Design and Development of a Deep Acoustic Lining for the 40-by 80-Foot Wind Tunnel Test Section

The result of this technically ambitious project has been Concluding Remarks the creation of a unique acoustic wind tunnel. Its large test The work described in this report has made effective use section (39 ft x 79 ft x 80 ft), potentially near-anechoic of design teams to build a state-of-the-art anechoic wind- environment, and medium subsonic speed capability tunnel facility. We evaluated many potential design solu-

(M = 0.45) will support a full range of aeroacoustic

tions using engineering analysis and computational testing-from rotorcraft and other vertical takeoff and tools. Design alternatives were then evaluated using landing aircraft to the takeoff/landing configurations of specially developed testing techniques. Large-scale both subsonic and supersonic transports.

coupon testing was then performed to develop confidence that the preferred design would meet the acoustic, aerodynamic, and structural objectives of the project.

Finally, designs were frozen and the final product was installed in the wind tunnel.

APPENDIX

PREDICTION METHODS FOR SOUND ABSORPTION OF ACOUSTIC LININGS

Current methods for predicting the sound absorption qualities of porous materials cannot model the complete wind- tunnel lining comprising the porous face sheet, screen, perforated wall grating, and fiberglass wedges. However, some components can be modeled, and the predicted performance gave credibility to the experimental methods described in this report.

Part A. Bulk Fiberglass Absorption: Low Frequency

Mechel and Ver (ref.9) employed regression constants from experimental data to compute the impedance and sound absorption of fibrous materials; we used them to predict the low-frequency sound absorption of certain 4Ox80 acoustic linings. The normal incidence absorption coefficient for a large flat absorber without covering and placed against a hard surface is given by 4Z1Z0 (6) where an is the acoustic energy absorption coefficient (ratio of absorbed and incident energy) ZI is the normal specific lining impedance ZI and ZI' are the real and imaginary components of ZI

Zo = Poco is the characteristic impedance of air

and P

ZI = ZO[(1 + b'E-P') - jb''E- ''] coth (rll d) (7)

The complex propagation constant is a

P

r = koa'E- ' + j( 1 + a''E- ")

(8)

ll

where d is the lining depth

E = Pof I R 1 is a normalized frequency parameter

fis the frequency, Hz RI is the lining flow resistivity, mks rayls/m

ko = ro I Co = 27tf I Co is the acoustic wave number in air

and a',a",a',a", b', b",j3',13" are regression constants from table 8.2 in reference 9, which are reproduced below for minerallbasalt wool and fiberglass.

Regression Constants a' a" b' b" Material E region a' a" j3'

13"

MineraVbasalt ESO.025 0.322 0.502 0.136 0.641 0.081 0.699 0.191 0.556 Wool E > 0.025 0.179 0.663 0.103 0.716 0.0563 0.725 0.127 0.655 Glass fiber E ~ 0.025 0.396 0.458 0.135 0.646 0.0668 0.707 0.196 0.549 E > 0.025 0.179 0.674 0.102 0.705 0.0235 0.887 0.0875 0.770 The above equations were coded to give the prediction curve in figure 9(a), which agrees well with impedance tube data for a 36-in.-deep OCF 701 bulk fiberglass lining with a density of 24 kg!m and a flow resistivity of 6,000 mks raylslm. Unfortunately, the prediction for OCF 703 (48 kg! m\ 27,000 mks raylslm) differed considerably from the measured sound absorption. The computer code follows.

1* MV_absorp.c 217/97 PaulT.Sodennan

*

NASA Ames Research Center

*

* Think C compiler (ANSI C) for Macintosh

*1 1***************************************************** ***********************************************

*

* Program computes nonnal incidence sound absorption of bulk material based on the * empiricial curve of Mechel and Ver (Noise and Vibration Control Engineering.

* Beranek and Ver, ed. Ch 8 Mechel and Ver.

* This code is commented to be ISO 9000 compliant. The author does not guarantee accuracy

* of the results nor that the code will run under all conditions.

*

******~*********************************************** ***********************************1 #include <math.h> #include <stdio.h> #include <string.h> #include <time.h>

#include <console.h> 1* needed for output redirection using Think C and Mac *1

#define NFREQ 36 1* number of frequencies *1

float alpha[NFREQl = (O); 1* array of sound absorption coeffs *1

char file_name[30]; 1* string array of file name *1

typedef struct

double depth; 1* lining depth, m *1

double resist; 1* lining resistivity, mks raylslm *1

) linin~t;

1* function prototypes *1

void alpha_calc( linin~t, float*, long int* ); void data_out( linin~t, float*, long int* ); int make_file( linin~t, char*, float*, long int* ); int princfile( char* ); void skip_line( void ); linin~u lining; int mainO { char menu( char ),

i = 'I " 1* menu number *1

**dummy; 1* dummy argument for access to I/O *1 char *ptcfile_name; 1* pointer to file name string *1 long int *ptcfreq; 1* pointer to freq array *1 float *ptcalpha; 1* pointer to alpha array *1

int count = 0, 1* record counter *1

printout = 1; 1* printer control constant *1

long int freq[] = {25,31 ,40,50,63,80, 100, 125, 160,200,250,315,400,500,630,800, 1000,1250,1600,2000,2500,3150,4000,5000,6300,8000,1 0000,12500, 16OO0,2oooo,25ooo,315oo,40000,5oooo,63ooo,80ooo} ; 1* third oct center freqs *1

ptr_freq = freq; 1* initialize pointers *1

ptr_alpha = alpha; ptr3i1e_name = file_name; while ( printout) { i = menu( i); switch ( i ) { case '1': 1* Call absorption calc routine and absorption array *1 printf( "\oCalculate sound absorption\o" ); printf( "\t%s", "Input lining depth, m " ); scanf( ''%If', &lining.depth ); printf(" \o\t%s", "Input material flow resistivity, mks rayls/m " ); scanf( ''%If', &lining.resist ); alpha_calc( lining, alpha, freq ); make_file( lining, ptcfile_name, alpha, freq ); break; case '2': data_out( lining, alpha, freq ); break; case '3': printf("\t %s \n", .. choose file as standard input "); printf("\t %s \n", .. and console+printer for standard output "); printf("\t %s \n \n", "hit return to start and finish this operation "); scanf("%c", &i); ccommand ( &dummy );

1* dialog box arid 110 redirection options *1

1* must be last after declarations *1

break; case '4': exit (1); break; return 0; 1***************************************************** *********************************************** Function menuO creates menus for user input and output manipulation.

***************************************************************** * **********************************~ char menu ( char ch ) ( printf( "\n\n%s\n","NASA Ames Research Center"); printf( "%s\n","Record Database" ); printf( "%s\n \n","Enter One Selection 1 - 4" ); printf( "\t%s\n"," 1 - Input data, calculate results, make file" ); printf( "\t%s\n","2 - Display results on screen" ); printf( "\t%s\n","3 - Print output file and exit" ); printf( "\t%s\n","4 - Exit program" ); ch = getchar(); return ch; 1***************************************************** *********************************************** * Function alpha_calc computes sound absorption of a bulk liner against a hard surface.

* Normal incidence sound is assumed. The alpha array is filled.

*

****************************************************************************************************~ void alpha_calc( linin~t lining, float *ptr_alpha, long int *ptr_freq ) ( const float rho = l.225, 1* air density, kg/cu m *1 co = 340.0, 1* sound speed, mls *1 pi =3.141593, 1* pi *1 zo = 416.5, 1* char impedance of air, mks rayls *1 ap1 = 0.396, 1* regression constants for fiberglass *1 ap2 = 0.179, 1* table 8.2 *1 alfap1 = 0.458, alfap2 = 0.674, app1 = 0.135, app2 = 0.102, a1fapp1 = 0.646, alfapp2 = 0.705, bpI = 0.0668, bp2 = 0.0235, betap 1 = 0.707, betap2 = 0.887, bpp1 = 0.196, bpp2 = 0.0875, betapp1 = 0.549, betapp2 = 0.77; const double e = 2.1718282; double ko, 1* wave number in air * 1 efreq, 1* MV frequency constant *1 gama_real, 1* propagation constant, real comp *1 gama_imag, 1* propagation constant, imag comp *1 zan_real, 1* matI char impedance, real comp *1 . zan_imag, 1* matI char impedance, irnag comp *1 zIn_real, 1* lining impedance, real comp *1 zln_imag; 1* lining impedance, imag comp *1 int i, 1* loop counter *1 first = 1, 1* complex number flags *1 second = 2; long int ifreq; 1* frequency parameter *1 double complex_hypeccot( double X, double Y, int flag ); for (i = 0; i < NFREQ; i++, ptr_alpha++, ptrjreq++) { ifreq = *ptr_freq; ko = 2.0 * pi * ifreq 1 co; efreq = rho * ifreq 1 lining. resist; if ( efreq <= 0.025 ) ( gama:..real = ko * apil pow( efreq, alfap1 ) * lining.depth; gama_imag =( l.0 + appll pow( efreq, alfappl » * lining.depth; zan_real = l.0 + bpi 1 pow( efreq, betapl ); zan_imag =- bppll pow( efreq, betappl ); else gama_real = ko * ap2 1 pow( efreq, alfap2 ) * lining. depth; gama_imag = ( 1.0 + app21 pow( efreq, alfapp2 » * lining.depth; zan_real = 1.0 + bp21 pow( efreq, betap2 ); zan_imag =- bpp2 1 pow( efreq, betapp2 ); *ptcaipha 1= « zln_real + l.0) * ( zln_real + l.0 ) + zln_imag * zln_imag ); ) return; 1***************************************************** *********************************************** * Function complex_hypeccot computes the re,al and imaginary values of the hyperbolic * cotangent of a complex number. The real or imaginary components are returned depending * on the flag sent to the function: I for real, 2 for imaginary.

