t? H B? fc, S \i

(NASA-CE-176386) PERFORMANC E TESTS FOR THE N86-27292

NAS A AME S RESEARC H CEN1ER 20 cm X 40 cm

OSCIL1ATING F10K WIN D TUNNE L Progress

Eeport, 1 Jun. - 31 Dec. 1984 (Iowa State Unclas

Univ. of Science and Technology) 46 p G3/09 43311

ENGINEERING

RESEARCH

INSTITUTE

IOWA STATE

UNIVERSITY

AMES, IOWA

Progress Report

Performance Tests for the NASA Ames

Research Center 20 cm x 40 cm

Oscillating Flow Wind Tunnel

William J. Cook, Professor

Department of Mechanical Engineering

and

Tim A. Giddings, Graduate Student

Department of Mechanical Engineering

December 31, 1984

n <^

a a
ISU-ERI-Ames-85436

Progress Report for the period June 1, 1984 to December 31, 1984

Project 1601

Submitted to the NASA Ames Research Center under

Grant No. NCC2-200 entitled "Study of

Turbulent Boundary Layers in Oscillating Flows"

W. J. Cook, Principal Investigator

J. D. Murphy, Grant Technical Monitor

Progress Report

Performance Tests for the NASA Ames

Research Center 20 cm x 40 cm

Oscillating Flow Wind Tunnel

William J. Cook, Professor

Department of Mechanical Engineering

and

Tim A. Giddings, Graduate Student

Department of Mechanical Engineering

December 31, 1984

engineering

research institute

iowa state university COLLEGE OF ENGINEERING , AMES, IOWA 50011
ii

TABLE OF CONTENTS

Page

NOMENCLATURE iii

SUMMARY 1

INTRODUCTION .' 1

FACILITY DESCRIPTION 2

STEADY FLOW EXPERIMENTS 3

Steady Mainstream Flows 4

Steady Boundary Layer Flows 5

Comments on Steady Flow Experiments 8

OSCILLATING FLOW EXPERIMENTS 9

Mainstream Oscillating Flows 9

Oscillating Boundary Layer Flows 12

Comments on O.scillating Flow Experiments 14

CONCLUDING REMARKS 15

REFERENCES 16

TABLES 17

FIGURES 19
ill

NOMENCLATURE

C

Cf

f

H

M

o

Re

U

sonic velocity

centerline

friction coefficient,

frequency, Hz

boundary layer shape

factor, 6*/9

test section length

mean Mach number, U /a

' o

Reynolds number based on

momentum thickness

Re Reynolds number based on x

X

S Mach number variation,

equations (5) and (5a)

t time

u x component of boundary

layer velocity, ensemble

average

u' fluctuating component of

velocity

friction velocity, [T /p]

W

mainstream velocity,

ensemble average

centerline velocity,

Figure 3

axial distance measured

from test section entrance

distance perpendicular to

test section wall

B

6

6*

9

w

phase angle, equation (6)

steady flow velocity boundary

layer thickness

displacement thickness

momentum thickness, phase

angle, equation (5) and (5b)

coefficient of viscosity

y/p

density

wall shear stress

phase angle, equation (7)

angular frequency, radians/sec

reduced frequency, wx/U

Subscripts:

mean velocity based on ensemble

average

amplitude of velocity variation

based on ensemble averaged

values
Performance Tests for the NASA Ames Research Center

20 cm x 40 cm Oscillating Flow Wind Tunnel

W. J. Cook1" and Tim A. Giddings*

Iowa State University, Ames, Iowa

SUMMARY

This report describes and presents an evaluation of initial tests

conducted to assess the performance of the NASA Ames 20 cm x 40 cm oscillating flow wind tunnel. The features of the tunnel are described and two

aspects of tunnel operation are discussed. The first is an assessment of

the steady mainstream and boundary layer flows and the second deals with

oscillating mainstream and boundary layer flows. Experimental results

indicate that in steady flow the test section mainstream velocity is uniform in the flow direction and in cross section. The freestream turbulence

intensity is about 0.2 percent. With minor exceptions the steady turbulent boundary layer generated on the top wall of the test section exhibits

the characteristics of a zero pressure gradient turbulent boundary layer

generated on a flat plate. The tunnel was designed to generate sinusoidal

oscillating mainstream flows. Experiments confirm that the tunnel produces

sinusoidal mainstream velocity variations for the range of frequencies

investigated (up to 15 Hz). The mainstream flows were observed to vary in

amplitude and phase in the direction of flow in the upper range of frequency,

as predicted qualitatively by theory. The oscillating flow boundary layer

case studied indicates that boundary layer flows similar to those observed in

other oscillating flow experiments are generated in the tunnel. The results

of this study demonstrate that the tunnel essentially produces the flows

that it was designed to produce.

