NASA/TM--2002-211985 AIAA-2003-1089

Setting up a Rayleigh

Measuring System in

Testing Facility

Scattering Based Flow

a Large Nozzle

Jayanta Panda

Ohio Aerospace Institute, Brook Park, Ohio

Carlos R. Gomez

Glenn Research Center, Cleveland, Ohio

November 2002

https://ntrs.nasa.gov/search.jsp?R=20030005479 2018-05-15T15:33:40+00:00Z
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NASA/TM--2002-211985 AIAA-2003-1089

Setting up a Rayleigh

Measuring System in

Testing Facility

Scattering Based Flow

a Large Nozzle

Jayanta Panda

Ohio Aerospace Institute, Brook Park, Ohio

Carlos R. Gomez

Glenn Research Center, Cleveland, Ohio

Prepared for the

41st Aerospace Sciences Meeting and Exhibit

sponsored by the American Institute of Aeronautics and Astronautics

Reno, Nevada, January 6-9, 2003

National Aeronautics and

Space Administration

Glenn Research Center

November 2002
Acknowledgments

The authors acknowledge useful advice from Dr. Richard G. Seasholtz, NASA Glenn Research Center, and help in

Labview programming from Kristie A. Elam, Akima Corporation.

The Aerospace Propulsion and Power Program at

NASA Glenn Research Center sponsored this work.

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Available from

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Available electronically at http://gltrs.grc.nasa.gov
Setting up a Rayleigh Scattering Based Flow Measuring System

in a Large Nozzle Testing Facility

Jayanta Panda*

Ohio Aerospace Institute

Brook Park, Ohio 44142

Carlos R. Gomez

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

A molecular Rayleigh scattering based air density

measurement system has been built in a large

nozzle testing facility at NASA Glenn Research

Center. The technique depends on the light

scattering by gas molecules present in air; no

artificial seeding is required. Light from a single

mode, continuous wave laser was transmitted to

the nozzle facility by optical fiber, and light

scattered by gas molecules, at various points along

the laser beam, is collected and measured by

photon-counting electronics. By placing the laser

beam and collection optics on synchronized

traversing units, the point measurement technique

is made effective for surveying density variation

over a cross-section of the nozzle plume. Various

difficulties associated with dust particles, stray

light, high noise level and vibration are discussed.

Finally a limited amount of data from an

underexpanded jet are presented and compared

with expected variations to validate the technique.

I. INTRODUCTION

Typically, large testing facilities in various

industrial and government facilities, involving high

speed flow, have limited options for

instrumentations to measure flow parameters such

as velocity, temperature, and density. Flow

information is usually inferred from schlieren

visualization. Despite the desire to use

Computational Fluid Dynamics (CFD) simulations,

validation of the codes is again hampered due to a

lack of quantitative experimental data. The present

work is a part of an ongoing eftbrt to develop the

* Senior member, AIAA

Rayleigh scattering based technique to provide

benchmark data. In principle, a single measurement

of Rayleigh spectrum provides a measure of

density, temperature, and one component of

velocity by non-intrusive means.

The lack of aerodynamic data from full scale or

large scale model testing is primarily due to the

problems in using the traditional experimental tools

which either are too intrusive or uses seed particles.

Mounting intrusive probes, such as a rake of pitottubes or thermocouples in high-speed, high

temperature flows is not always easy due to

structural and vibration issues. Frequently the probe

and the mount can cause undesirable alteration of

the flow. Hot-wire anemometry, a universal

laboratory tool, is hardly used for similar reasons.

Recent advancement of non-intrusive laser based

techniques is promising; however, commercially

available Laser-Doppler Velocimetry (LDV) and

Particle Image Velocimetry (PIV) require the use of

seed particles which bring a new set of problems.

Seeding a large volume of flow can be challenging,

seed particles contaminate facility and coat models

and windows, and often time the particles are

abrasive. In addition, there are measurement

uncertainties from various biasing errors in

turbulent flows, problems associated with seed

particles passing through shock waves, and beam

steering effects from sharp density gradients. The

Rayleigh scattering technique, on the other hand,

depends on the light scattering from air molecules.

