.0

en *NX

UJ

>

22.0

O

UJ

a:

21.0

20.0

X

X V ^ \ XX >$< ^

-X

X X X X

o o

o 6 o o^ "^ ^

o

+

p Q^

+ +

+ +

0.0 10.0 20.0 30.0

AVERAGE VELOCITY, m/s

40.0

Figure 26. Comparison of meter factors of double cantilevered and link vanes of the same cross section. Circles show vane 37, the

only link vane. The other curves are all for double

cantilevered vanes. The plus points are vane 39, the X

points are vane MO, the triangle points are vane 36.

58
i

increased when D was reduced. The meter factors of vanes 35 and 37 are

compared in figure 26. The link vane, vane 37, was 0.1 mm wider, but link

vane 38 which had the same width as No. 36, also gave the same meter factor as

No. 37. The line widths were 3 to ^% for the three vanes and S/N was 30 to 40

dB.

The subsequent testing of double cantilevered vane 39 suggested a cause

of the discrepancy between the meter factors of vane 36 and 37. Vane 39A

consisted of the upper cantilevered vane of figure 25 but with a sensing head

on it like that in figure 7. The other half of the vane, 39B, is the

cantilevered vane shown in the lower port of figure 27 without the strain

sensor. The meter factor obtained is shown in figure 26. The meter factor of

this pair is almost the same as a link vane of the same dimensions. The meter

factor of the cantilevered vane is more constant than that of the link vane.

The No. 39 vane pair probably was mechanically stiffer than the No. 3^ and 36

vane pair.

Vane 40 consisted of a fixed half, No. 39B, and a sensing half consisting

of a modified half of vane 36. The modification is illustrated in figure 25

by the vane in the bottom port. The diaphragm seals of a meter of the figure

8 design have been eliminated by using a solder seal instead. A much more

compact sensing head is possible because the sensor can be set off center

within the port bolt pattern. Again, the meter factor was higher, figure 26,

though not quite as large as obtained with vane 36.

Three other double cantilevered vanes, 41, 42, and 43, were tested using

vane 39B as the vane opposite the sensing vane. The sensing half of the vane

pair consisted of a piezoelectric pressure sensor in the side for vane 41.

Vane 42 had a notched mount but with the notch depth no more than 4 inn rather

59
INSULATION

PRELOAD SCREW

PZT

STRAIN

SENSING

PINS

SPACER

(Not Required)

CANTILEVERED

VANES

BUSHING

PRELOAD

SCREW

Figure 27. Cantilevered vane designs that eliminate the diaphragm seal.

In the top port is vane ^^. In the lower is vane 39B with a strain sensor on the mounting flange.

60
i

than the typical 5.5 mm. Vane 43 consisted of a vane made of A-286 steel

whose front face width and depth were the same as 41 and 42 but the sides made

92° angles with the front face. These vanes all had nearly the same meter

factor as vane 36, figure 26.

The much lower meter factor obtained for vane 39 suggested that the

stiffness of the cantilevered vane support might contribute to the variability

of the meter factor. However, when the top vane in figure 27, 44A, was tested

opposite vane 39A, this pair, vane 44, produced a meter factor with the same

value as vane 41 , 42 and 43 rather than like vane 39 though the stiffness

should have been similar. Vane 44A was about 0.1 mm narrower than vane 39A

which could possibly account for the higher meter factor. Vane 45, consisting

of vane 39B and vane 44A had a meter factor intermediate between vane 44 and

vane 39. The spectrum line widths were only around 5% wide for vane 44 but

were more than 7% wide for vane 45 for unknown reasons.

All the parameters controlling the performance of these cantilevered

vanes cannot be discerned from this small number of samples. Apparently, the

mechanical stiffness of the vane mounting has some bearing on the behavior.

The performance of the double cantilevered vane seems much more sensitive to

suspension than does the performance of the link vane. The meter factor as a

function of flow velocity seems to be more constant for double cantilevered

vanes than for the link vanes in the meter run used for these tests.

Some significant variations of the signal spectra with vane suspension

occurred. Figure 28 compares spectra from vane 39 and vane 42 at three

similar flowrates. At the highest flowrate a number of lines appear in the

vane 42 spectrum. One of these lines is even larger than the vortex generated

line. At higher flows the extra lines faded again. All the double

61
>

M

o

w

ISo

START: Hz STOP: 10 kHz START: Hz STOP: 10 kHz

Figure 28. The three spectra on the left side are from vane 39 at

average flow velocities of 12.1, 23.5 and 36.2 m/s from top

to bottom. The three spectra on the right are for vane 42 at

average flow velocities of 11.1, 24.0 and 32.5 m/s, top to

bottom.