*

**************************************************************************************************** double complex_hypeccot( double X, double Y, int flag) double a,b,c,d,

1* parameters abed for coth ratio *1

value,

1* return value (real or imaginary) *1

el;

1* parameter for exp(x) *1

el = exp( X); a = e I * cos( Y ) + cos( Y ) 1 e I ; b = e I * sine Y ) - sine Y ) 1 e I ; c = el * cos( Y) - cos( Y) 1 el; d = e I * sin( Y ) + sin( Y ) 1 e I ; if( flag = I ) value = ( a * c + b * d ) 1 ( c * c + d * d); else value = ( b * c - a * d ) 1 ( c * c + d * d ); return value; 1***************************************************** *********************************************** * Function make_file creates a file of frequencies and computed absortion coefficients.

**************************************************************************************************** int make_file( linin~t lining, char *ptr3ile_name, float *ptr_alpha, long int *ptr3req ) int i; time_t now; struct tm *date; char s[80]; FILE *fp; now = time( NULL ); date = localtime( &now ); strftime( s, 80, "%x", date ); strcat( file_name, s ); printf( "\o\t%s\o" ,"make file" );

if ( (fp = fopen(file_name, "w"» = 0 )

( printf( "cannot open file %s to write\o",file_name ); return 0; fprintf( fp, "\0\0 %s ", file_name); fprintf( fp, " \t%s ", " P. Soderman "); strftime( s, 80, "%a, %b %d, %Y %H:%M", date); fprintf( fp, "%s\o", s ); fprintf( fp, " \t %s %3.lf %s \0 ", "fiberglass depth = ", lining.depth, "m"); fprintf( fp, "\t %s %3.lf %s \n \n ", "resistivity = ", lining.resist, "mks rayls/m" ); fprintf( fp, " \t %s \n ", " Absorption coefficient (normal incidence) " );

for ( i = 0; i < NFREQ; i++, ptrjreq++, ptr_alpha++ )

fprintf( fp, "%5Id %6.4f%c ", *ptrjreq, *ptcalpha, (i%5=411 i=NFREQ-l ? '\n': "»; fclose( fp ); return 1; 1***************************************************** **********************************************' * Function princfile prints file created by make_file to standard output **************************************************************************************************** int princfile( char *ptr_file_name ) { FILE *fp; int c; if ( (fp = fopen(file_name, "r"» = 0 ) ( printf( "cannot open file %s to read\n",file_name); return 0;

while( (c = fgetc(fp) ) !=EOF)

putchar( c); fclose( fp ); return 1; 1***************************************************** *********************************************** * Function data_out prints computed output to screen *********************************************************************:~****************************** void data_out( linin~t lining, float *ptr_alpha, long int *ptrjreq ) ( int i; printf(" \n \n \t %s ", " Sound Absorption - normal incidence "); printf(" \t \t %s \n ", " P. Soderman "); printf(" \t %s %3.lf%s \n ", "fiberglass depth = ", lining.depth, "m"); printf( "\t %s %3.1f %s \n \n ", "resistivity = ", lining. resist, "mks rayls/m" ); printf( " \t %s \n ", .. Absorption coefficient (nonnal incidence) " );

for ( i = 0; i < NFREQ; i++, ptr_freq++, ptr_alpha++ )

printf(" %51d %6.4f%c", *ptr3req, *ptr_alpha, (i%5 411 i=NFREQ-l ? '\n': "»; return; 1***************************************************** **********************************************' * Function skip_line reads and ignores a11 characters up to and including the first new-line * ~haracter. Use to clear input buffer.

**************************************************************************************************** void skip_line( void) " ( while( getcharO != '\n' ) " , ) Part B. Analytical Model of Plate and Lining: High Frequency Wilby and Wilby (ref. 18) evaluated a number of analytical models for the absorption of sound by porous materials spaced behind a perforated facing. The predictions were then compared with data from the high-frequency pulse test series. None of the models account for a grating between the facing and lining.

It is assumed that the acoustic impedance of a perforated plate can be taken in series with that of a backing lining.

(9)

~ = ~l + ~p = '6 + iX

where ~ is the total specific acoustic impedance nonnalized by Poco ~l and ~p are the nonnalized specific impedance of the back lining and perforated facing, respectively, and '6 and ~ are the real and imaginary components of ~.

Wilby and Wilby found that the real part of the nonnalized specific impedance of the back lining was essentially 1 and that the imaginary part was essentially zero (ref. 18). Furthennore, the impedance of a perforated plate located some distancj;: from the back lining is dominated by the reactance. Thus, equation (9) simplifies to: (10) and the absorption coefficient is given by (11) Thus, it is necessary to obtain a relationship for Xp' Guignouard et al. (ref. 23) give the following expression for reactance of a perforated plate: (12)

Xp = (kO I p)(t + 25)

where

P = open area ratio

t = plate thickness

d = petforation hole diameter

and the end correction for a hole is

5 = 0.24d( nO.s - 2.5PO ' S) (13)

which is taken from Ingard (ref. 28), but becomes negative for P > 0.503.

In another work from Ingard (ref. 29), the end correction is given as (14) where F(P) is described graphically and decreases as P increases so that F(P) = 0 when P = I. This and other representations of end correction are illustrated in figure 52.

0.5 0.45 0.4 "- Q) 4) 0.35 E

a 0.3

CI.J '00.25 -.-Ingard, circle in circle (ref. 28) :::c .......

---a-Ingard, circle in square (ref. 28)

§ 0.2

-o-Ingard (ref . 29) ' +:;j ---'&-Mechel & Ver (ref. 9)

~ 0.15

o

u 0.1

'"0 c:: LLJ 0.05

o

o 02 0.4 0.6 0 .8 1

Open Area Ratio, Figure 52. Comparison of end corrections for holes in a perforated plate (from ref. 17).

In addition to the above expressions for bulk absorbers, Mechel and Ver (ref. 9) have published two models for impedance of a perforated plate. One, according to Wilby and Wilby (ref. 18) is equivalent to equation 12. The second gives the impedance of perforated plate resonator covers exposed to various sound pressure levels and grazing flow speeds. For low sound pressure levels and zero flow: (15) where v is the kinematic viscosity of air and the appropriate end correction is

5 = 0.425dcjl(P) (16)

where

cjl(P) = 1-1.47po.5 + 0.47p1.5

(17) Figure 49 shows a comparison of measured sound absorption by Wilby and Wilby (ref. 15) with the above predictions of Guignouard et al. (ref. 23), Ingard (ref. 28), and Mechel and Ver (ref. 9). The Guignouard model agrees best with the data, particularly for the 16 gauge, 68%-open perforated plate.

Report No. 7739 (NASA Contract NAS2-13461),

References

Sept. 1992.

1. Soderman, P. T.; Jaeger, S. M.; Hayes, J. A.; and 11. Dunn, I. P.; and Davern, W. A: Calculation of Allen, C. S.: Acoustic Performance of the 40- by 80- Acoustic Impedance of Multi-layer Absorbers.

Foot Wind Tunnel Test Section Deep Acoustic Applied Acoustics, vol. 19, 1986, pp. 321-334.

Lining. AIAA Paper 2()()().1939. 6th AIAAlCEAS Aeroacoustics Conference, Lahaina, Hawaii, June 12. Berhault, J. P.; Sunyach, M.; Arbey, H.; and Comte- 2000.

Bellot, G.: Realisation d'une chambre anecholque

revetue de panneaux et destinee a l'etude des bruits

2. Soderman, P. T.; Jaeger, S. M.; Hayes, J. A.; and d'origine aerodynamique (Design and Construction of Allen, C. S.: Acoustic Quality of the 40- by 80- an Anechoic Chamber Lined with Panels for Foot Wind Tunnel Test Section After Installation of a Investigation of Aerodynamic Noise). Acustica, Deep Acoustic Lining. NASAITP-2002-211851.

vol. 29, no. 2, 1973, pp. 69-78 (in French).

3. Soderman, P. T.: Sources and Levels of Background 13. McCormick, D. C.: Aerodynamic Performance of Noise in the NASA Ames 40- by 80-Foot Wind Candidate Acoustic Linings for the NFAC 40x80-Ft Tunnel: A Status Report. NASA TM-l00077, May Wind Tunnel. UTRC R93-970413-1, Aug. 1993, 1988.

contract NAS2-13605.