INTRODUCTION

The NASA Ames 20 cm x 40 cm oscillating flow wind tunnel is located

in the Aerodynamics Research Branch of the Ames Research Center. Its design

is based on a smaller tunnel which is described in References 1, 2, and 3.

The facility was first operated in July of 1984. This report describes and

presents an evaluation :of initial tests performed in July and August of 1984

to assess the performance of the tunnel. Two aspects of tunnel operation

are covered. The first is an assessment of the steady mainstream and

boundary layer flows produced. The second part reports results for oscillating flow experiments for both mainstream and boundary layer flow.

Professor, Mechanical Engineering and Engineering Research Institute

*

Graduate student, Mechanical Engineering Department
FACILITY DESCRIPTION

The 20 cm x 40 cm oscillating flow tunnel is described in Figure 1 and

Table 1. The facility is vacuum driven by means of a line connected to the

Ames Research Center Unitary Wind Tunnel vacuum system. Room air flows into

the test section through the entrance section which has an area contraction

ratio of 9 to 1. The honeycomb and screens in the entrance section are described in Table 1. The test section is nominally 20 cm high and 40 cm wide,

in cross section and is 2.75 m in length. The walls are 2.54 cm thick Plexiglas. The vertical walls diverge in the direction of flow to produce zero

pressure gradient flow when the flow is steady. Instrument ports are provided on the top and bottom walls at several axial locations along the centerlines over the length of the test section. In addition, sliding wall segments are provided on the top and bottom walls at distances 0.15 m and 1.88

m from the test section entrance for surveys in the transverse (z) direction.

During operation, the nozzle discharge-region pressure is low enough to

maintain sonic flow at the nozzle throat. When the position of the wedge in

the wave generator section is fixed, the test section flow is steady. When

the wave generator is operated at a fixed frequency, the test section mainstream flow velocity U is characterized by a mean velocity and a superposed

oscillating component of the form

U(x,t) = Uo + U1(x)Cos Wt (1)

where U is the mean velocity and U, is the half amplitude of the velocity

variation, and 0) is the angular frequency of the wave generator input shaft.

The mean and oscillating velocity components for the test section flow can

be selected within certain limits by choice of the nozzle throat cross section, the wedge leading-edge included angle, and the wedge stroke. The

throat cross section can be altered by changing the nozzle throat blocks
shown in Figure 1. Two sets of blocks were used in the present tests.

These are designated as nozzle block sets A and B and are described in Table

1. A single wedge with an included leading-edge angle of 20 degrees was used.

Table 2 describes the wave generator configurations used in obtaining the

results reported here. The unit Reynolds numbers for the flows associated

with these configurations are such that natural transition from laminar to

turbulent flow would occur in the test section wall boundary layers. Since

it was desired to study turbulent boundary layers on the facility walls,

boundary layer trip wires 0.63 mm in diameter were positioned on the four

walls at the test section entrance to produce boundary layer transition.

4

The wire diameter was chosen to produce transition at the trip .

A hot wire anemometer system was used as the primary means of obtaining

data. Figure 2 describes the anemometer and the data acquisition system.

The complete system was calibrated with the hot wire outside the tunnel using

a TSI Model 1125 air flow calibrator and standard calibration techniques. All

results reported here are based on measurements made through instrument ports

on the top wall of the tunnel.

STEADY FLOW EXPERIMENTS

Studies of the flows associated with wave generator configurations I and

II in Table 2 were conducted to.examine both the mainstream and boundary layer

flows produced in the tunnel under steady flow conditions. For steady flows,

the data acquisition system, Figure 2, was programmed to take 500 hot wire

voltage readings over a 1.5 second time span. Due to minor temperature

changes, system drift, and hot wire contamination due to dust in the test

air, it was necessary to check the hot wire calibration and make appropriate

adjustments before each run. This was accomplished with the tunnel running

by positioning the hot wire probe to a calibration point in the mainstream
flow and adjusting the system to display the calibration voltage. The average velocity and the RMS turbulence was determined by computer processing

the 500 voltage readings. The uncertainty associated with the velocity

measurements was estimated to be i 1 percent*.

Steady Mainstream Flows

The mainstream flows were studied by means of velocity and static pressure measurements. Due to the divergence of the vertical test section walls

to account for boundary layer displacement effects, the pressure drop over

the length of the test section was essentially zero for the steady flows

associated with wave generator configurations I and II. Correspondingly,

there was no measureable change in the mainstream centerline velocity over

the test section length for either flow. Measured values for the centerline

velocities and the test section static pressures are given in Table 2 as

are the corresponding unit Reynolds numbers.