62
cantilevered vanes except 39 showed large spurious lines to some degree. The

meter factor did not change value when the extra lines appeared. This

suggests that the forces driving these modes may be something other than the

vortex shedding process.

Though the diaphragm system of figure 7 and 8 should provide a

satisfactory means of transmitting the vane strain to the detector, it is

nevertheless more desirable to remove the strain sensing mechanism entirely

from contact with the high pressure. The two sensing heads shown in figure 27

do this. The off-center PZT on the lower vane assembly senses the strain in

the mounting flange resulting from the vortex shedding forces. The drive pins

in the upper vane of the same figure are totally enclosed in the sensing head.

The sensor is attached by an axial threaded hole so the detector senses the

strain between the top flange and the end of the pin. Both these sensing

methods produced narrow spectrum lines. The lines were inferior to the best

obtained in that the signal amplitude was lower and the flow independent lines

in the 2 to 5 kHz region of the spectra were higher in amplitude relative to

the vortex generated line.

6. CANTILEVERED VANES

The cantilevered vane design has been discussed in section 5.5. The

basic design originated with an attempt to measure flow with just one

cantilevered vane inserted through one port and extending only partially

across the pipe. Besides the advantage of requiring only one instrument port,

the head loss due to the meter is reduced.

The concept was first tested by cutting off vanes 3 and 4. After

obtaining a velocity dependent signal from these two vanes, some cantilevered

63
vanes were designed using PZT discs for sensors. The first dozen showed a

poor to nonexistent vortex signal before a vane design was found that produced

an even passable signal. Vane 50 produced the first passable vortex signal

spectrum. The sensing mechanism consisted of a piston plunger in a hole down

the axis of the vane sensing the time varying pressure at a side port on the

vane. The piston acted against a PZT strain sensor.

Another 10 vane designs were tried before a successful design with a

strain sensing vortex detector was developed. An additional eight vanes were

tested before arriving at vane 51 . The dimensions of the vane giving the best

signal were, W = 5.1 mm, D = M.3 mm and L = 17.8 nm. After yet another eight

designs the figure 29 design evolved. This design fits through an SSME duct

instrument port.

Figure 30 shows the meter factor as a function of flow velocity for vane

51 and 52. The sensing mechanism of vane 51 consisted of two PZT sensors

measuring the strain introduced into the vane support and poled so the outputs

resulting from a transverse force on the vane added. A 19 mm diameter port

was necessary to install it. Vane 52 had the design shown in figure 29. The

meter factor of vane 52 is lower than 51 , probably because the vane mount is

stiffer. The meter factors differ from those of vane 7 which had close to the

same meter factor as vane 5, figure 11, even though the cross sections are

identical and the sensing head is similar. The meter factor of the

cantilevered vanes are flat to a much higher flowrate and is around 15$ lower

than the meter factor of vane 7. These differences stem from the same source;

the flow is partially bypassing the cantilevered vane. The drag introduced by

the vane causes the average flow velocity on the opposite side of the pipe to

be higher than on the vane side. The vane sees a velocity lower than the

64
Drive Pin

PZT Strain

Sensor

Clamp Ring

Vane

Figure 29. Illustration of a cantilevered vane that fits through an SSME

port.

65
*NX

>

o

Ld

28.0

27.0

26.0

25.0

24.0

+

TT^ L A

-4 :^

O

o

o

o

-O Cr Q P O O

o

oo

o

^^^^^^fa^^^^^ X^i^i^i^aJL^i^ ^^^

0.0 10.0 20.0 30.0 40.0 50.0 60.0

AVERAGE VELOCITY, m/s

Figure 30. Meter factor for vane 51 , triangles and pluses and vane 52

circles.

66
I

average velocity over the pipe at the same flowrate so the meter factor is

smaller. The upper limit the flowmeter can measure is assumed determined by

when cavitation occurs at the meter. Since the average flowrate is higher

than the flow by the vane, a higher average flowrate can be measured before

cavitation occurs.