4. Schmitz, F. H.; Allmen, J. R.; and Soderman, P. T.: 14. Bauer, A B.: Acoustically Transparent Walls for Modification of the Ames 40- by 80-Foot Wind Aeroacoustic Wind Tunnel Applications. AIAA Paper Tunnel for Component Acoustic Testing for the 76-92, AlAA 14th Aerospace Sciences Meeting, Second Generation Supersonic Transport. 7th Washington D.C., Jan. 1976.

European Aerospace Conference, Toulouse-Labege, France, Oct. 1994.

15. Wilby, J. F.; White, - P. H.; and Wilby, E. G.: Pulse Reflection Study of Acoustic Lining Coverings.

5. Soderman, P. T.; Schmitz, F. H.; Allen, C. S.; AARC Report 137 (NAS2-13459), Atlantic Applied Jaeger, S. M.; Sacco, J. N.; and Hayes, J. A.: Design Research, May 1992.

of a Deep Acoustic Lining for the 40- by 80-Foot Wind Tunnel Test Section. AIAA Paper 99-1938, 5th 16. Wilby, J. F.; and Wilby, E. G.: Lining Reflections at AIAAlCEAS Aeroacoustics Conference, Seattle, High Frequencies: Progress Report for Phase I. W A Wash., May 10-12, 1999.

Report No. 103, (NAS2-13605), April 1993.

6. Soderman, P. T.; and Mort, K. W.: Aeroacoustic 17. Wilby, J. F.; and Wilby, E. G.: Lining Reflections at Characteristics of a Large, Variable-Pitch Fan High Frequencies - Phase II . WA Report No. 104, System. Proceedings for Inter-Noise 83, vol. 1, (NAS2-13605), Aug. 1993.

Edinburgh, Scotland, July, 1983, pp. 123 - 125.

18. Wilby, J. F.; and Wilby, E. G.: Lining Reflections at 7. Hayes, J. A.; Allen, C. S.; Soderman, P. T.; and High Frequencies - Phase IIA W A Report No. 105, Jaeger, S. M.: Test Techniques and Instrumentation (NAS2-13605), Sept. 1993.

for Acoustic Studies in Wind Tunnels. ISA 41st 19. Wilby, J. F.; and Wilby, E. G.: Lining Reflections at International Instrumentation Symposium, Denver, High Frequencies - Phase III . W A Report No. 106, Colo., May 1995.

(NAS2-13605), Nov. 1993.

8. Ver, I. L.: Initial Acoustical Design Study for 20. Wilby, J. F.; and Wilby, E. G.: Lining Reflections at Improving the Free-Field Acoustic Simulation High Frequencies - Phase lIB. W A Report No. 107, Performance of the Test Section of the NASA Ames (NAS2-13605), Jan. 1994.

Full-Scale Wind Tunnel. Contract No. FF 8024, BBN Systems and Technologies Corp, July 1988.

21. Wilby, J. F.; and Wilby, E. G.: Lining Reflections at High Frequencies - Phase IV. WA Report No. 108, 9. Mechel, F.; and Ver, I.: Sound-absorbing Materials (NAS2-13605), July 1994.

and Sound Absorbers. Ch. 9 in Noise and Vibration Control Engineering, L. Beranek and I. Ver, eds., 22. Wilby, J. F.; and Wilby, E. G.: Reflections of High- John Wiley & Sons, Inc., 1992.

Frequency Sound from Perforated Plates with Diffusion-Bonded Screens. W A Report No. 126, 10. Ver, I. L.; and Howe, M. S.: Acoustic Lining Study (NAS2-13605), Sept. 1993.

for the 40- by 80-Foot Wind Tunnel. BBN Systems 23. Guignouard, P.; Meisser, M.; Allard, J. F.; Rebillard, 26. Pierce, A. D.: Acoustics - An Introduction to Its P.; and Depollier, C.: Prediction and Measurement of Physical Principles and Application. Ch. 10, Effects the Acoustic Impedance and Absorption Coefficients of Viscosity and Other Dissipative Processes, at Oblique Incidence of Porous Layers with Perforated McGraw-Hill Book Co., N.Y., 1981.

Facings. Noise Control Engineering Journal, vol. 36, 27. Soderman, P. T.: Design and Performance of no. 3, May-June, 1991, pp. 129-135.

Resonant-Cavity Parallel Baffles for Duct Silencing.

24. Cops, A; and Myncke, H.: Determination of Sound Noise Control Engineering, vol. 17, no. I, July- Absorption Coefficients Using a Tone-Burst August 1981, pp. 12-21.

Technique. Acustica, vol. 29, 1973, pp. 287-296.

28. Ingard, U.: On the Theory and Design of Acoustic 25. Soderman, P. T.: Oblique Incidence Sound Resonators. J. Acoust. Soc. of Amer., vol. 25, no. 6, Absorption of Porous Materials Covered by Nov. 1953, pp. 1037-1061.

Perforated Metal and Exposed to Tangential Airflow.

29. Ingard, U.: Perforated Facing and Sound Absorption.

Inter-Noise 82, Proceedings vol. II, San Francisco, J. Acoust. Soc. of Amer., vol. 26, no. 2, Mar. 1954, Calif., May 1982, pp. 401-404.

pp. 151-154.

40,80 ~ 80,120 -'''''-------llIle,haust Figure 1. National Full-Scale Aerodynamics Complex Figure 3. NFAC plan view.

(NFAC).

Figure 2. 40xBO test section showing the 6-in. (152-mm) Figure 4. The six variable speed, variable blade-pitch deep absorbent wall lining prior to demolition and drive fans; each fan is 40 ft (12.2 m) in diameter.

installation of the deep lining; view looking downstream.

lining installation overhead crew door ~'-->

~ /

area wedge modules Figure 5. VOrlex generators in 40xBO diffuser inlet; view looking upstream.

(a) Far view.

680/. open perforated face sheet 12 lIB steel fine mesh metal screen ~~~_ floor grating ~ __ support structure pressure shell (bottom) shallow diffuser lini nn (b) Floor comparlment detail.

Figure 6. Uning location in wind tunnel. Figure 7. Four-foot-square modular comparlments that contain wedges and f10wllinlng interface.

porOlS interl ....

single bulk layer fiberglass (flow swI .... ) mulli.fayer bulk fi berglasl f ibergla8&!l1 HI wool fiberglass wedges _tical layers· PU.

... ...

r- r""O I"" r""O r""O

""I

T

['-.

\ ,07 m typical ....

['-. ['-.

r-- ,-' ...., ( .....

Ir-' lr lr

l

'II 'II

' "

preaur. walt '"

Figure B. Four conceptual designs considered for the 40xBO lining 10 cgs porous metal cover (Brunswick 347-1 0-30AC3A) #0 medium fine steel wool 39 in : : ~ ""!~~ .. ,,, .............:............. .,) ............. ;. ............ .

0 . 9 OCF 711

t .. ·······+-t;···~-t=·=+-·

..... ······i·············!· _33 In. anechotc wedge (Eckel)

i J. -11-39 In. PLL (11b.rgIa88l .... , wool lay.rs) i / i __ 36 In. bulk fiberglass (OCF 711 ) .. - ....... .; ..... , ...... ~. ___ 36 In. bulk flberglaas (OCF 703) i , i --emplrtcat 36 I n. OCF 711 (Mech., & V.r )

r i ---.mplrlcat 3B In. OCF 703 (Mech., & V.r )

0.5 o 200 400 800 800 1000 1200 12 in frequency. Hz (b) Perpendicularly layered lining (PLL).

(a) Absorption coefficients Figure 9. Performance of four candidate uncovered linings as measured in a 12-in.-square impedance tube (ref. 8).

The fiberglass wedge composition was not determined. The bulk fiberglass was installed in 2-in. layers stacked parallel to the tube. A typical PLL geometry is shown in figure 9(b).

0 .9 0.9 0.8 0.8 0.7 0.7

. . -medfine

c ~ .. .

.. . c ~

Ql Ql 0.6 ......... !' ....... ~ ........ : ........ ! ........ : -a-med coarse Ql Ql - u 0.6 .2c - u .2 c ;:Ql ~ E E E E -.-coarse ::: Ql : : : : :L..--WIIJ'II!I'I'I"""!"",,,q.

~:!2 0.5 Ql"C 0.5 u~ 8~ L.1n RI . NlX n..tled .. aln ...

. : g iii 0.4 rnka relytl m ..... ": ....... -: ...... ......... .

g iii 0.4 FICIiI' , .... uv "y: E.E ;::E 13 .5 32S mka raylslrn e.

o ~ ~ 0.3 g.s 0.3 :: :: .. ~:~M+·· .. ··l···· ..

.c as ~ 0.2 ..... f' ....... , ..... .