Since, no seed particles are used and only a single

beam is necessary, many problems associated with

NAS A/TM--2002-211985 1
LDV and PIV can be overcome. Moreover,

information is obtained directly from the molecular

distributions; therefore, the Rayleigh scattering

technique is a more fundamental way of measuring

flow properties. 1 Implementation of this technique,

however, requires some special attention to issues

such as cleanliness of air, suppression of

background light etc., which are discussed in this

paper.

In the past, a number of Rayleigh scattering based

optical flow diagnostic techniques have been

developed. Since the Rayleigh scattering crosssection is different for different gas molecules,

mixing between two different species can be

measured from a variation of scattering intensities]

For a fixed composition gas mixture, such as air, the

Rayleigh scattering technique has been used to

measure velocity, temperature, and density over an

area 3'4 or at a point. 5 8 The former uses a tunable

laser and molecular absorption filters, such as the

hyperfine absorption lines of Iodine vapors, and has

the obvious advantage of data collection from a

large number of points. The latter uses continuous

wave laser and high-resolution optical spectrum

analyzer, such as a Fabry-Perot interferometer, and

has the advantage of accuracy and ability to

measure unsteady turbulent statistics of density and

velocity fluctuations. 7'8 The present work follows

the second methodology, which perhaps is better

suited for larger facility that may require light

transmission through optical fibers.

Rayleigh scattering Principles: When a laser

beam is allowed to pass through a gas, the

molecules present in the gas cause inelastic and

elastic light scattering. The inelastic part is called

Raman scattering and the elastic part as Rayleigh

scattering. The Raman scattering cross-section is

substantially weaker than that of Rayleigh

scattering; typically for Nitrogen at room

temperature vibrational and rotational Raman

scattering contribute 0.1 and 1 percent of the total

scattered light I respectively. Therefore, the elastic

Rayleigh scattering process describes most of the

scattered light. For gas density measurement,

variation of the total light intensity with the

molecular number density is of interest. Since this

variation is identical for both Rayleigh and Raman

scattering process, a separation between the two is

unnecessary. The current setup was used to

measure air density only. However, the following

surmises principles to measure all three quantities:

density, temperature, and a component of

velocity.

A simplistic description of the measurement

process, using optical spectrum analysis of

Rayleigh scattered light is schematically shown in

Fig. l(a). Since the Doppler shift frequency is of

the order of a few Gigahertz, a narrow line width

(of the order of 10MHz) incident laser beam is

necessary to resolve the Rayleigh spectrum. In the

case of a moving gas media, the bulk motion is

superimposed on the random velocity of the

individual molecules; therefore shift between the

peaks of the incident laser line and the Rayleigh

spectrum provides a measure of the bulk velocity.

The Full Width at Half Maxima (FWHM)

depends on the spread of molecular motion and,

therefore, is a measure of gas temperature.

Finally, the total light under the Rayleigh

spectrum is proportional to the molecular number

density and provides a measure of gas density.

Figure l(b) presents a scattering diagram, where

K i is the incident wave vector, Ks is the scattered

wave vector pointing towards the collection optics

and, K = Ks - Ki, is the scattering vector. For IKsl

IKil, the magnitude of the scattering vector

becomes K = 2 Ki sin(0s/2), and the Doppler shift

from the bulk velocity U of the flow is

2Uco *

f,__ K.U _ (_)

2_ _i

where, qb is the angle between the scattering

vector K and the velocity vector U, and )b i is the

wavelength of the incident light. The measured

component of velocity is Vr = U COM). The same

Doppler shift principle applies to the individual

molecules as well. If the gas molecules are

assumed to have a Maxwellian velocity

distribution and if Brillouin scattering is assumed

to be negligible then the bandwidth (Full Width at

Half Maxima) of Rayleigh spectrum becomes

NAS A/TM--2002-211985 2
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiLase_iiiiiiii

iiiiiiiiiiiiii i i iiiiiiiiiiiii igii tii)i i i i i i iiiiiiiiiiiiiiiiiiiii

Figure l. (a) Schematic to explain velocity, temperature and density measurement

from Rayleigh Spectrum; (b) Scattering diagram.