Surveys of the velocity at x = 1.88 m over one half of the test section

cross section were made for the flows produced by wave generator configuration I in order to examine the uniformity of the flow. The results are presented in Figure 3. Surveys were made at three values of y in the upper half

of the test section as indicated in the figure and were confined to the flow

region outside the boundary layers. The results are presented in terms of

U/U vs z, where U is the average of two separate velocity measurements made

on the axial centerline at x = 1.88 m. The results indicate that the mainstream flow is uniform within 1 2 percent variation from the centerline velocity in the region surveyed. The scatter in the results at a given value of

y is related to the uncertainty of i 1 percent in the velocity measurements.

Uncertainties in this report are given as estimates of ir one standard

deviation.
Steady Boundary Layer Flows

Velocity surveys were made for the boundary layer on the top wall at

several axial locations for wave generator configurations I and II in Table

2 (steady flows). The first results to be discussed are those obtained from

surveys made along the top wall centerline.

Velocity profiles u vs y were obtained using the data acquisition system,

Figure 2, and were processed by means of a boundary layer analysis computer

code provided by Westphal to determine various boundary layer parameters.

Figure 4 shows descriptive boundary layer quantities related to the flows

for both wave generator configurations. Figure 4a displays the variation

with x of the momentum-thickness Reynolds number Refl, the Ludwieg-Tillmann

skin friction coefficient Cf given by

C- = T /PspU2] = 0.246xl(f0-

678H

 Re'0'

268

 (2)

t w o o

and the boundary layer shape factor H = 6*/6. Bars indicating the estimated

experimental uncertainty for Re,, are shown. The uncertainties for C_ and H

are approximately the symbol size. For the most part the results in Figure

4a exhibit the trends expected for a turbulent flat plate boundary layer.

However, the value of Refl at x = 1.66 m, Configuration I, lies above the

curve fitted through the remaining points. A possible explanation of this

is that a test section joint lies 13 cm upstream of the instrument port at

x = 1.66 m and joint mismatch may have been present and produced a local

disturbance in the flow.

Figure 4b displays velocity boundary layer thicknesses 6 for the. flows

related to each wave generator configuration. The symbols indicate values

determined from experimental velocity profiles at 99 percent of the boundary

layer edge velocity. Bars indicating the estimated experimental uncertainty

in 6 are shown. Also shown are curves based on the equation
-= 0.371 Re'0

'

2

 (3)

x x

which predicts the velocity boundary layer thickness for turbulent flows

over a flat plate. The predicted variation fits the experimental results

for configuration I well, yielding the expression

6, cm = 1.888(x, m)0'

8 (3a)

However, the experimental results for configuration II lie somewhat below

the curve given by equation (3). The curve fitted through the points for

configuration II is given by

6, cm = 1.72(x, m)°'8 (3b)

This result is somewhat anomalous since a thicker boundary layer should

be associated with the lower mainstream velocity produced by configuration

II. Possibly boundary layer transition did not occur at the trip wire.

Figures 5a and 5b present experimental velocity profiles in terms of

u/U and y/6 for the steady flows related respectively to wave generator

configurations I and II. Values of 6 used in preparing these and subsequent figures involving 6 were determined by use of equations (3a) and (3b)

respectively. The several profiles in both Figures 5a and 5b exhibit essential agreement. Figure 5c compares the velocity profiles at x = 1.35 m and

x = 2.48 m for the two flows. While the profiles agree very well for the two

positions within either flow, a difference exists between the profiles for

the two flows.

Figures 6a and 6b present boundary layer profile results in terms of u+

vs y for the two flows. The bars indicate the experimental uncertainty for

the results at x = 0.44 m, where the uncertainty is the largest. The uncertainty at x = 2.48 m is approximately the symbol size. The uncertainties

result from uncertainties in the freestream velocity. The results for these

figures were obtained using C values predicted by equation (2). The collec-
tive profiles exhibit good agreement .with the logarithmic law equation at

the lower values of y , with the possible exception of the results at x =

0.44 m, Figure 6b. For this case, the turbulent boundary layer may not have

been sufficiently developed, as indicated by the relatively small value of

Re. (ReQ = 2000, see Figure 4a).

u 0

Figures 7a and 7b show percent turbulence intensity defined as

_ «

Turbulence intensity, percent = 100[u'2] /UQ (4)

for the two flows: u' is the fluctuating component of velocity and UQ is the

local velocity in the boundary layer. The results for turbulence intensity

in these figures were obtained by computer processing of the 500 hot wire

voltage readings taken at each y value using the data acquisition system.