0.2 0.1

·· .. ·i· ...... ·~ .... ·· 0.1

o o 100 200 300 400 500 600 700 800 900 1000 o 100200 300 400 500 600 700 800 9001000 frequency, Hz frequency, Hz (a) Steel wool of various coarseness. (c) Needled stainless steel felt.

[ . . . . . . .

0.9 ...... ~ ....... ....... .

0.9

!j IIT r ····· _······ ·· ·

0.8

r1; :11 1]]

0 . 8 c ~ Ql Ql _ u

is 15

_wedge only l.. ... ... L Ql :!2 0.7 0 .7 · ·· ····j.······ ··I ········ 1 T Mmwlla sDver, j ..... .

o u u.s f 1 35 micron. 64 kg! m3 1 c- : : . 01. 550 mkl raylslm : o as

::': -1: '"

E. E 0.6 ······ ·: .. ······· : ········ r r ·· ··· · 0.6 ... 0 o c .!-

: ~ i !

as ! iii i

1 1 . !'

0.5 ···· ···i····· ··· -f· ····· ·+ ······· +·· ·· ··· ·! "ConIlg 4: 0.5 ······ T ····· ·r ······] , ...... .

: : : : : baaaline .

: : : : : CD' 71 3 nberglass wedge ..

! ! ! ! ; Manovlle _ (2 IbIcu ,6 0.4 0 . 4i-~+-~~-i~-r~~--~--r-~~-+~-r o 100 200 300 400 500 600 700 800 900 1000 o 100200 300400 500600700 8009001000 frequency. Hz frequency, Hz (d) Manville sliver fiberglass packed around a wedge.

(b) Manville sliver fiberglass.

Figure 10. Low-frequency absorption of single-layer bulk material. (Note variation in material depth.)

0.9 0.8 c~

-

CD CD :§g :Z:CD ~:2 0 .7 CJ .~ c_ 01\1 'E.~

o g 0.6

1:- 1\1 0 . 5

o 100 200 300 400 500 600 700 800 900 1000

frequency, Hz (a) Layers of fiberglass and steel wool.

0 . 9 ...... ·I ........ · ; .... .... r ...... ·I ........ 1" ...... ·' ........ r .... .. 1" ...... T ......

0 . 11 ~ PLL2 Ino lacIng) -0- PLL2+lIbermelal lacing 100 mila rayls ~ , la ci ng : -<>- PLL2+51 '" perf facing. 20 ga. 3/16 In holes ..... .. : ........ ..:. . . . 25mm .. t •• urder 0 . 8 0.8

: i 2Oga~ '*'

........ ::1' ...... . ~ opI k:tnaJ c_

i-

• u

i 'acing . ~ ; j U_"

- 3 .l! c lei :I: • 0 .7 .:2 11 0.7

8~ :; y u . ~

c_ 8, I'LL 3 c - o CD 3 ba .. + :;; ~ tcF711 ba ...

t~ .. ... n.1I ng 5 1 mm &ayer .

e- ~ 0 0.6 o 0.6 o c all8mallng 51 mm lay ...

0' a:s: 711 ''''1\110. and

OD_ lLs .D COl"" lite .. wDo l 01 oa: 711 II bergIaBa IW'II .D ..

CD (no. 3. 200 mkl roy lol m) medh.m 'Ine ateel wo 01 (no . O. 750 mica raylslm)

It

0.5 0.5

:: r: f- ·: - :: ... · ~""'''''29!"!'''r

12 In o 100 200 300 400 500 600 700 800 900 1000 o 100 200 300 400 500 600 700 800 900 1000 frequency. Hz frequency. Hz (c) Coarse steel wool in PLL.

(b) Single layer base and facings incorporated.

Figure 11. Performance of perpendicular layer lining.

basic wedge 0.9 0.8 'E~ CD CD

_ "

" c 0.7 E CD

!!l:g

".5 6lii 0.6

= ~

e-

o o c fII_ .c as 0.5 o 100 200 300 400 500 600 700 800 9001000 frequency, Hz (a) Acoustic performance in impedance tube. (b) Wedges used in coupon test in 40xBO test section.

Figure 12. Baseline OCF 703 fiberglass wedge with air gap. Resistivity: 27,000 mks ray/slm.

.... ... ; ·-·····~· · · · ···· ' ······· i!m5' · 0.9 _wedge only -o-config 2 ·· · ·· ·f··· ..... . ' ..... ... .. .

0.8 c_ ....

:gg ..

= .....

0.7 Olj

..·· ·· r·· .. ··· r···· .. ' .. · .. ···r ··· .. ··

u.5 c_ ~~

il l l

e.

o 0.6 o c .c

"'-

..

t····· ·· 0.5

TI II- ba.,ane 1

DO' 713 'Iborg_ -go t

FM125 a.,,,arld matal l

0.4;-~+-~+-~+-~~~~~~~~-+~-+~-+ o 100 200 300 400 500 600 700 800 900 1000 frequency. Hz (a) Technetics FM125 sintered-metal interface.

i i 0. 9 i 0 . 9 · .. 1- ... ..:... .. w ... ed .. g .. e ...o .. n.;Iy""ll' ... ·:. ...... ·" .. • .... • .......... :.. • ....... !:: .......

i ==: ~' - J.t;:E~ .

1 -o--conflg 5

0.8 0.8

.... ·I· .. · .... t ...... ·r .. ···r · .... · r~5" .. 1IIP

c_ ··1········!········!·······, .. ··· · / ..... .

....

II

:yg = ..

.....

...... J ... ..... L ....... L. ....... L.-- ... ~ ·.1 ~ == :: ..

0.7 = ..

.....

0.7 : : : :

.. ··· .. i ........ ·~· .... · .. ·r ...... ·r .... ·· ~:::.: .... .. 8:2

B~ c_ c_ o ..

: ! : :

o CD i ~ i i

:;:: I§ : : : : =I§ e.

..... .. i. ....... l .. -.-- -~.- .. ... .. ; ... .... . 7.0 .,.

o 0 .6 e.

o o c 0 .6 o c : ; : : 4.0 In

· .. ····f· ...... ·1 ·· ·· · .. ·i .. ······t .. · .. · :.i:::······

2l-

.. -

.c 7 7

.. [ ! ~ ~ , :31':31,,'7'21,':31,,71 1

CD ~ ~ ~ ~ : ::: ~ i .. !. !. !. :lonI1g5: ~ ....... ; ...... .. l ........ L ........ ~ ....... _ CCInIIg 12 : l .. lnl .. 0 .5 0.5 : : . : 42.0 In 1018' "liD" .

.......... :~ ........... !~ .•......• ~.:~ ...... ·• •• ,r· .. ·· ;:h7:!!~-::.:-p~; g • . r .. · ..

:: : ItbefOIIaa cloth Oop) :: ' bonded 10 pm p ... e + 111 In ho ... . 31 18 In as.gger) : , ; 1 a:F 703 Ilbergilla "edge 0 . 4;-~+-~+-~+-~~~~~~~~-t~-t~-r o 100 200 300 400 500 600 700 800 900 1000 o 100 200 300 400 500 600 700 800 900 1000 frequency. Hz frequency. Hz (c) 68%-open perforated 16 gauge plate with fiberglass (b) Perforated 12 gauge plate (40%-open area) with cloth on top.

cloth below plate.

Figure 13. Low-frequency sound absorption of OCF 713 fiberglass baseline wedge with various simulated lininglf/ow interfaces without grating.

~--wa"/ceiling-light --- panels 12 ga Sleel perforaled 'ace sheel 68% open perforalions 48" 3116" die holes on 7~ centlrs lOp view

=====6

stat 1298, 2" deep on 3" cenllrs, perforaled w11h 3116" 46 " holes on 1/ 4" centers (51% open) fiberglass filler media (Flbalr) between slats ,elalned by wl,e mesh ----------- Figure 14. Location of floor, wall, and ceiling ~~ed ~ ;; ; ;;;;;;;;;;;;;;;; ~ ;;~ (~~~:~n~~~S(~ flow/interface panels" The floor panels are designed to view 1 :!lP ':"" :: : '<: ;; ;:: ' !Wj llf · liIi;;'! ---perloraled&hael support personnel and equipment. The lower wall panels are to support personnel only.

3 . 75" deep oule, ',ame (b) Lower wall panel; two flat sections are used to approximate the local wall curvature.

-_...- __ - 12 ga aleel parfo,aled 'aca ohaal 88% opan perfo,allona 3/18· dla holao on 7/32" canlar8 48" lop vlaw

---.r----,6 ge alaal perforalad shaa •

."-~-~-~-:-:-:-:-=-==.",..,,,'=:.