Unfortunately, flow bypassing the end of the vane has negative aspects

also. Some spectra from one of better performing cantilevered vanes, vane 53

•

are shown in figure 31 • The line width is much wider and S/N much lower than

for link vanes with the same dimensions. Vanes of various shapes, such as

those of figure 3f and h, and various dimensions were tried to improve the

vortex signal to no avail.

The poor performance of the cantilevered vane in terms of line width and

S/N probably comes from a velocity gradient along the vane near the free end

caused by the bypassing flow. The gradient means that the shedding frequency

is varying from one part of the vane to the next. This is not conducive to

having a single shedding frequency and results in a broadened line. That the

single cantilevered vane works at all is more suprising than that it does not

work as well as a full vane.

Modifications such as adding a thin disc onto the bottom of the vane or

increasing D at the bottom were tried. The latter did not work at all. The

disc made no detectable difference which is not surprising because it was

small. A large one would not fit through the meter port. Any termination

structure at the free end of the vane should really be independent of the vane

and attached directly to the duct.

A pair of oppositely mounted 17.8 mm long cantilevered vanes were

installed in one test in the 41 mm bore duct. This left a 5.4 mm wide gap

67
START: Hz STOP: 500 Hz

START: Hz STOP: 1 kHz

Figure 31. Two spectra from cantilevered vane 53. at 5.2 m/s, top, and

20.0 m/s, bottom.

68
between the ends. This increased the meter factor (28 instead of 26 Hz s/m,

figure 30) as might be expected. The S/N ratio, however, was even poorer than

that obtained for a single vane, probably because the flow velocity gradient

at the end of the vanes was made even worse by the gap. This shows that the

gap between the ends of double cantilevered vanes must be small if the vane is

to perform like a link vane.

Vane 51 was tested under swirl conditions created by the swirl generator

used to test vane 5. The signal was already degraded at a 5° generator

setting and the meter factor reduced.

Even though the S/N ratio is markedly poorer and the line width is wider

for the cantilevered vane than the link vane, a cantilevered design meter such

as vane 52 or 53 could be usable in the iVj i'^ nominal size.

When the link vane designs were linearly scaled up from 41 mm to 59 mm

diameter duct, the test results were as good or better than those obtained

from the smaller diameter. Vanes 5^4 and 55 were scaled up versions of vane 52.

Vane 5^ was aluminum and scaled up linearly in cross section but was 3 mm

short of the scaled up length. Vane 55 was stainless steel and scaled-up

exactly. The vortex spectrum signal lines were wide and S/N was only about 15

dB. Vanes 56 and 57 retained the 5.1 mm width of the Ml mm ID meter but were

longer. The test results were no better than those obtained from 54 and 55.

Vane 56 was tested in the Ml mm meter and produced a S/N comparable to vane 52

even through it was longer. Vane 55 was subsequently tested in the meter at

the exit end of the 7035 duct. The S/N was even poorer at that location, less

than 10 dB and the signal line width was about 30? of the line frequency.

Because of the poor results obtained for the tests of the single

cantilevered vane in the 59 mm bore ducts, further testing of this design was

discontinued.

69
7. RING VANES

A ring shaped vane with the ring axis along the pipe axis sheds smoke

ring like vortices alternately off the inner and outer surfaces. This design

has been studied by more than one researcher, but the most extensive report in

the literature is that by Takamoto and Koniya [9]. Ring shaped vanes were

studied in this work briefly as a design that might be resistant to swirl.

The velocity component producing the axial swirl is parallel to the edge of

the vane and presumably would not affect the shedding from the ring. The ring

vane has one obvious disadvantage. Since the ring has no contact with the

wall, a support structure must be provided with its attendant flow disturbance,

The support structure should minimally perturb the flow, especially at the

front and sides of the ring. Adding a vortex detection mechanism compounds

the design difficulty.

The ring vortex meters tested were all IV2 in nominal meters. First, the

rings were mounted on the ends of three radial arms of 1/2 to 3/4 mm thick by

about 10 mm wide stainless steel plates with the large surfaces parallel to

the flow. The rings broke free from the arms in the first two tests. The

detector consisted of a 3 nim diameter tube inserted along a diameter to sense

transverse pressure. These tubes broke off as rapidly as the rings. On the

third try the ring of vane 58 was brazed to three stainless steel support arms

with about 40 mm length along the pipe axis. A thin metal reed with its

length along the flow direction and its width perpendicular to both the flow

and the pipe diameter was brazed to one of the support arms. A strain gage

placed on this vane gave an observable vortex signal but the reed broke off

the support as the flow was increased during the first test.