Although some scatter exists, results for the several x locations group

fairly closely in both Figures 7a and 7b. Values of freestream turbulence

intensity as indicated by the computer-acquired data are approximately 0.4

percent for both flows. Turbulence intensities were also measured by means

of a Disa 55D35 true RMS meter operated in conjunction with a Disa 55D26

signal conditioner functioning as a 10 kHz low-pass filter to filter out high

frequency noise present in the hot wire system. This noise introduced an

error in turbulence intensity at very low values of turbulence intensity.

Results obtained using these instruments were in essential agreement with

those obtained from the computer-acquired data except in the region outside

the boundary layer. Values of turbulence intensity measured in the mainstream

with the RMS meter were in the range 0.16 to 0.20 percent.

Figure 7c shows a comparison of turbulence intensity profiles at x =

1.35 m and x = 2.48 m for steady flows produced by the two wave .generator

configurations. A difference in the two profiles for the two configurations

is evident. Also shown for comparison purposes are turbulence intensity pro-
files measured in flat plate turbulent boundary layers at two freestream

7 8 turbulence intensities, 0.02 percent and 0.3 percent ' . The experimental results for configuration I agree well with the curve for 0.3 percent turbulence intensity except at low values of y/6 where the results more closely

agree with the curve for 0.02 percent turbulence intensity.

In addition to the top wall centerline boundary layer surveys discussed

above, surveys were made at 11 cm each side of the top wall centerline at

the x = 1.88 m axial location. Comparisons of some results from these surveys

and the centerline survey at x - 1.88 m are presented in Figure 8. Figures

8a, 8b, and 8c show respectively velocity profiles, u vs y , and turbulence

intensity for the three surveys. In each of the figures the results for the

three positions are essentially in agreement, indicating that a uniform turbulent boundary layer is developed across at least 22 cm of the 40 cm wide top

wall.

Comments On Steady Flow Experiments

With minor exceptions, the experimental results indicate that the test

section flows for steady operation of the tunnel are of good quality. The

mainstream flows exhibit uniform velocity for the length of the test ;section

and have relatively low freestream turbulence intensities, approximately 0.2

percent. Based on the good uniformity of the flow observed at the x = 1.88 m

location, it is expected that the flow is equally uniform at other cross

sections. The various boundary layer quantities described in Figures 4

through 8 indicate that turbulent boundary layers similar to those developed

on flat plates with zero pressure gradient were generated on the tunnel top

wall for each of the flows studied. However, the comparisons in Figures 5c

and 7c show some differences between the boundary layers for configuration I
(Uo =45.7 m/s) and those for configuration II (UQ =26.6 m/s). These differences may be related to the fact that the boundary layer velocity thicknesses

for configuration II flows are less rather than greater than those for configuration I. Use of larger values of 6 for configuration II flows, as predicted

by equation (3) results in very good agreement between the results for the two

flows in both Figures 5c and 7c. However, as noted in Figure 4b, the values

of 6 determined from the experimental velocity profiles for configuration II

do not justify the use of the prediction made directly from equation (3).

Hence the fit in equation (3b) was used in preparing the curves involving

y/6 for configuration II flows.

OSCILLATING FLOW EXPERIMENTS

Two aspects of oscillating flows produced by the tunnel were examined.

The first dealt with the behavior of the mainstream oscillating flow and the

second focused on one case of oscillating boundary layer flow. These are

discussed separately below.

Mainstream Oscillating Flows

Previous experiments and theoretical analysis for mainstream flow for

the present type of facility operated in the oscillating flow mode have shown

that as frequency of oscillation increases from a low value, the amplitude of

oscillation U departs from uniformity with x and an x dependent phase difference denoted by 6 appears in the flow (Refs. 1, 2, 3). The velocity variation with position and time at a fixed frequency of oscillation can be written for the mainstream as

U(x,t) = U + U1(x)Cos[cut + 8(x)] (5)

o 1

U. (x) and 6(x) can be theoretically predicted from the following expressions.
10

= aS(x)

S(x) = {(BCosS + CCosnO2 + (BSin; - CSinnC)2}^ (5a)

„, ,. .. -l.BSin? -

6(X) = tan {BCosC +

where

1 - M

o

n =

C =

1 + M

o

a (1 - M )

In these expressions a is sonic velocity, M = U /a, and B and C are constants which are evaluated by use of two boundary conditions, the first of

which is obtained at x = H. The ratio of A« , the area at the nozzle entrance, to the sonic area A* varies as A* changes due to the motion of the

wedge. Neglecting the unsteady effects in the converging section of the

nozzle and using the relation between A/A* and Mach number for isentropic

flow, the Mach number variation S(&) can be obtained from the wave generator

geometry. The second boundary condition is obtained at x = 0. Unsteady

effects are neglected in the entrance section and through a pressure matching iterative procedure, the second boundary condition is imposed. Since

each boundary condition yields a relation between B and C, values for B

and C are obtained.