Af= 0.265K(_--_11 / 2

(2)

where, kB is the Boltzmann's constant, m is

molecular mass and T is gas temperature. Clearly,

for a fixed optical setup (K fixed) and a given gas

mixture (m fixed) the bandwidth of Rayleigh

spectrum is proportional to the square root of

temperature.

The density of the gas/gas-mixture is proportional

to the area under the spectrum. Therefore, to

measure density alone no optical spectrum

analysis is required; a measure of total scatter

light is sufficient. The intensity of total scattered

light Ps collected from a probe volume, Vsc into a

solid angle, d.Q, can be written as:

do 2 k'

Ps=nlOVsc_-sin zdf2= n. (3)

Here n is the molecular number density, I0 is the

incident light intensity, do/d.Q is the differential

Rayleigh scattering cross-section of the gas (or gas

mixture) under consideration, Z is the angle

between the incident electric vector and the

direction of light collection, and k' is a constant. The

Rayleigh scattering cross-section depends on the

light wavelength and the effective molecular

diameter. This is constant for a fixed wavelength

laser and a fixed gas mixture (air for this work). For

a fixed optical setup, the scattered laser power is

directly proportional to the molecular number

density, which in turn is directly related to the bulk

density, p. Therefore,

Ps =k"p (4)

where k" is a constant. Now the scattered light

intensity was measured using a photomultiplier tube

and a photon counting process was used. The

number of photons N collected during a fixed time

interval At can be written as:

N- cPsAt -kp At (5)

hv

where, h is the Planck constant, v is the frequency

of the laser light and 8 is the overall collection

efficiency (a product of the light transmission

efficiency and the quantum efficiency of the

photomultiplier tube). Equation 5 shows that the

photon count over a fixed time interval is directly

proportional to the gas density at the probe

volume. The proportionality constant k has to be

determined through a calibration process.

Typically, the overall collection efficiency was

about 5 percent.

NAS A/TM--2002-211985 3
II. EXPERIMENTAL SET UP

The measurement system was setup in an

advanced nozzle and engine component test

facility 9 in the Engine Research Building of the

NASA Glenn Research Center. A schematic of the

facility is shown in Fig. 2. The nozzle itself is

enclosed in a large stainless steel tank of 7.5 feet

diameter and 23 feet length. The tank is split into

a fixed and a movable part; the latter is retracted

downstream to allow access to the model. When

closed, an inflatable rubber seal prevents leakage

through the joint. Static pressure below ambient

value is maintained in the tank to simulate various

high altitude engine operations. Two different

compressed air lines supply the model, and the

tank is connected to a vacuum (altitude exhaust)

system. All of these air lines come from a

centrally located supply that provides for all the

facilities in the center. The primary compressed

air is a 40psi (276 kPa) supply that can deliver up

to 40 lb/s (18 kg/s) of continuous unheated flow

or 30 lb/s (13.6 kg/s) of heated (370°F max) flow.

The secondary compressed air is a 450 psi

(3.1 MPa) supply that can deliver unheated air at a

maximum rate of 8 lb/s (3.6 kg/s).

The optical access to the facility is through a pair

of 23 inch (0.584 m) diameter schlieren windows.

The nozzle was installed such that upon closing

the tank, the upstream edges of schlieren windows

lined up with the nozzle lip. There is a flow

collector 21 inch (0.533 In) downstream of the

nozzle lip. Therefore, a limited extent of the

plume, bounded by the diameter of the schlieren

windows and the location of flow collector is

measurable in this facility.

The present paper reports a limited amount of data

collected from a convergent, 20 in] exit area

(5.046 inch or 0.128m diameter), circular

geometry nozzle that was supplied by the primary

40 psi (276 kPa) compressed air supply. The

nozzle was operated in trader-expanded condition

at Nozzle Pressure Ratio = 10 (P0= 18.2 psi or

125.6 kPa, To = 540R or 300K).

Figure 2. Sketch of the advanced nozzle and engine component test facility.