70
A second design, vane 59, was tried using 5 nm thick streamlined arms

instead of thin blades for support of the vane. A ring supported by two arms

with transverse pressure ports on the arms for sensing showed no vortex

generated spectrum line.

Vane 60 consisted of a streamlined support bar spanning the pipe with the

ring mounted ahead of it on two posts. The posts broke off on the first test.

The joints holding the second set of heavier posts broke but the ring stayed

in place and a good signal was obtained via a pressure port behind the center

of the ring that opened into the flow. The ring was brazed again to the posts

for a second test. This time the joints held, with the result that the meter

factor changed. The meter design is illustrated in figure 32. The meter

factors obtained with the support joints both loose and solid are shown in

Figure 33- The meter factor for the first measurement during which the ring

was loose from the supports was more constant with flow. A pressure port at

the same location that sensed transverse pressure was tried but no spectrum

line was seen.

The meter factor of this 11.8 mm ID by 16.4 mm OD ring is higher by a

factor of 2 than the 5.1 mm wide link vane. Tests with the swirl generator,

however, indicated a decrease of sensitivity with increasing swirl. No

further testing was done for three reasons: no apparent improvement to swirl

resistance was obtained, the vane would not insert through an 11.2 mm port,

and the problem of introducing a vortex sensing mechanism at these high flow

rates had not been satisfactorily solved.

71
RETAINING RING

STREAMLINED BAR

SHEDDING RING

FLOW

VORTEX SENSING PORT

Figure 32. The drawing shows vane 60. The shedding element is a ring.

The sensing port connected to a pressure tranducer exterior

to the meter.

72
RING VANE METER FACTOR

V) «NX

o

Cf

LJ

70.0

69.0 -

68.0 -

67.0 -

66.0 -

65.0 -

64.0 -

63.0 -

62.0 -

61.0 -

60.0

0.0 10.0 20.0 30.0 40.0

AVERAGE VELOCITY, m/s

50.0

Figure 33. Meter factor as a function of velocity for vane 60. Circles,

the first test with the ring loose. Triangles, the second

test with ring solid.

73
8. AIR TEST RESULTS

High pressure hydrogen gas density can be simulated by compressed air.

The compressibility and viscosity of compressed air differ from hydrogen, but

the most significant difference is the velocity of sound. The sound velocity

is 4 to 5 times higher in the hydrogen gas at the shuttle duct conditions than

for ambient air. The air tests can show whether gas flow at the duct

densities can be measured by the present meter designs. Air tests cannot be

expected to demonstrate the flowmeter performance at 250 m/s, wfiich is a Mach

number of about 0.7 in air but only about 0.2 in hydrogen. Local velocities

in the region of a slightly canted airfoil exceed Mach 1 in a free flow of

Mach 0.5, so the flow around a rectangular shape must certainly exceed Mach 1

at Mach numbers well below 0.5 [17].

Only the first vane. No. 61, was tested in air flow at the three

different hydrogen duct densities in which flow measurement is desired. These

densities were represented by air pressures of 8.36 MPa (1213 psia), 3.87 MPa

(562 psia), and 2.3 MPa (333 psia) respectively. The results of these tests

are shown in figure 3^ which shows the meter factor as a function of the

Reynolds number for the three tests. The meter factors at the three pressures

overlap up to velocities around 110 m/s, where the meter factors at the two

lower pressures increase steeply with Increasing flow velocity. This may be

the onset of localized supersonic flow. The 8.36 MPa measurements were only

carried to about 92 m/s, still below the transition velocity.

The X data points show the meter factor obtained for water flow

measurements. The meter factor for water was more than 10^ lower than for air.

Though many manufacturers of commercial meters design to eliminate the

sensitivity to fluid properties, the meter can be calibrated for the fluid to

be used.

74
LJ

COoe . n

n ^ a <D vO CO m 3

(U ro rH c on Q.