Experiments related to the behavior of the mainstream flow in the

present facility were conducted for frequencies ranging from 3 to 15 Hz.

Velocity measurements using the data acquisition system, Figure 2, were

made at x = 0.11 m and x = 2.48 m with the hot wire probe positioned

through instrument ports on the top wall 6.7 cm from the wall. The same

wave generator configuration was used for all oscillating flow experiments

and is designated as configuration III in Table 2. The value of S(£) for

this configuration is 0.012. Hotwire voltage values were read at 20 equally
11

spaced time intervals for each cycle of oscillation. An external trigger

to the voltmeter, Figure 2, was provided by the conditioned and amplified

signal from a magnetic pickup, part of which was mounted on a flywheel

fixed to the wave generator drive shaft. The shaft speed was controlled

within 0.02 percent and was monitored by a light-sensing pickup and an EPUT

counter. The 20 voltage readings per cycle were ensemble averaged over 100

cycles and converted to velocities by use of the hot wire calibration curve.

A sine wave was then fitted to the 20 ensemble averaged velocity values.

The resulting fits are of the form

U = UQ + u^CosCut - 3) (6)

where 3 is a phase angle. Figure 9a shows curves obtained in this manner

for two frequencies of oscillation at x = 0.11 m and x = 2.48 m. Equations

for the fitted curves are also shown. It is evident from the close proximity

of the ensemble averaged results to the fitted curves that on an ensembleaveraged basis, the velocity variation is sinusoidal. At a frequency of

3 Hz the amplitude of oscillation U at x = 0.11 m is slightly larger than

that at x = 2.48 m, but U and 3 at the two locations are essentially the

same. At 15 Hz, the results for the two positions show significantly different amplitudes of oscillation and exhibit a phase difference, with the

oscillation at x = 2.48 m leading that at x = 0.11 m.

Results like those in Figure 9a can be displayed more descriptively

in terms of S and 6 vs x, as shown in Figure 9b. Experimental results at

x = 0,11 m and 2.48 m as well as predicted variations for S and 8 are displayed. At the lowest frequency, f = 3 Hz , S is predicted to be essentially

constant with x at the value 0.012, indicating no significant variation in

U. with x. A small variation in 8 is also predicted. At higher frequencies, 15 Hz for example, larger variations in S and 6 are predicted. It
12

is evident in the figure that most of the experimental values of S are

larger that the corresponding predicted values. This can be seen more

clearly in Figure 9c which compares predicted and experimental variations

in S and 0 in terms of frequency for the two x locations. While the trend

for S is correctly predicted at x = 0.11 m, the variation in S indicated by

the measurements at x = 0.11 m exhibits a more pronounced increase with frequency. This is probably related to the fact that the theory on which the

prediction is based assumes that the facility has short entrance and subsonic

nozzle section lengths compared to the test section length £, a condition

that does not exist in the present facility. Values of S at x = 2.48 m

are larger than predicted values only for frequencies greater than 12 Hz.

Also, as shown in the figure, the experimental results for 9 at x = 2.48 m

agree well with the predicted variation for f > 10 Hz. Experimental values

in the remainder of the frequency range fall below the predicted curve.

'Apparently something not accounted for in the theory is taking place in the

flow near the test section exit to produce these results.

Oscillating Boundary Layer Flows

A boundary layer survey was carried out for oscillating flow at the

x = 1.66 m location on the top wall centerline at a frequency of 4.11 Hz

for flows produced by wave generator configuration III. The reduced frequency ol = wx/U for the flow produced is 0.96. Results at 12 values of y were

obtained and are tabulated in Table 3. Data were taken in the manner described for the mainstream oscillating flow experiments. The number of

cycles over which the 20 ensemble averaged velocity values were obtained is

listed in the table. Sine waves were fitted to the 20 ensemble averaged

velocity values for the cycle, yielding an equation of the form of equation
13

(6) at each of the 12 y values. The values of y/6, as listed in Table 3,

were obtained by dividing the y values by the steady flow boundary layer

thickness at x = 1.66 m as given by equation (3a) . Curves and the correponding equations for the velocity variations at the extreme values of y/6

in the survey are shown in Figure lOa. The ensemble averaged velocity

values closely fit the sine waves, even at the lowest value of y/6 at

which data were taken.