68". open per1orationa

31 16" dla holaa on 7/32· canlera , lop 48" view alai: 12 ga, 2" deep on 1.38" canla,a, parfo,aled wl.h 3/18" 48" holaa on 1/4" can'a,a (51% opan) alai: 16 ga, 1.25" daap on 6 . 0· ------ cenle,. , parfore'"d with 3116"

"bergto .. ""a, media

------ 48" (AbaIr) between alalo hOi. a o.n 114" cenlaro (51% open) ,etalned by wl,e mesh n __ n __ n __ n_nn ___ E rf I d' h I 'Iberglua IIIle, media axp • .... ......... _________ ._ • . • ~ pe ora8 ace. 88 lod d ,.: (Flbal,) between ala.o alde I I I view / Italnl ••• ateel screen Dulch twill : 200 warp by 3 .75" daap oule, ',ame 800 shu'a wl,eann, axploded - - - - - - - - - - - - - - - - - - - - - - -0( otalnlo .. oleelo .... n on flow ald.

0 . 0024 .n by 0.0018 In da .

~: N ,:: , : :~;: ; :;q; ' ~ ~::a::c~::~n aollg. IS(e»

8 - 10 ego rayla al 100 em / l.c alropeed, dillualon bonded '0 perfora'ed 'ace ahaal 2 .0" oule, f,ama (a) Floor panel.

(c) Ceiling panel; upper wall panel is similar with kink in outer frame as shown in figure 15(b) Figure 15. Typical grating panel and porous face sheet.

' 1 .

o.g · · ~·· · ····· · 1 ·- · ···· · t ····· 6S ,. perforated pial e i : : ~2gauge) i : : ! : : .... : .. ~ ..... . ; ........ . .... .

0.8 l : 1.5 I nch deep 9rat Ing c~ 0.5 Inch air ~ ",G> 29 In ug cx:F703 !EG> 0.7 G>-O 8~ c_ Olli 71n

;:e

4+--n'~"""'''' 0.6 e- o ····· ··· ! ·· ···· .. ·! ·· .. ·· .. t ··· ..

°c

!l-

n"""

os ~

l l ~

Conng p2: ..... .. , ..... ... '[ ... . .... '1 . ... .

0 .5 42.0 In total height perforate + grating + Db erglass _dge 0 .4 100 200 300 400 500 600 700 800 900 1000 frequency , Hz (a) Floor grating with perforated sheet above.

. . . .

• . . , 88% 12 ga perl with .. ..: ........ ":' . ... -~ .. ~ .... .. .. ': 0.9 0.9 : : : : 0.8 0.8 .. ···1··· · ·· ·· ·1 ·· ··· ··+·_···· 1 ··· · ·· ·· 0.25 In aI. gap c~ : : :: batw-. tip and c ~ _ wedge only 28.25 backing

~g : ii i 40~ i :§ g

!E '" ",-0 ",-0 ....... -o-conflg 7

= '" 0.7

0 .7

.~: . . :: . ' I" ~ .... -

8~ B~ c_

-.--~~~ i c _

o III 7 .0 In

;:e .g§

e- e- o o 0.6 o c 0.6 .... · .. , ·· · .... · T·· · .... ·j'-·· _ .. ·[ 121n T .... ..

o c 10- .Q ~ - III : : : Conllg 6:

'"

1 1 1 cx:F 703 Ilberg lass wedge +

••••••• , .:r'.r.: .,~

....... i ...... . ) .. .... ... ; ......... i cloth + 1-1 / 2 In grating + ., ...... .

0.5 0 .5 ~ . : i 12 ga perforated plate ( 11 8 ~ , : holes on 3 / 16 ~ staggerIKI

: I ! I ~ :~"=.I>=: )

i i canters)

0 . 4 +-~+-~+-~~~~~~~~-4~-4~-+~-+ o 100 200 300 400 500 800 700 800 900 1000 o 100 200 300 400 500 600 700 800 900 1000 frequency, Hz frequency. Hz (c) Floor grating with stainless-steel screen below (b) Floor grating with cloth under grating.

perforated sheet (Rf = 25 cgs rayls for performance

plus screen).

Figure 16. Effect of floor flowllining interface on low-frequency sound absorption. Wedge-only configuration is with or without 4-in. air gap under base as illustrated.

I I _ wedge only I I I : -0- config pS I I I I

T --,- -- r- - T--'--

0.9 0.9 I I I I I I I I I I I I I 68910 perforated plate I I I

.. -1"--; - --1-- (12 gauge)

..

c_ c_ 0.8 0 .8 I I I CII .!!

u

: l1 g

I I I . !.!

c CII :t:CII I I I :t: 8:2 I I I 8:2 2 inch deep grating ug u g --1"--;---1- _. --+- - 4---1- - 0.7 lll,'rw--_OCF 703 0.7 c= filled with Scoth I I I 0", ~i : : : 29 in . ., E I I I "' E E!-~ I I I I I I E!-o I I I I I I 51 c on c __ .l __ ..J ___ L..._ .a- .a- -- + -- -+ -- -1 -_ .

0.6 0.6 co I I I I I I "' I I I I I I I I I I I I I I I Cbnfig pl : __ L _ L __ L ~'h-T7~'7 Config pS: -- +--4 ---4--· 0.5 042 .0 in total height 0.5 I I I I I I 42.0 in total height grating + fiberglass I I I - oriy ;. ocr 703 - perforate + grating ... dge I I I ... gop ,.;,,-, -,. fiberglass wedge I I I 0.4 ~~~~:'~~~~~~r---t-~+-~;-~-r~-r~-t~ -t

0.4 +-'"-4 ........ +-'--1---'--+'"""'---+---'-1- ......... +---+-+"'""""+

o 100 200 300 400 500 600 700 800 900 1000 o 100 200 300 400 500 600 700 800 900 1000 frequency, Hz frequency, Hz (a) Floor grating with fine steel wool between the slats.

(c) Floor grating with Scotch Brite between slats, perforated sheet above. Scotch Brite is a highly porous stiff nylon mat coated with abresive resin used as a scrub (no screen).

I I I I I I I I I I 0.9

--r--,---r--,---r-- --

0.9 "'" 12 go perl .. th I I I I I I .teeI saHn~ I I I I : L-"""T"--r--"T'""'" I I I ...

.. c_

0.8 0.8 c_ til til

-~--+ --~ ---~ l

I I I I old 1.5" tal _ "",'0 . !!! ~ I I I I +fI8AIR (36 gmtoq It) ~~ ~~ I I I 1 29 .5 In sliced .. '" ., .... 1. 5"

I I I I __ , _0<1 .. _

8:2 8:2 u g u g 0.7 0.7 c ·- -- r- - "- -"1 ---r """""" sting II-. l .7S" c ·- Oa; I I I I _'011-.1-3116 I I I I __ . g~ . ~~ I I I I 7.0 ..

~g filc I I I I OCF703 .g- .8-

0.6 --~---:-.--~--~-

0.6 - - r - - ,. - - "1 - - -r 4.0 "-r7'"T7-r7'"T"7 I I I I "' I I I I 7777171/ I I I I I I I I 7,n I I I I ~ I I , I I I I I. ..

I I I l Oon/ilia: ---+---1---+---1 - W-rr:""""!"7 eonllg p4: 0.5 -- 1" - - "-- "1- - - r 42 .0 In total hoigh' I I I I 0.5 42.0 In total heI ght I I I I Bonded 51 screen (ballorn) + I I I I perforate + grating +

I I I I wedge triy indudn I I := grate +lDt FI8AIR Ilnps compreaed

fiberglass wedge I I I I .. II'P I I 29'"::~· 7;3 N>etJjIoa wodga 0.4 o 100 200 300 400 500 600 700 800 900 1000 o 100 200 300 400 500 600 700 800 900 1000 frequency, Hz frequency, Hz (b) Floor grating with OCF 701 fiberglass between slats, (d) Floor grating with Fibair between slats, perforated perforated sheet above.

sheet with screen below (Rt = 25 cgs rayls for

perforation plus screen).

Figure 17. Effect of filler material between grates.

sound ~ source

~

0.9 ·········· ~ ·~· ·· ···r······i······!····· ~ ··· 1···· ~ ·············--··········· · ··+ · -·····-···· · ··

~ ! i ! i ! ! i i

c

.!!-m ~ : 1 ~ 1 j l ~ H_···· ···~······· run ... ~ ··-~·~··· l ····~· .. ! ..................... ...... .. { ..... ........... .

il g 0.8

~

: I : ~ 1 ~ ~ f ~-3 d1=10.9 « -<>-169AO : : : i : u~ c

: f ~ l l

-170AO .. .... ]" .. ·1 .. .. ;-- .. 1" .... · ................... T .......... .. ..

porous face

i ~ 0 .7

sheet

o 8

--17~BO ! ! ! i : 1l- III 0.6 .......... j ........ l .... ·T .... r .. r' j· .. t .... · ........ · .......... T ............ ..

0.5 3 4 5 6 7 8 910 20 1/3 ob center frequency, kHz (a) Panel and test rig not moved between runs.

OCF 703 fiberglass wedge anechoic tenmnation 3.Slnch air gap : : 0. 9 ···· ·· .. .. ~ ...... .. ·· .. ····· · · .... r .. ·· .... · ···· ' ...... ·· ········i .. ·· .. ·· .. ·· .. · ·· Figure 18. Wilby (ref. 15) test setup for two- microphone C ID~ measurement of high-frequency reflections from test :§ fl 0.8 .......... r ........ f .. · .... f ...... f .... ·f .... j .... f ............ · .... .. .. · .. · .... ··:· ··· ......... . .. .