CO ^> •a "O 00 c o s

CO

(«-l •• ro ^-N

t. • •r-t V)c

<v c\j e 4->

COa

,g 3 CO C\J c vO ?^ t. LH E « -H ^—' • •O CO -^''-S. i-H CO -^ o -o Ou CO • C d) Z Q, 01 >> « Ld Q) CO t>- o-i m 05 Q) • C\J 2 *-i Q. C^O ^ 3 O 6

4-) CO CO

O Ou °o

009

ncti les, CO <0ro o 3 O •o • 0) CSD z •rt CO >

Ld

CO

O

CO

CO 4-> a> CO Qi CO • o. t.

4-J e -^

t- CO

O CO o <v o

4J J_> o o CO

n3 t. (U CO

<i-. <u .-1 CO +J CO 0)

S- CO c t.

OJ -5 ^ a.

4J CO E - S- o S X JJ o T • a-m o 0)

3)

Eb oi/s^H *n3A 'OAV/'OBdJ

75
The spectra were generally examined to 10 kHz since the vortex spectrum

line frequency will approach 10 kHz at flow rates of 250 m/s. Noise lines

occur mainly in the 5 to 8 kHz range, far enough above the vortex line that

the highest density hydrogen flow can be measured with existing designs. The

noise lines increase and decrease in magnitude as the flow varies. The

increase in magnitude did not appear to shift the vortex line even when the

line seems to be driven by a harmonic of the vortex frequency. Some of the

extra lines may be driven by the flow noise rather than by the vortex

shedding.

Vane 16, which has a triangular shape, gave the meter factor as a

function of Reynolds number shown in figure 35. The slope is opposite that

given by vane 61. The change of meter factor with velocity for water is

opposite that for air. Spectrum lines for vane 16 are shown in figure 36

where they are compared to those of vane 61 . The vortex generated lines of

vane 16 appear somewhat narrower than for vane 61 and fewer noise lines appear

below 5 kHz at the low flow rates. At higher flow rates, more noise lines

occur in the vane 16 spectra than obtained from vane 61. Also, a sharp

spectrum line is obtained to a higher flow rate for vane 16 than for vane 61.

Vane 5 was tested with air flow at 2.3 MPa. The spectra were noisy

though the vortex generated lines were sharp. The meter factor was not a

straight line and scattered above 75 m/s velocity.

One cantilevered vane was tested. The vortex spectrum line was small

relative to the attendant noise lines. The meter factor between 50 and

120 m/s was constant.

76
^

s

o

e

on

bJ

LJ

x:

4J m o

T3 x: -1 m

o

C 05

OS 60 o

"O

C ^ CO O O O -^ ^O C 4J o

<^< o

c

o

E

of

UJm

Z

00

eter

factor

as

a

functio

2.3

MPa

(333

psi).

The

e

16.

< OQ E C

o

4-> CO < <1) CO > < >-

4J «>0 <i-l ^ o

3

< LJ O <U 4-> x: c n

en CO <u < > 4J

(0 < <u s- 3 •HOC

<

O 0) L

<1

1 b J

35.

The

numb wate

w

t. q o o O O c3 3

Jo d CM

00

CM f^i u9M

00

^/s<rZH *n3A 'OAV/'OBdJ

77
STOPi 10 OOO

t 925 Hi Y. 641.2 •Vr-««

1

100 Vr»*

/DIV

Uv^ L,^JiAAA_^^-v^

STOPi 10 000 Hi

STARTi Hi

Xi 4250 Hi

S5. 4S5 Hz

245. 3 mVrmm

STOPi ID 000 Hi STARTi < 3500 Hi

85, 4B5 Hi

, 101 STOPi 10 OOO Hi

Figure 36. A comparison of spectra for vane 61 left column, to vane 16,

right column, at a pressure of 2.3 MPa (333 psi). Top left,

33.2 m/s; top right, 33.7 m/s. Second left, 71.6 m/s; second

right, 71.2 m/s. Third left, 97.5 m/s; third right

100.2 m/s. Bottom left, 121.1 m/s; bottom right, 123.3 m/s.

78
A second set of air flow tests were carried out on a 1.5 in meter. The

test section for these tests was a single 25 diameters long stainless steel

section with a brazed-on port block. Some vanes with a nominally triangular

cross section were tried because vane 16 performed the best in the first air

test. The depth of vane 62 was made less than vane 16 in an attempt to reduce

the increase of the meter factor with increasing flow velocity.

Vane 62 gave the meter factor versus velocity curve shown in figure 37.