NASA/TM--2002-211985 4
Figures 3 and 4 show a sketch and a photograph of

the optical arrangement respectively. The

photograph was taken with the movable part of the

tank retracted downstream. The schlieren windows

are positioned farther left and are not visible in the

photograph. The sketch, on the other hand, shows

the final setup with tank closed. Green laser light at

532 nm wavelength from a solid state, frequency

doubled, single mode, Nd:VO4 Laser was

transmitted inside the enclosing tank via a single

mode, polarization maintaining optical fiber.

Although the laser is capable of producing 5 watts

of power, the capacity of the 4micron core diameter,

pure silica, optical fiber limited the available light in

the tank to 400 milliWatts only. The transmitted

part of the beam was collimated and deflected

downward to be at the center plane of the nozzle

plume. The beam ultimately dissipated in a long

beam dump that was laid parallel to the flow

direction. The transmission optics in the tank also

included a laser power meter, which monitored the

transmitted laser power and was helpful in coupling

the laser beam to the optical fiber. The polarization

plane of the laser beam was adjusted for the peak

scattering orientation to line up towards the

collection optics.

Light scattered by air molecules from the laser

beam was collected through one of the schlieren

windows by a 150 mm diameter f/10 achromat,

depicted as L1 in Fig. 3, placed outside the tank.

Another 150 mm diameter f/3 achromat, depicted as

L2 in Fig. 3, focused the collected light on a 0.9 mm

high and 0.4 mm wide slit. Light passing through

the slit was focused on the cathode surface of a

photomultiplier tube (PMT). The height of the slit

and the imaging ratio of the collection optics fixed

the probe volume length to 3 mm. The transmission

beam diameter was about 1 mm; the slit width was

sufficient to allow light scattered from entire beam

diameter to reach PMT. The collection assembly

was mounted on an X-Y traverse while the

transmission optics inside the tank was mounted on

a single X-traverse. The combination allowed

survey of the jet plume over a longitudinal plane.

The X-traversing units were synchronized to move

along axial direction, while the Y-traversing trait

allowed light to be collected from various vertical

positions on the beam.

The success of a Rayleigh scattering system is

dependant on close attention to some additional

details such as, removal of dust particles from air

flow, attenuation of stray scattered light and

separation of sensitive optical components from

vibration and noise sources. The dry compressed air

from the central facility was passed through

additional filters, situated inside the test cell, before

arriving at the model. An examination of residues in

these existing filter housings showed that the 40 psi

air was contaminated by some amount of desiccant

particles and the 450 psi line by fine rust from an

old header. The supply lines from the filter hosing

to the model were made of stainless steel, the

interior of which did not rust, but the 450 psi line

had a thin coating from rust particles that escaped

the existing coarse filters. An acceptable solution

was obtained by using fine filters that removed

99.8 percent of all particles above 0.3 micron size in

both the airlines. Large surface area of the filters

ensured small pressure drop across the filter

housing. The existing rust particles from 450 psi

line were purged by allowing the maximum air flow

(with the fine filer in place) for a couple of hours. A

time signature of PMT current provides an easy

check on the cleanliness. Since particle (Mie)

scattering is a few orders of magnitude stronger

than the Rayleigh scattered light, passage of most

dust particles lead to a sharp rise in PMT current.

Nevertheless, a few particles--in the present

experiment about 100/sec.--are deemed tolerable

for time averaged density measurement. In an open

jet facility, one needs to provide clean dust free air

for the entrained flow as well. 7'8The large enclosure

tank, in spite of a source of many other difficulties,

eliminated this problem, as the trapped air inside the

tank was quickly replaced by clean supply air

within a couple of minutes of operation.

To reduce background light level, the beam dump

was designed to minimize back scattering and

various baffles were placed around optical

components inside the tank. The second schlieren

window was covered by black cloth to provide a

dark background. All windows in the test cell were

covered and all lights inside the test cell were turned

off. The facility itself was operated remotely from

an adjoining control room. All other aspects of the

Rayleigh scattering experiment were also controlled

from this room.