== c samples. Specimen box and reference microphone are ID~ o ._ u ~ 48 in. into page, movable microphone is 24 in. into page.

-0- 199AO original Bet up

.§ i 0.7

~201AO panel Shifted 3.125 Inch

e.&

- 202AO panel shifted 5.75 inch is.

.......... _ ........ ·; ...... .. · .... '1" .. ··· .... .... 1 .......... · .................. .. .... .... ·· .. · .. .

III 0.6 0.5 , : : : incIdenllICCIUSIic pu'

0.4 ..... ·1-·· .. _· j .......... l .... · .. ·j .. 1 ......... , .... , .. ,-

0.5 ........ ; .... .. _-_.; ........ .• j ..•.•• uj _..... ~. ~ H ..... . r ....... . .... '" , ..

0.3 3 4 S 6 7 8 910 20 1/3 ob center frequency, kHz 0.2 ... .. ~ ! .. ...... L ........ i ...... L .... ... : '!~~~ .... ......

pulse !!! I

0.1

.. 11 .. · ...... (. ·T ........ ·: .... · ·· 1 ...... .. · ,"-' ... ... . .. ... "'1

(b) Effect of shifting panel In test rig (production panel > with screen).

ci '0 !l iii

-0.1 1 ...... ~ ..... ) ....... .. .... ....... . :::::::.~

a.

Figure 20. Data repeatability from three runs. Ceiling Ii -0.2 configuration: 16-ga, 680/0-open perforated plate :i:-'--· · : .~ . . . : ••••• . : ·. · · .· ••. ·.J without screen, 2-in. slats with Fibalr between slats.

-0.3 (Note: figs. a and b are different panels.)

-0.4 -0.5

·• ··.· •• 1 •• · . ··.11! .··r :, :":J

-0.6 '--~~ ____ .J....~...i....~....1.---'--'-~-1...~---L~--'~_ o 0.002 0.004 0.006 O.ooa 0.01 0.012 0.014 0:016 0.018 time. sec Figure 19. Typical chirp pulse and reflections. Time windows are applied to isolate the incident and reflected pulses.

40% open 16 gao perforated plate (0.12S"holes) backed by 38 mm deep slats on 32 mm centers 46% porous slats 2" heighi on 10. 7" spacing 0 .9 0.9 ··· ·· ·· · ··········r···················1··· · ··· ········· ·t·· ······ ·· ·· ··· · ·· · j·· ·· ··· ······ ··· ··· E II> E II> U ·u- :: :: fl ~ 0.8 ~ i 0.8 ······ ·· ·········· , · ·······[ · ·········· · ·· ·r··· ······· ...... , .. . .............. .

u u'C t:: c . ~ o 0- ::: .

: surface sheet ~ : ·j .... t .... .. · ...... ................ ·1 ........ ..

~ 0.7 e-:il 0 .7 0_ ···· .. ···· = · ~~~ ·· ~~~ ·· ~;~;~ · ~ .. ~~~~;~~ · ~~;~~~ ··· r ······ -- -- ... .... .

II> .c

- O· no interface . . , i

-o-FM 125 ~ -0- O· plate + slats ~ ~ : 0.6 .. -- .. . -'---~---------- .... . : -- ...... -- ...... --.

:: u.. = ~ O_ ! _ l! _ : __ _ ~'""'- .. · ....I · _ .. _ .. 1 '-. .. · ..... ·1 L.. .. _·_ .. ·_ · .. _ .. _ .. ·_ .. _ .. ·_ .. · _ .. _ .. ·_ .. _ .. · .... 1 .. _ .. _ .. ·.....J .. · 0.5 ~~~~~~~~~~~~~~~~ ~~~.....J 3 4 5 6 7 8 910 20 o 5 10 15 20 25 1/3 octave frequency. kHz 1/3 octave frequency. kHz Figure 21. Sound absorption of Wilby (ref. 18) pulse- Figure 23. Comparison of perforated plate/screen and reflection test device with and without a 40%-open FM 125 feltmeta/, both over a porous wall grating. The perforated plate over grating; acoustic incidence 16-gauge 68%-open perforated plate had a 200 by 200 angles from 0° to 45° in a plane perpendicular to the wires/inch screen on top. The FM125 was laid directly on grating slats. the wall grating.

0 .9 0.9 ·····- · ··· · E ···~······; · ······ +· · · · : . ..... t .... : : : .' . .. . ; : :: , ~ ..... ............... .... .

y E E II>

II> ~ ! i

u~ u~ - II> :; g 0.8

i gO.8

o ., u'C 8-8 cg c g 0- 0- ~ U, 0 .7

~~0.7 ~ I ~" ~ ::III.I

o~ 0_ -<>--680A. j i ~ i : 11 0>

.. _Technelics FM12S .a

--0-51% l 1 II !

0.6 • -a-Purolator 0.6 --33% .· .. ···· ·t .. ····l·--·· · :', .. t·· ·· t· ··· .... · ........ --·----··----··t ..... ... .

-+-Almute f 1 ~ , 1 l

0 .5 t..!:======t...J....l. ____ ..J..---I

0.5 '-----'-----'--~---'---'---'--'-------'---' 3 4 5 6 7 8 9 10 20 3 4 5 6 7 8 9 10 20 1/3 octave frequency. kHz 1/3 octave frequency. kHz Figure 22. Sound absorption of Wilby (ref. 18) test lining Figure 24. Effect of porosity on high-frequency (45°) with different porous metal surface coverings: absorption of a 0.0625-ln.-thlck (1.59 mm, 16 gal Technetics FM125 feltmetal (10 cgs rayls); Purolator perforated plate; hole diameter was 0.1875-in.

Poroplate, (10 cgs rayls); Almute (30 cgs rayls).

(4.76 mm). No support slats.

, ~ .. ',';' "" ,~~~.~~ • ••••••• • ' ••• ~~lw ••• •••••••• •• ••••• • •. - ; ';'" I • ~. " •••• ' . .. . • ... • » • -. • • • • • • • •••• • • •• • • • ., • . " .. ;.f. ~ ~ :t :.I ... • • ... • • • .. • • •• • ••• • • ••• tt • • • • • • • .....

. ·",.,:::::o·,,·: . ~ ... :::;.~:.,:::!:.~:: ... ::,: ::::":::: ::·

,. oj.I !>,~~"," ••• ".".1~~- ••• ( .• _.\'\.~t •• '''~···· · ·· ·''

WIJ./ ';. · ':":'':~'''' · ~ -'';':;;·~··:·':~''·;··· ''''·'fI:''· · :·· :··::; .. ; "'''7~':'. "." .... a.-fo.r-r·'··· , . .. ,~~~ •• " •••• t) •• " •• . 'J"~.' •••••• ~'.'" •• , •• ~~ ••• • • • •••• ' •• _ ... ,. ~ e -: • :It a • .- •• 4 ~ r'~ -, ..... ,>. ~ "_~~l" ,,:\ .•. , •• , •• , •• -, ., ..

-'~'l • .;.,"f:o- ••• y ... c.'i.tl;~"'~ ".~"'.'l.:,.tt',,~".'III.~ ••• 'Jlt

,'). 'l~!I r. fI" ....... ····:t,"'·· j ... ,:;.-; • .,.~,~ .... ,q ......... :': : <;':"Crri-,:,,,~':9'''~~''!''':'"!!'' "4t.~"·f'Jt_.···~····I."'1'1

,,':~';/;.: . .... t:,'/.~<:.'.:.:· :,: .;:.~·;·.:.:-:';:I·"·::~'O"~:::··:'

,., ','$>';<.' ,: \'(,~,,': ,'. t·· ';·:~\:.f;..'/'/'''.~'':''·::·

,')'1" ",=,,,;!...:~,}..,t"' '.!.~-,~*~ ... "''' •• ''.'''

'/:< :.,,\. .... ~/,n:-' • ,",:' .. '-':~i ;;~\'~f~~?,~:.::e·.::::'~'

• ,.":,;:,' .. ',' : . >;:( :\'.' /.~: .. " .. :.~::;.- ~ ~ ~ ;_, ' : ~.\ .~ ~., ~ _" • .." • to ... , ..

,"';"'; '~ •• "'.'''lIft ... ~ ,?"ft ..... ···: ::..,'~ .•. ., ...... f'.< t •• ; .. ~. , :. r. ; ,'. ~:~~.~';\,.,. •••••• 7.,"., ... ,.1 ..

.... : • ,~_~ .. \ ...... O( " ~ # ....... of - .

, __ •• 0., •• ' .

0 . 5 L---~--~--L-~~~~------ ----~~ 3 4 5 6 7 8 9 10 20 113 octave freouencv . kHz Figure 25. Photo of 68%-open perforated plate with 0.1875-in. (4.76 mm) diameter holes on 0.217 inch (5.51 (a) O.25-in.-thick plate.

mm) staggered centers; A36 steel sheet.