The meter factor is not constant with flow and decreases more rapidly above

about 135 m/s. It was the same for the test at 2.3 MPa (333 psi) and 1.^16 MPa

(212 psi). The lower pressure is below any shuttle duct density but is near

the density capabilities of a NASA hydrogen flow facility. Because the same

calibration nozzle was used for both tests the lower pressure tests permitted

the higher velocities. The meter factor of the same vane for water is again

lower than that for air. At least one strong flow independent line appears

in most of the spectra of figure 38. The principal line remains in the 3.7 to

M kHz range and is dominated by the vortex line especially above about 100 m/s

flow. The presence of this line may cause the scatter at about 140 ms shown

in figure 37. In any case, a flow dependent line persisted up to a velocity

of about 180 m/s (590 ft/s), figure 38. The test results at the two gas

pressures overlap better when plotted as a function of velocity. In

contrast, the vane 61 meter factors at the three test pressures overlap better

when plotted as a function of Reynolds number.

The meters designed for liquid flow gave sharp spectrum lines in gas flow

even at densities less than 0.03 that of water. Noise lines approaching the

magnitude of the vortex lines were generated at various flows. These should

be reduced in magnitude if not eliminated completely for the meters to provide

flow measurement to 250 m/s.

79
DOUBLE CATILEVERED VANE TEST RESULTS

32.0

31.0 -

*NX

LJ

> 30.0 -

o

Ld

0<

29.0 -

28.0

0.0 50.0 100.0 150.0

AVERAGE VELOCITY, m/s

200.0

Figure 37. Meter factor of vane 62 as a function of velocity for:

pluses, water test data; circles, 2.3 MPa (333 psi) air; and

triangles 1.46 MPa (212 psi) air.

80
500

rnVrmi

Vrme

STARTi Hz

Xi 3575 Hz

BW. 95. 485 Hz

1 854. 1 BiVrmo STOPi 10 000 Hz START, Hz

Xi 4175 Hz

SWi 95. 485 Hz

1 450. 6 mVrme

STOP, 10 000 Hz

10 000 Hz START,

X, 5200 Hz

BWi 95. 485 Hz

Yi 349. 9 mVr-me 10 000 Hz

Figure 38. Some spectrum lines from vane 62 at air velocities, starting

on the left side; top, 79.9 m/s and 10^1 m/s; middle,

115.8 m/s and 13^.5 m/s; bottom, 152.7 m/s and 180 m/s.

81
9. CONCLUSIONS

A number of vortex shedding flowmeter designs were tested at high flow

velocities in a water flow test facility. The following conclusions can be

drawn from the results obtained for vanes consisting of a uniform cylinder

spanning the pipe:

1) A vane with a width 1/8 the pipe diameter can measure flow at

velocities up to 55 m/s with a maximum pressure loss less than 0.7 kPa

(100 psi). This loss is proportional to the flow velocity squared.

2) Up to a duct bore of 59 mm (2.3 in) some of the successful vane

designs tested can be installed in a diametrically opposite pair of the

standard 11.2 mm diameter SSME instrument ports.

3) The vanes mounted in the SSME ducts in straight sections as short as

six diameters in length can give sharp signal spectrum lines and a linear

response without any upstream flow conditioning. The vane should be mounted

with its axis perpendicular to the plane of the preceding bend.

4) A vane with a rectangular cross section and a ratio of depth to width

(D/W) between 0.6? to 0.85 seemed to give the best results in terms of

linear ity, signal fade, and signal-to-noise power ratio (S/N).

5) The sensitivity of one vane varied by H% depending on the meter body

and the pipe preceding the meter. This was probably caused in part by the

differences in the duct wall finishes.

6) The sensitivity could be varied over a range of at least 12% just by

the shape of the corners of the front face of a vane with a rectangular cross

section.

Air at the density of the hydrogen gas in the SSME ducts was used to test

a few of the meters designed for and tested in water. The following general

results were obtained:

82
1) The meters designed for water sensed gas flow to densities of 0.025

that of water.

2) A vortex line was obtained to a velocity of 180 m/s (590 ft/s) for

one vane. The much lower velocity of sound for air probably limited the

velocity.

3) A triangular cross section appears to produce superior spectrum

lines when measuring gas flow.

k) The meter factor in Hz«s/m for air was found to be slightly larger

than for water for the vanes tested.

5) The highest Reynolds number attained was 22 x 10®. This is about

twice that of the LOX flow in any of the SSME ducts so no Reynolds number

limit should be encountered for LOX flow.