NASA/TM--2002-211985 5
Single mode optical fiber

- _ _::_ _:vo_

couplerFiber-optic Laser Tan

/ _ ._J \

__/ Monting beams _ _ Schlieren window

to photon

L1 L2 slit _ounter

Nozzl

Collection optics _/"

-- on X-Y traverse ÷

Figure 3. Schematic of the optical setup.

Figure 4. Photograph of the optical arrangement. The enclosing tank was retracted downstream.

NASA/TM--2002-211985 6
The fiber-based light transmission system was

mostly successful to separate the laser source from

the high level of facility vibration. However, the

mechanical motmting and positioning units for

coupling laser light to the optical fiber was found to

be sensitive to facility vibration. The core diameter

of the single mode fiber was 4 micro-meter and

small vibration easily affected coupling efficiency,

which resulted into some unsteadiness in the laser

light transmitted inside the tank. The Rayleigh

scattering technique can be used to measure density

variations associated with turbulent fluctuations in

the plume; 7'8 however, since the incident light itself

fluctuated, such measurements were impossible in

the present setup. The time-averaged measurements

were not affected as the power meter provided a

measure of average transmitted power. In the

present setup the fiber coupler was placed in the

same test cell with the facility, and therefore, was

subjected to a relatively high level of vibration and

noise. In future, the laser and the coupling

arrangement will be placed in the adjoining control

room to avoid this problem.

Data acquisition and processing: The low level of

the scattered light called for a photoelectron

counting system. A counter that provided counts

over a series of 16384 contiguous bins of

specified time duration was used. The passage of

stray particles was identified and the specific time

bins were rejected through software based postprocessing that rejected data points beyond 5

times the standard deviation. Note that such a

software-based technique cannot remove excess

counts from small particles moving at a faster

speed or weaker signatures from particles passing

through the edges of the beam. The photoelectron

counter and all traversing units were controlled

remotely. So was the monitoring for facility

pressure and temperature probes, mass flow

devices and transmitted laser power.

Alignment of the collection optics, so that the

image of the beam is centered at the slit at all

axial and radial locations, became an important

issue (fig. 3). The transmission optics inside the

tank and the collection optics outside were placed

on separate traverses. Various factors, such as

thermal contractions from progressive cooling of

the tank, small irregularities in the schlieren

window and small error in alignment caused the

image of the probe volume from various parts of

the laser beam to drift outside the slit aperture. To

mitigate this problem, the slit was centered at

every measurement point by surveying the change

in photoelectron count while the collection optics

is moved axially by very small increments. The

axial position that provided peak count

corresponded to the best alignment. Such surveys

were performed before acquiring data from any

measurement point.

IlL RESULTS

Time-averaged density data were measured via

photon counting over a 5.4 sec interval. A

calibration process is necessary to determine the

proportionality constant between the rate of

photon count N, and the air density p; as well as

to determine the residual stray light collected

through the optics. Plumes at various known

density conditions were easily obtained by

changing both the supply pressure P0 and tank

pressure Pt. The air density at the plume core can

be determined from isentropic relation till a

choked condition, NPR _<1.89, is reached:

1

P P0 (P0/-T =5T0 j (6)

where, T0 is the total temperature of supplied

compressed air, R is the universal gas constant,

and T is the ratio of specific heats. The photon

arrival rate was counted at different operating

conditions and a straight line,

N = (a P + b) At (7)

was fitted through the data (fig. 5) using the leastsquares method. The slope of the line provided the

proportionality constant as shown in equation 5,

and the intercept provided a measure of the stray

light. It should be pointed out that the density

variations, encountered in the underexpanded jet

plumes, occur over a wider range than the range

used for calibration. However, the calibration is

expected to remain valid over the entire range due

to the fundamental linear relationship between the

molecular number density and the intensity of

scattered light.

NASA/TM--2002-211985 7
lx10 6 - . . , .... . . . , - . . , . + ,

8x_O 5

m 6xi0 5

0_4×10 5

2X10 5

0

. . . s . . . • . . . i . . . K . . .

0.0 0+2 0+4 0+6 0.8 1+0

density (kg/m**3)

Figure 5. Air density versus photoelectron

count calibration.