With the freestream as a reference, the expression for the velocity in

the boundary layer at a fixed x location can be written as

u(y,t) = u(y) + U(y)Cos[a)t + <t>(y)] (7)

In the freestream u = U , u- = U.. and <j> = 0. Values of u /U , u.. /U, and

<j> based on the listed values of U and U.. are tabulated in Table 3. Figure

lOb presents a comparison of mean velocity profiles in terms of u /U and

y/6. Shown are the steady flow profile at x = 1.66 m (Figure 5a) , the profile

for oscillating flows (Table 3) and the profile predicted by the numerical

9 10

method developed by Murphy . The Cebeci-Smith turbulence model was used

in obtaining the numerical predictions . Also, 6 as given in Table 3, was

used to form the y/6 values for the numerical predictions in this and other

related parts of Figure 10. The experimental oscillating flow velocity

profile in Figure lOb agrees well with the experimental steady flow profile.

However, the numerical method predicts values larger than the measured mean

values in most of the boundary layer.

Figure lOc compares the experimental profile for u /U, from Table 3

with the numerically predicted profile. The results are in good agreement.

Both indicate values of u.. /U, slightly larger than unity in a part of the

boundary layer. Figure lOd shows a comparison of experimental results for

the phase angle <j> from Table 3 with those predicted numerically. The results

*The numerical predictions in Figure 10 were provided by J. D. Murphy.
14

are in reasonable agreement down to y/6 = 0.2, after which experimental

values for <}> decrease while predicted values for <)> increase. The same behavior was observed for a case with nearly the same reduced frequency for

flows produced in a smaller-scale version of the present facility (Ref. 1).

Results for this case as well as the present results are shown in Figure

lOe. Since the same trend in experimental data was observed in both

facilities at nearly the same flow conditions, there is a strong indication

that the experimental behavior for <j> observed at low values of y/6 is correct.

In the ensemble averaging process to obtain velocity values turbulence

intensities were also computed at the 20 points in the cycle. Turbulence

intensities as given by equation (4) with u replaced by the local ensemble

averaged velocity were determined and a sine wave was fit to the 20 values

to obtain a mean value and range of the turbulent intensity variation.

Figure lOf shows a comparison of steady flow turbulence intensities and

the turbulence intensities for oscillating flow. It is evident from the

figure that except at values of y/6 greater than 1.1, the turbulence intensity for oscillating flow varies around a mean value equal to that for steady

flow.

Comments on Oscillating Flow Experiments

The experimental results for oscillating flows clearly show that the

mainstream velocity variation is sinusoidal for frequencies ranging up to

15 Hz. Further, the collective results for the mainstream oscillating flows

as shown in Figure 9 indicate for the most part that the flow behaves qualitatively as predicted by the theory in that at higher frequencies the amplitude of oscillation decreases with increasing x and a phase difference exists

between the downstream flow and the upstream flow, with the downstream flow

leading the upstream flow. The influence of this feature of the flow on
15

boundary layer experiments at high frequencies, while unknown, is expected to

be small. The ensemble averaged results for the oscillating boundary layer

flow case studied show that at any point in the boundary layer the velocity

oscillates sinusoidally around a mean value equal to that measured at the

same point in the steady flow boundary layer. Similarly, the turbulence

intensity for the oscillating flow varied around a mean value equal to that

for steady flow. The observed values greater than unity for the amplitude

ratio n /IL in the boundary layer are consistent with several other experiments. Also, the measured variation of phase angle for the case studied is

consistent with results from a previous study of a similar flow in a smaller

similar facility.

CONCLUDING REMARKS

Experiments performed to assess the flow in the 20 cm x 40 cm oscillating flow tunnel indicate that the facility produces good quality test

flows when operated in either the steady flow mode or the oscillating flow

mode. Results indicate that in steady flows, the mainstream velocity is

uniform in the flow direction and in cross section. The freestream turb-.r

ulence intensity is about 0.2 percent. With minor exceptions the steady

turbulent boundary layer generated on the test section top wall exhibits

the characteristics of a zero pressure gradient turbulent boundary layer

generated on a flat plate. For oscillating flows the mainstream velocity

variation is sinusoidal for frequencies up to 15 Hz, the highest frequency

studied. These flows behave qualitatively as predicted by theory. The

oscillating flow boundary layer case studied indicates that oscillating

boundary layer flows like those observed in other oscillating flow experiments are generated in the tunnel. In conclusion, the results of this

investigation indicate that the facility will provide an excellent experimental means of studying a number of aspects of viscous and inviscid

oscillating flows.
16

REFERENCES

1. Cook, W. J. "A study of turbulent boundary layers in oscillating flows,"

Iowa State University Engineering Research Institute Technical Report ISUERI-Ames-84408, 1983.

2. Cook, W. J. and Yamaguchi, Y. "A faciltiy for studying turbulent boundary

layers in oscillating flows," Iowa State University Engineering Research

Institute Technical Report ISU-ERI-Ames-82186, 1982.