6) Some other lines, probably some mechanical resonances, approach the

magnitude of the vortex signal in the air test spectra and should be

eliminated.

Vanes partially spanning the pipe and cantilevered from one side possibly

performed well enough to be used as meters in the 1^4 in nominal size only. A

vane consisting of a ring placed with its axis parallel to and centered in the

pipe also produced a flow dependent spectrum line up to velocities of ^0 m/s.

The problems of mounting the ring and detecting the vortices generated in the

severe flow environment do not make the ring design particularly attractive.

As long as the link vanes tightly fit the support on the ends, the design

of the support seemed to have little effect on the meter factor for a single

piece vane spanning the pipe and mechanically attached to both supports.

Link vanes of the same dimension gave the same meter factor. This was

not true for double cantilevered vanes. The meter factor seemed to increase

83
as the stiffness of the mount decreased. Only one pair of oantilevered vanes

gave nearly the same meter factor as a single piece vane of the same

dimensions. It was not clear that these were stiffer than the others.

Because of the small cross section of the vane and mounting port, vane

movement probably affects all these vanes regardless of design.

Most of the testing was done using a sensing mechanism that transmits

mechanical motion through a seal. This seal has been eliminated by a design

that measures the strain in the vane structure without penetrating into the

high pressure interior of the duct. So far, the S/N was poorer for this

detector than the detectors that penetrate into the duct, but some additional

development could eliminate this difference.

In general, the vortex flowmeter designs tested would measure water flows

to velocities greater than 50 m/s. No limitation in measuring gas flow to the

required 250 m/s was encountered beyond what was assumed to be Mach number

effects.

10. ACKNOWLEDGMENTS

This work was supported by National Aeronautics and Space Administration,

Marshall Space Flight Center through Government Order #H-63458B. The author

is indebted to the Public Service Company of Colorado and to the City of

Boulder Water Utility for providing the high pressure water so necessary for

these tests. The author would also like to thank Douglas M. Ginley v^o

assisted with parts of this work.

84
1 1 . REFERENCES

[1] Bean, H.S. Editor, Fluid Meters, Their Theory and Application, 6th

Edition, The American Society of Mechanical Engineers, New York, (1971).

[2] White, D.F., Redely, A.E., and McMurtrie, C.L., "The Vortex Shedding

Flowmeter", Flow, Its Measurement and Control in Science and Industry,

Instrument Society of America, 1 (2) 967-97^, (197^).

[3] Lynworth, L.C., Physical Acoustics, Vol. XIV, Mason, W.P., and

Thurston, R.M., editors; Academic Press, New York (1979).

[4] Inkley, F.A., Walden, D.C., and Scott, D.J., "Flow Characteristics of

Vortex Shedding Flowmeters," Meas . and Control (GB) J_3, 156 (1980).

[5] Wiktorowicz, W.E., "Flow Measurement by Vortex Shedding Meters,"

Proceedings, 57th School of Hydrocarbon Measurement, Norman, OK, 1982,

618. Available from K.E. Starling, 202 West Boyd, Norman, OK 73019.

[6] Prandtl, L., Essentials of Fluid Dynamics, Hafner, New York 1952; page

183 ff.

[7] Cousins, T., Foster, S.A., and Johnson, P. A., "A Linear and Accurate

Flowmeter using Vortex Shedding," Symposium of Power Fluidics for Process

Control, 45-56. Guildford, England: University of Surrey, 1973.

[8] Corpron, G.P., Mattar, W.M., Richardson, D.A., and Sgourakes, G.E.,

"Fluctuating Pressure Profile and Sensor design for a Vortex Flowmeter,"

ASME Annual Winter Meeting (San Francisco, CA Dec 15-18, 1978). American

Society of Mechanical Engineers, New York, 1979.

[9] Takamoto, M., and Komiya, K., "A Vortex Ring Shedding Flowmeter," Acta

Imeko, Akadimiai Kiad6, Budapest, Hungry 1982.

85
[10] Kalkhof, H-G., "Influence of the bluff body shape on the measurement

characteristics of vortex flowmeters," International Conference on the

metering of Petroleum and its Products, London Press Centre, London ED4,

1985.

[11] Roshko, A., "Experiments on flow past a circular cylinder at very high

reynolds number," Journal of Fluid Mechanics W_, 345-356 (1961).