The fundamental error source in the time-averaged

measurements arises from the electronic shot noise

that manifests as the statistical photon count noise.

The shot noise is proportional to the variance of the

number of photons (N) detected over a fixed time

interval in repeated measurements. Since the

detection of photons obeys Poisson's statistics,

variance of the photon count is equal to the average

number of counts, i.e., r_N = N. As a result the

relative uncertainty in the measurement of N is

given by

ol/2

N _ N-l/2.

N

(8)

For the present experiment the count rate was

high; over a 5.4 second interval the number

counted was between 1 to 5 million. Therefore,

the uncertainty from the shot noise was below

0.1 percent. Since, the contribution from the

fundamental noise source was very low, that from

a host of secondary sources became prominent.

Occasional particles were unavoidable and their

passage led to an increase in the photon count. As

mentioned earlier, vibration from the facility

caused unsteadiness in the transmitted laser

power. Finally, alignment between the slit in the

collection optics and the laser beam inside the

tank brought additional random uncertainty in

density measurement. These secondary noise

sources are difficult to quantify. It is expected that

some of the sources lead to bias error and the

others to random error (precision error). The

calibration of photon arrival rate against known

density values is expected to account for some of

the bias error. The random part of the uncertainty

was estimated to be about +5 percent of the

reported value. Usually, a calibration curve was

obtained at the beginning or at the end of a day,

and was used for all data acquired in that day.

Figure 6(a) shows a density survey along the

centerline of an underexpanded (NPR = 10, P0 =

18.2 psi, To = 540 R) plume from a convergent

nozzle. Air density progressively fell as the flow

expanded till a Mach disk is formed at x/D = 2.1.

Subsequently, there occurs a sudden jump, as

expected across a normal shock. The flow field

immediately downstream of the choked nozzle,

and bounded downstream by the Mach disk and

radially by an incident shock originating from the

nozzle lip, I° is driven by isentropic expansion.

The variations of flow Mach number and

thermodynamic parameters can be easily

predicted numerically through the Method of

Characteristics. Owen and Thomhil111 presented

one such calculation. For the present work a

slightly different scheme outlined by Shapiro 12

was used. An excellent agreement between the

measured density variation and the numerically

calculated values goes towards the validation of

density measurement technique. Figure 6(b)

shows a radial profile obtained close to the nozzle

exit. The cold plume had a higher density than the

ambient. The shear layer and incident shock

around the plume periphery created the sharp

density gradient leading to the jet core.

IV. CONCLUDING COMMENTS

One of the strengths of Rayleigh scattering based

technique is the ability to simultaneously obtain

intbrmation about flow density, temperature, and a

component of velocity from a single measurement.

The last two require spectral analysis of the collected

light while the first does not. Therefore density

measurement serves as a first step towards the

realization of the technique's full potential. The

basic requirements, such as the cleanliness of the

airflow, suppression of background light and

effective vibration isolation, have been reasonably

fulfilled in the current setup. It is hoped that in future

entries the remaining problem with vibration will be

properly addressed and the optical setup will be

expanded to measure temperature and velocity.

NASA/TM--2002-211985 8
(a)

+

o.o

0 I 2 3

axial distance from nozzle/diameter

4

_++

+

÷ +

÷ + +

.... | .... i .... i ....

- 1,0 -0.5 0.0 0.5 .0

Radial distance from centeriine/diameter

Figure 6. Density data from the plume of a cold, NPR 10, jet from a convergent nozzle. (a) Centerline

variation: + experimental data, solid line-expected variation; (b) Radial profile at x/D = 0.3.

References

1. Miles, R.B., Lempert, W.R., and Forkey, J.N.,

2001, Laser Rayleigh scattering. Meas. Sci.

Technol. 12, R33-R51.

2. Pitts, W.M., and Kashiwagi, T., 1984, The

application of laser-induced Rayleigh scattering

to the study of turbulence mixing. J. Fluid

Mech., 141 391-429.

3. Forkey, J.N., Lempert, W.R., and Miles, R.B.,

1998, Accuracy limits for planer

measurements of flow field velocity,

temperature and pressure using filtered

Rayleigh scattering. Experiments in Fluids,

24, 151-162.