3. Cook, W. J. "A faciltiy for producing periodic subsonic flows," Iowa

State University Engineering Research Institute Technical Report ISUERI-Ames-81117, 1980.

4. Smith, A. and Clutter, D. "The smallest height of rougness capable of

affecting boundary layer transition," J. Aero. Sci., 26 (1959): 229-245.

5. Westphal, Russell "VPRO, A computer code for steady boundary layer data

analysis," Private communication.

6. Coles, Donald "The young person's guide to the data," Poceedings, Computation of turbulent boundary layers, 1968 AFOSR-IFP-Stanford Conference,

Vol. II, Stanford, CA, August 18-25, 1968.

7. Charnay, G., Comte-Rellot, G,, and Mathien, J. "Development of a turbulent

boundary layer on a flat plate in an external turbulent flow," AGARD-CP-93,

London, U.K., Sept. 1971.

8. Schlichting H. "Boundary layer theory," 4th Edition, McGraw-Hill Book

Company, New York. P. S. Kelvanoff results, p. 467.

9. Murphy, J. D. and Prenter, P. M. "A hybrid computing scheme for unsteady

boundary layers," Third Symposium on Turbulent Shear Flows, University

of California, Davis. 1981.

10. Cebeci, T. and Smith, A. M. 0. "A finite difference solution of the imcompressibel turbulent boundary layer equations by an eddy-viscosity concept,"

AFOSR-IFP-Stanford Conference, 1968.
17

Table 1. Description of the 20 cm x 40 cm Oscillating Flow Tunnel.

See Figure 1.

Entrance Section

Flow-Straightening Section: Cross Section, 0.62 m x 1.22 m

Length = 0.64 m

Test Section

Contraction Section:

Length = 2.75 m

Cross Section:

Entrance,

Exit,

Length = 1.22 m

Area Ratio = 9 to 1

Honeycomb: 0.32 cm Hex Cell x 2.54 cm

Screens (Listed in direction of Flow)

Mesh per inch Porosity, %

10 64

20 64

30 60

Width

40.6 cm

43.8 cm

Material: 2.54 cm thick Plexiglas

Wave Generator

Length = 0.94 cm

Nozzle Throat Blocks:

Throat Cross Section,

Throat Area,

Set A Set B

10.2 cm x 20.3 cm 5.08 cm x 20.3 cm

207 cm' 103 cm

Wedge: 20 Included Angle, 5.08 cm Stroke

Oscillator Frequency: Zero to 15 Hz

Boundary Layer Trips

0.63 mm diameter wires on four walls at test section entrance.
18

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20

External trigger,

one per cycle

DISA 55M10

Anemometer

Unit

t

DISA 55D10

Linearizer

1

Hewlett

Packard

3437A A/D

Vol tmeter -

Commodore

computer

system,

machine

language

programmed

Probe positioning

mechanism

Test section

wall

Flow DISA P14 Single-wire probe

Figure 2. Data Acquisition System.
2

1

S 5I

I

D<3 O I ' I i! i

</> LUO

coo0)tn<o

(fl o

4-1 ^ o e

4-1 r—

1-1 •

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\-t 0)

u > M cd C S •HCO6 j O 00 •H 00

4-1 > O .H 01en u enO> 1-1 H co 300
22

SOLID SYMBOLS: Config. I

OPEN SYMBOLS: Config. II

0 I I | I I I i i i I I I

0.5 1.0 1.5

x, m

2.0

12

10

10"3Ren

2.5 i

a. Variation of ReQ, Cr, and H with x.

0 I

Figure 4. Boundary layer quantities for steady flows produced by wave

generator configuration I, UQ = 45.7 m/s and configuration II,

U0 = 26.6 m/s.
23

6, cm

Measured values

O Config. I

D Config. II

Predicted variation, Eq. (3),

Config. II

5, cm = 2.10(x, in)0"®

V

1

Config. I, Eq. (3a)

6, cm = 1.888(x, m)0'

8

Config. II, Eq. (3b)

6, cm = 1.72(x, m)0-

8

t i i i i i

0.5 1.0 1.5

x, m

2.0 2.5

b. Comparisons of predicted and experimental velocity boundary

layer thicknesses.

Figure 4. Concluded.
24

1.5

6

1.0

0.5

0

Symbol x, m

o 0.44

* 0.74

+ 1.35

x 1.66

A 1 .88

0 2.48

—

—

--^-tf*

0.4 0.6 0.8

XoA

u/U.

1.0

a. Configuration I. U0 = 45.7 m/s.

Figure 5. Steady flow velocity profiles.

1.2
25

1.5

*

1.0

0.5

n

1 '

Sybmol x, m

o 0.44

A 1.35

0 2.48

-

—

1 *•*£•

~l

" 0.4 0.6 0.8 1.0

u/Uo

b. Configuration II. U0 = 26.6 m/s.