[12] Ericsson, L.E., "Karman Vortex Shedding and the Effect of Body Motion,"

AIAA Journal j_8, 935-944 (1980).

[13] Flora, C. and Matsuura, T.K., "Vortex Flowmetering," Meas . and Control

(GB) j_5, 165-170 (1982) .

[14] Colorado Engineering Experiment Station Inc, 54043 County Road 37, Nunn,

Colorado 80648. Their choked nozzle flow standards were used for the

flow velocity calibration.

[15] Padmanabhan, M. and Janik, C.R., "Swirling Flow and Its Effect on Wall

Pressure Drop Within Pipes", Vortex Flows, ASME Winter Annual Meeting

(Chicago, IL, Nov. 16-20, 1980). American Society of Mechanical

Engineers, New York (1981).

[16] Miller, R.W., Flow Measurement Engineering Handbook, McGraw-Hill, New

York (1983).

[17] Mair, W.A., and Beavan, J. A., Modern Developments in Fluid Mechanics,

High Speed Flow, Vol. II, L. Howarth, Editor, Oxford University Press,

London (1953).

This is not intended to be a product endorsement.

86
NBS-IUA (REV. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1, PUBLICATION OR

REPORT NO.

NBS/TN-1302

2. Performing Organ. Report No, 3. Publication Date

October 1986

4. TITLE AND SUBTITLE

VORTEX SHEDDING FLOW METER PERFORMANCE AT HIGH FLOW VELOCITIES

5. AUTHOR(S)

J. D. Siegwarth

6. PERFORMING ORGANIZATION (/fjo/nt or other than N6S. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. H-63458B

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fStreet. City. State, ZIP)

NASA Marshall Space Flight Center

Huntsville

Alabama 35812

10. SUPPLEMENTARY NOTES

Q^ Document describes a computer program; SF-I8S, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

In some of the ducts of the space shuttle main engines (SSME), the maximum

liquid oxygen flow velocities approach 10 times those at which liquid flow

measurements are normally made. The hydrogen gas flow velocities in other ducts

exceed the maximum for gas flow measurement by more than a factor of 3. The results

presented here show from water flow tests that vortex shedding flow meters of the

appropriate design can measure water flow to velocities in excess of 55 m/s, which

is a Reynolds number of about 2 x 10^. Air flow tests have shown that the same

meter can measure flow to a Reynolds number of at least 22 x 10®. Vortex shedding

meters were installed in two of the SSME ducts and tested with water flow. Narrow

spectrum lines were obtained and the meter output frequencies were proportional to

flow to ±0.5^ or better over the test range with no flow conditioning, even though

the ducts had multiple bends preceding the meter location. Meters with the shedding

elements only partially spanning the pipe and some meters with ring shaped shedding

elements were also tested.

12. KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

air flow; cryogenic; flowmeter; hydrogen; liquid oxygen; vortex shedding; water flow.

13. AVAILABILITY

[^ Unlimited

I I For Official Distribution. Do Not Release to NTIS

fX] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Q2| Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

94

15. Price

ft- U.S^ GOVERNMENT PRINTING OFFICE:1986— 773-490/65003 USCOMM-DC 6043-P80



NBSTechnical Publications

Peri&dical

Joumai of Research—The Journal of Research of the National Bureau of Standards reports NBS research and development in those disciplines of the physical and engineering sciences in which the Bureau is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad

range of subjects, with major emphasis on measurement methodology and the basic technology underlying

standardization. Also included from time to time are survey articles on topics closely related to the Bureau's

technical and scientific programs. Issued six times a year.

Nonpenodicals

Monographs—Major contributions to the technical literature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering <ind industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists,

engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties

of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide pro- gram coordinated by NBS under the authority of the National Standard Data Act (Public Law 90-396).

NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published quarterly for NBS by

the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints,

and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and perfor- mance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject

area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized re- quirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private

sector standardizing organizations.

Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace.

Order the above NBS publications from: Superintendent of Documents, Government Printing Office,

Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR's—from the National Technical Information Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FTPS PUBV—PubUcations in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the official source of

information in the Federal Government regarding standards issued by NBS pursuant to the Federal Prop)eny

and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 1 1717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS

for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161, in paper copy or microfiche form.
U.S. Department of Commerce

National Bureau of Standards

Gaithersburg, MD 20899

Official Business

Penalty for Private Use $300