4. Elliott, G.S. and Samimy, M., 1996, Rayleigh

scattering technique for simultaneous

measurements of velocity and thermodynamic

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5. Seasholtz, R.G., Zupanc, F.J., and Schneider,

S.J., 1992, Spectrally resolved Rayleigh

scattering diagnostic for hydrogen-oxygen

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S(5), 935-942.

6. Panda, J., and Seasholtz, R.G. 1999 Velocity

and Temperature Measurement in Supersonic

Free Jets Using Spectrally Resolved Rayleigh

Scattering. AIAA paper 99-0296.

7. Panda, J. and Seasholtz, R.G., 2002,

Experimental investigation of density

fluctuations in high-speed jets and correlation

with generated noise, Journal of Fluid

Mechanics, vol. 450, pp. 97-130.

8. Seasholtz, R.G., Panda, J., and Elam, K.A.,

2002, Rayleigh scattering diagnostic for

measurement of velocity and density

fluctuation spectra, AIAA paper 2002-0827.

9. Beltran, L.R., Del Roso, R.L., and Del

Rosario, R., 1992, Advanced Nozzle and

Engine Component Test facility, NASA TM

103684.

10. Panda, J., and Seasholtz, R.G., 1999, Shock

structure and shock-vortex interaction in

screeching jets measured using Rayleigh

scattering, Physics of Fluids, vol. 11, no. 12,

3761-3777.

11. Owen, P.L., and Thornhill, C.K., 1952, The

flow in an axially-symmetric supersonic jet

from a nearly-sonic orifice into a vacuum,

Aeronautical Research Council Report &

Memoranda no. 2616.

12. Shapiro, A.H., 1953, The Dynamics and

Thermodynamics of Compressible Fluid Flow,

Vol. II, John Wiley & Sons, pp. 676.

NASA/TM--2002-211985 9
Form Approved REPORT DOCUMENTATION PAGE

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintainingthe data needed, and completing and reviewingthe collection of information. Send comments regarding this burden estimate or any other aspect of this

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

November 2002 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Setting up a Rayleigh Scattering Based Flow Measuring System in a Large

Nozzle Testing Facility

6. AUTHOR(S)

Jayanta Panda and Carlos R. Gomez

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

WU-708-90-43-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-13655

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--2002-211985

AIAA-2003-1089

11. SUPPLEMENTARY NOTES

Prepared for the 41 stAerospace Sciences Meeting and Exhibit sponsored by the American Institute of Aeronautics and

Astronautics, Reno, Nevada, January 6-9, 2003. Jayanta Panda, Ohio Aerospace Institute, 22800 Cedar Point Road,

Brook Park, Ohio 44142; Carlos R. Gomez, NASA Glenn Research Center. Responsible person, Jayanta Panda,

organization code 5860, 216-433-8891.

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified -Unlimited

Subject Category: 45 Distribution: Nonstandard

Available electronically at http://gltrs.arcmasa.gov

This publication is available from the NASA Center for AeroSpace Information, 301-621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

A molecular Rayleigh scattering based air density measurement system has been built in a large nozzle testing facility at

NASA Glenn Research Center. The technique depends on the light scattering by gas molecules present in air; no artificial

seeding is required. Light from a single mode, continuous wave laser was transmitted to the nozzle facility by optical

fiber, and light scattered by gas molecules, at various points along the laser beam, is collected and measured by

photon-counting electronics. By placing the laser beam and collection optics on synchronized traversing units, the point

measurement technique is made effective for surveying density variation over a cross-section of the nozzle plume. Various

difficulties associated with dust particles, stray light, high noise level and vibration are discussed. Finally, a limited

amount of data from an underexpanded jet are presented and compared with expected variations to validate the technique.

14. SUBJECT TERMS

Rayleigh scattering

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

NSN 7540-01-280-5500

15. NUMBER OF PAGES

15

16. PRICE CODE

18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

OF THIS PAGE OF ABSTRACT

Unclassified Unclassified

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102