. .

. .

. . . .

0.9 · --·· .. ·· ···,· ........ ·' .. · .. --r .... j .. · .. r .. ·j· -- ; .. ·· ·· ·· ···· · ...... · .. · .. ,

! flow

E III 'u - ... .. .... .. j ........ .. L .. .... j ... .. . .; .. ... ~ .... J . .. J ..... .......... . ...... .

:: ~0.8 III C o III u't>

I ! I ~ ~ I I

'G 5.5 ~Ie dla. " porosity. --! ..... j .. .. ! .. . .. ........ . ... -------------- .. j -- ...... .

;: • 0 .7 e-~ 0_ Inch 0 __ . : : : : II

as __ 3116 51 j ! ! ! !

0.6

-0-1 /4 48 T ---- l .... ·[ .. ·r .... · .... · ...... · .. -- .. -- ...... ~ ...... ·-- ·

1 l 1 1 0 . 5 L---~--~--~~~~~----------~~ 5 6 7 8 9 10 20 3 4 113 octave frequency. kHz (b) O.0625-in.-thick plate.

Figure 27. Effect of hole diameter on sound absorption of porous plate; porosity held to 48% - 51 %, holes on staggered centers. No support slats.

d 0.189 L 0.2185 b 0.0295 X 0.187 P 67.9% dimensions in inches d and L are specified, b, X and P result

P = porosity

Figure 26. Uning-surface hole geometry for wall and ceiling perforated plate (12 and 16 gauge). (Nominal dimensions: geometry is distorted by punching process so that porosity can range from 65% to 68%.)

48% open perforated plate, 1/4 Inch hole diameter 114 inch hole diameter 0.9 0.9 C

c

.!

U

'" 'U- ~

. - QI QI 0.8 ........ .. . y . .. ... .

:; 8 O.B U o QI U"T) I!: '6 plate thickness, 15.s 0.7

!-

~~ 0.7 0 co

g!"2. =: ~ ~n~: .... t- ... ! .. ·r·r ·· · · .Q

QI ~ 0.6 0.6 ::~::6 ····· ·· I ······ 1· ·· ·· ·· ··· ··, .. · l' .. · ·· ·· ........ .. ··· .. · .. .... T .. · .... · 0.5 ~==:;::=:=t_L-Li.....J~ ____ -L~ 0.04 0 .08 0.12 0. 16 0.2 0.24 0.28 3 4 5 6 7 8 9 10 20 Perforated plate thickness, Inch 113 octave frequency, kHz (a) 48% porous sheet. Figure 29. Effect of acoustic incidence angle and plate thickness on sound absorption at 10kHz third octave band; no support slats.

3116 Inch hole diameter solid slat, slat spacing 1.19 Inch 0.9

rtf j m ~~

I., 0.9 ............ t ...... · T.... .

...... .... ·t ........ l .... .. r .. ·T .... t .. ·: .. ·l .... ...... ............ .... · .... r .... · ..

:; g O.B ............ , ....... - .; .... ... .;. ...... ; ..... ; .... ; .... ; ..... ········· .. ·· .. ···· ·· ···· ···i·· ······ ..

8 -8 ': : : : : i i ........ =~:::=?:Ul i .. ' . .. .. ..................... - I.

~~ ii i ! ! ! !

~ ~ 0.7 .. ... slat :helght,: InCh : ...... i .... ·+ .... l .... j .. .............................. ·i ........ ..

0.6 .. ·r·r · .. .. · ........ ............ ·r .... ..

~~ ~ ! ~ ~ 1 i !

~ -0-0 .5 :::: : : i 0.5 '--_--'-_---''---'-_..I....-~-'--'- ______ ~_.....J 3 4 5 6 7 8 9 10

0.' . =:=:: !I "' rtt

1/3 octave frequency, kHz 0.5 '----~--~--~--~~~~----------~-----' 3 4 5 6 7 8 910 20 1/3 octave frequency, kHz (b) 68% porous sheet.

Figure 28. Comparison of sound absorption coefficients for porous plates of different thicknesses; Figure 30. Effect of support grating slat height on sound no support slats.

absorption; sound ray in plane perpendicular to slats; no porous cover plate.

: :

0.9 ······· · _,···· .. ···r····· . ........ .......... ... .. 0 .9

· .......... ! .. · .... .. ~ .. · .... ·I· ·· · )" .. ·I· .. ·1 .... I .. · .. ·· · .. · .. ·· .... · .... -··· ··· ~ ··· .. · ··· C III

;g'B

0 .8 -c:: ·· .... · .... l .. .... ··r .. .. .. r .... T .. ·T····l .... j ........ · .. ·· .. ·· .. ·· .. ···· .. ·· [ ........ .

III III 8:e u islat porosity, 1 i j i ]:J:, rrl ' Ti c c:: 0- inch ~ ; ......... i ...... : ..... ~ .... i .......................... H ••••• j ........ . 0 . 7 .. · .... Effint · -j-- .. ·t .... ! .... I· .......... · .. · .. · .... · .... · .. --t- .. · .. · ..

j r--J..-,--"-1 !': 1: !

e.~ 0- -<>-9.5 i ::; : .c

'"

III ....... 8 .... I ...... 1 .... . ! .... J .... I .. .. .... . ................ . ... .. .1 ...... .. .

0 . 6 :::::~~5 .... .J ..... ~ .... .l. ... L.l ........ ......................... ~ ........ .

0 . 6 _1.188 : : ! ! 1 1

i I I i I : I I

: : : : 1 0 .5 0 .5 '--_-'-_-'-_-'---'-~-'---'- _____ ---'~--.J 3 4 5 6 7 8 9 10 20 3 4 5 6 7 8 9 10 113 octave frequency, kHz 113 octave frequency, kHz Figure 31. Effect of support grating slat spacing on Figure 33. Effect of grating slat porosity on sound sound absorption; no porous cover plate, solid slats absorption; no porous cover, slats 1 In. deep on 1 in. deep.

2.375 -In. spacing.

0.9 0.9 .. ...... .. T ...... r .... · .... ·t · .... ;· '1" .. 1" ............ . .......... r ...... -r ...... .;. .. · .. rr·r r ........ ........ · .... · ...... r .... ·_ ..

C C III .9!~ !: I:: : : 'OeD :: : : i ~ ~ : : . ! : : : : _u ....... ~ .. ~ .......... : .. - .... ~ ...... -:- ..... : . ... ~ .... ! ................................ ; ....... -- 0.8 Gl i 0.8 c:: ······· ·· ·· ·f····· .... ··r· ···· ··l······r· ·· ··f····r··· f" ·· ...... .. ... ...... . ....... ···T···· ····· Gi o III 8:e u:e u l ~ ~~~l l ~ u