Figure 5. Continued.

1.2
26

2.0

1.5

X.

&

1.0

0.5

i

Symbol x, m Config,

° 1.35 I

* 2.48 I

A 1.35 II

- 2.48 II

I

•+. o

A n

0.4

4*

0.6 0.8

u/U,

1.0 1.2

c. Comparison of profiles for configurations I and II.

Figure 5. Concluded.
27

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O

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x

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28 ORIGINAL PASS-8S

POOR QUALFTY

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29

ORIGINAL PAGE'IS

OF POOR QUALfTY

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32

2.0

Symbol Position at x = 1.88 m

o 11 cm Right of C

1.5

y.6

1.0

0.5

0

T~

11 cm Left of C

0

0.4 0.6 0.8 1.0 1.2

u/U

o

a.

Figure 8. Experimental results for three boundary layer surveys

at x = 1.88 m.

(See Figure 3 for left and right designations.)
33

O "•-.

Q-3

U*|

a '

_!. j j _

a

a

a

a

00

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OF

 POOR

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jr

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a

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<1

C;- —

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10

a S ^H +j

O)

o

d)

Kin

0 <J

0-

(U

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y

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in

o

oo

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3

00

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55

50

U, m/s

45

40

35 -

30

35

15 Hz

ID,

Equations for fitted curves

f = 3 Hz

x=0.11 m: U=44.92+4.323Cos (iot-1.242)

x=2.48 m: U=44.68+4.05 lCos(iut-1.239)

f = 15 Hz

x=0.11 m: U=44.81+8.003Cos(ujt-l.597)

x=2.48 m: U=44.78+4.830Cos(ut-l.399)

Ensemble average, 100 cycles

x=0.11 m,

3 Hz

x=2.48 m,

3 Hz

i ' ' j 1 i J 1 '

TT/2 3n/2 2n

(at

a. Velocity variations at x = 0.11 m and x = 2.48 m for two frequencies.

Figure 9. Results for mainstream oscillating flows.
0.024

0.020

0.016

S =

0.012

0.008

0.004

_ 0

36

I 1 T

Experiment

f, Hz

Prediction

O

D

A 7.5

ORIGINAL PAGE 13

OF POOR QUALITY

1 T

15

9, degrees

10

2.4 i 2.8

b. Comparisons of experimental and predicted S and 8 variations

in terms of x.

Figure 9. Continued.
3

7

<u

<uS- 01

m .

- o

a

OJ

E E 00 00

O CM CM

o n o

•ac

cfl COCO•H4J

cfl •H

1-1

Cfl T3OJ

4-1 • o X •H-O 4-1 CU O CX COOl 13 3 C .-I CO cfl rH

cfl O C 4J 0) 6 t-i •H O CDX O 0) C0)

Ml ^j o cr cu CO J-i C >4-l OCO M-l •H O

Cfl CO

a 6 O Q)

T3

<UOCoo

CVJ o

o

(\Joo

oo

CM

r—t oo

00oo

oo

Doo •H
3

8

oCO3rH

cfl 0) Q)

t-i

4-1XQ) 0)do•HiJ

cfl •H

S-l a) •HOO

•a3n) •ado8ao 6 c•H >£>

Jl VD

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a

QJ

S-i 300 •H
39

2.0

1.5

y

6

1.0

0.5

0.4

Experiment, Steady flow

Experiment, mean value,

Oscillating flow

Numerical prediction

0.6

O

o

O

a

O

o

c^

1 O

O

°0

0.8 1.0 1.2

b. Comparison of mean velocity profiles.

Figure 10. Continued.
2.0

1.5

y.6

1.0

0.5

• Experiment, oscillating

flow

D Numerical prediction

-•BOG

a

a

a

I

0.4 0.6 0.8 1.0

V

U

1

c. Comparison of amplitude ratio profiles.

1.2

Figure .10. Continued.
I 1 I

• Experiment,

oscillating flow

O Numerical prediction

0 I 1 1 1 1 U04 1 1 1- -0^oJ

2.0

1.5 -

y_

&

1.0 -

0.5 -

Present results

• Experiment

O Numerical prediction

Case El. Ref. 1

f=5.04 Hz, x=1.58 m,

, u1/UQ=0.126

Experiment

Numerical prediction

d. Comparison of phase angle profile s e. Comparisons of results for phase

angle for two flow cases.

Figure JO. Continued .
a

f\J

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«l

Irt

2

0

4—

2 01 01 -r

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•— ••- C _

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to

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>> rTD r03 T:? I « ' .?

Ol O ro U

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(/> O O> c

+-> 4-> ro O

c c > C

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to ^

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