C c:: g .5

: ~ : ! i ! ! : 0- . . . . . . . ...... .. .......... :. ........ .

~~~:~~ . · :ntt .. o .' "" """ " "" " "" "" """, :'

0.7

e. b 0.7

e.f; -<>-flberglass between slats

o~ 0- 1: .c -0- no fill between slats

'" . -0-- perpendicular

as L.-,-~-.,---,--;-~-,-- - -' ...... .... .... .... .. ....... ..

0.6 CD 0.6 '-----,---.,---~-'i ··· · · l .... r···]'························· ···· .. [ ........ .

l : i ~

0 .5 0.5 ~--~--~--~~~~-L----------~--~ 3 4 5 8 7 8 9 10 20 3 4 5 6 7 8 910 20 1/3 octave frequency, kHz 1/3 octave frequency, kHz (a) OCF 701 fiberglass filler, 3-in. deep, 12 gauge 68% Figure 32. Effect of grating orientation relative to plane porous performance plate, 63%-porous slats 3 in. height containing acoustic Incidence and reflected rays; no on 1.19 in. spacing porous cover plate, solid slats 1 in. deep on 1. 19-in.

centers.

Figure 34. Effect of bulk material between grating slats on sound absorption; screen on top of perforated plate.

12 ga 68% porous perf plate.

63% porous slats 2" height on 1 .19' spacing 5 r---------~------~------~------~ .. .... . ...... :, ...................... ~ ... . ............ ...... ~ .... .

~ 4 . --Real

~ 3

~CD .- u

] ~'m~I:~ iLt

u c 2 "i~ ::I U o c u .- III • o ~!!o iii E -1 ··t·········· . ..... .. .. .......... . ............ .. ....... .. .. . .... . ; ... . .. ... .. .. .. ..... 1" .. .

o c 0.5 -2 3 4 5 6 7 8 9 10 20 1.2 1cf 1.6 10' 2 10' 4000 8000 Frequency Hz 1/3 octsve frequency. kHz (b) Stainless steel wool filler (fine grade 0, O. 178 - (d) Impedance normalized by Pc, no fill between 0.241 mm wire diameter).

grating slats.

. .

... ... .... ........ . ... .. . .. . . ....... 1 .. ... ....... ~H •• ~ • • • •

0.9 'E ., u~ j ; - ..

= u ... j . . ..... . . . ... ... ... . ; . ... .............. '[ .. ....•. ... . . ... 1' . ................... , . .. .

0.8 ..

c ., u'C 'u C c 0- 0.7 ~o o~ on .<> III

I =~,,~=;:"· r l

0.8 0.5 L-L- ____ ~L- ____ ~L- ____ ~ ______ ~~ 4000 8000 1.2 10' 1.6 10' 2 10' 8000 1.2 1cf 1.6 10' 210' FREOJENCV. HZ Frequency Hz (c) Narrowband absorption coefficients.

e) Impedance normal/zed by Pc, steel wool between slats.

Figure 34. Concluded.

j 0 .9 ··· ··· ···· r ·· ······,······T -· r· · ... ~ ··7· ·

e i 0 .8 · · · · -····· i ~ ·. ···. · i .. .... .. ; . .. -. i .. .... t ..... l . ... . ~ .. - .. .. ... ..... . ...... ..

;1 I I I I I ; I

... .. .. .. ..... .. ........ ... ... ..........

~~ 0 .7 -no cloth o!2.

,g -o-drapedcloth ..

-0- cloth light gl ue 0 .6 .. ...... . .. .. .............. .. ~ :. : ." " """ __ cloth reticulated gl ue f : : 0.5 '--_....I-_-'-----'_-'--..J-.-'--.l...- _____ L----.J 3 4 5 6 7 8 9 10 20 1/3 octave frequency. kHz Figure 36. Deleterious effect of fiberglass cloth with adhesive below porous surface layer (12 gauge, 68%- open plate over 1-in. perforated slats at 9.5-in. spacing) (a) Floor grating (AC94-0071-736).

4 5 6 7 8 9 10 20 1/3 octave frequency. kHz (b) Wall grating (AC94-0071-734).

Figure 37. Effect of adhesive on sound absorption with Figure 35. Fibair lightweight fiberglass filter material 68%-open perforated plate and wire mesh screen glued placed between grating slats.

to the wedge side of a 12-gauge plate. Screen 200xBOO mesh, 0.061 mm and 0.046 mm dla warp and shute, twilled Dutch weave, 26 micron particle capture, 8-10 cgs rayls flow resistance.

12 ga 68% open perf plate on open frame, screen below

mi t --Mi ~ i

0.9 ... ... .. -.:n· _ .. ··· :· .. ····:· · ··· · : ··· ··i····~··-·:····· ~ , .. . .. -..- .. . .... .

C 1 1 1 ~ ~ ~ l ~

11>- - II> ~ flow re 'sistance ~ ~ ~ g 0.8

:e

II> II> ········ ·r ···· (scr::: r:yrserf: , T · r· ·· ·· · ·· · ··· .. ....... .. r- . .. . .... .

0:2 u u .5 c ......... ~ -0- 5 . 24 .. -+ ... ~ ... ~ .. ...... ...... .. ... ... .. ... + .. ............. .

0.7 ~~ e-~ o 0 .. c .c-

I =~ ~::~ i I I i

III 0.6

.......... : -28.76 "'r ' T'r ..... . . . .. . ... . .. ... .... r ·· ····· · ····· ···

0.5 3 4 5 6 7 8 910 20 113 ob center frequency, kHz (a) Magnified view of screen bonded to perforated plate. (a) 12-gauge 68%-perforated plate, screen below plate.

2' wall frame with Flbalr 0 .9 "E CD~ ._ CD o 0 - c::: 0.6

= CD

CD-c 0- o 0 c:::

T ~ g=

. .. -o--no screen 0.7 o. l108r -;: ~ - -0-·325)(325, 5.0 e-~ ___ 165x800', 10 . 44 ' o 0 C/) c::: _20Ox600, 15. 30 '

L ~==-= ~~ .a-

0.6 . .. -o-200x600, lii 15.65 ' __ 165x800, 29 .20 ' -L ~ , modified O. OO2Z· ';:::11r ~~ T~== 4 5 6 7 8 910 20 1/3 ob center frequency, kHz (b) 16-gauge 68%-perforated plate (screen above plate).

(b) Screen weave size.

Figure 38. Stainless-steel screen geometry. Figure 39. Sound absorption of diffusion bonded plate/ screen over lining with various values of flow resistance created by variations in screen mesh geometry.

16 ga 68% open perf plate with screen above, 2" wall frame + Abair 2' perf slats at 12 '

tn·, :$:t4 I

0.9 0.9

c

c ... .... . .. :. _j_ .. ·r ·· ·'·· ·!IT i

.. ~

mi++ ~

- .. .!m-

u u ,gg Rf, cga rayls i : i ; :: i - ., "'0 :8:2 ....... (~~~~~~ ., ~ . f .. . ~~ .~ . ~I · ~ · ····i· ··· ;· · ··~ ··· ··· ....................... . j ... ... ...... ... ..

8 gO.8 ···· ········ ··········· ··· ·· · ·· .·····:····c····.·· ·· · ......................... -; .... .. ...........

u g 0.8 c: .- §~

::::~~:~ I ii j

- E ~:~:~ :~: ; ; . I : --0-21.2 ; ; ; ;

i1

~o . ....... .. ; . ....... . ~ .. ..... i· ····· ~ . .... ~ .... ~ . ... ~ . ..... .. . ... , ,- ........ .... ... ~ ....... ,- -. .... .

~ .:0.7

~ oS 0.7

~!H I !! -!rm__--r-

: 1 I : I : : 0.6 0.6 L---~--~~~~~~ -------- ~----~ 3 4 5 6 7 8 910 20 3 4 5 6 7 6 910 20 1/3 ob center frequency, kHz 113 ob center frequency, kHz (a) a versus frequency. Figure 41. Effect of screen position on performance of 12-gauge floor panel, 68% open; 2 in. perforated slats, 12 in.-stat spacing, no Fibair, 18 cgs rayls.

16 ga 68 % open perf plate with screen above, 2" wall frame + Flbalr . . . .

~ : : ~ :

...... £2 . 1... ... ..... ...... ..J. ..... 25?~ . ~ :!

0.9 0.9 * : : : - ~ .......... ~

c

., ~

: : : : ~ l

l

.- ., .2 g frequ~ncy : : :

rl -l i l- 4

i~ .-_---::kH;.,;,z::..,. .. ....... . .... L .......... . .... .. l. ... ......... ...... L ........... .. .... .

. .. . ..... . 1.. _____ .. . ... . ... : .. .... : .. ... i . ~ .. i .. - .i ................ .. ........... ~ ............... _ 8'g 0.8 __ 4 : : i c: .-

~~

=::::~ ~bo: II ! 1

(; g ::::.3 .............. l. .... ............. .1.. ............... ..1. ..... ........... ..

i - 0.7

r-'- -" [ Ir----r

~~:~ · ~ i ~ i ~· 5 ~~~-1 : ~~~~I~~~~L · i~ __ ~~

l

0.6 0.6 16 18 20 22 24 26 3 4 5 6 7 8 910 20 Flow resistance, cga rayls 113 ob center frequency, kHz (b) a versus flow resistance (cross-plot of (a)).

Figure 42. Effect of screen position on performance of 16-gauge 68%-open wall panel; 2-in. perforated slats, Figure 40. Sound absorption of diffusion-bonded 12-in. slat spacing, no Fibair, 15.85 cgs rayls.

plate/screen over lining with various values of flow resistance. The screen mesh was common for all curves.

Screen above perforated plate.

0.9 ..

c~ I . 91 0> I g

:e

I I 8~ I I I 0.8

--,--1'

-------,----

g~ ._ ca I I I I I I

"e e-

o I I I 5l c I I I .D - ca

0.7 ---j--1'-_I

I I I I I I I I I I I I 0.6 1...-_-'---_'---'---'---'--'--'- ____ ----'- __ --' 3 4 5 6 7 8 9 10 20 1/3 ob center frequency, kHz (a) Dirty production panel before and after cleaning.

(a) Grating and porous cover removed.

1. 22 m by 1. 22 m 0 .5 m wid. gird., liang. 0 .6 m by 1. 22 m 0Jd1llng lining 16 ga 68% open perf plate with screen, modul.8 pia.... undor 76 mm flbarg.... module 2 place. 152 mm dHP 2" wall frame slats I I

--"--T- .,-.,-r l

plan vI_ I I I I I I I 0.8

--.,--T-.,-.,-T, -r---- ---.,----

I I I I I I I I ..

c~ --,--1'-,-,-~4-r-------,---- .!! Q) I I I I I I I I

E ~ 0.6

--,--1'-,--j-~4-r-------,---- :!l:2 I I I I I I I I ~ . ~ --~q.~ti-r-~---~--- ,2 "iii

.. e 0.4

-- -t-i-1-ri-j-------i----

e- o 51 c .t2~ ---j--+-_I--t-+~-r-------_I---- I

"'

flow -0- original panel, 1 5.3 cgs rayls -4---- 0.2 • levatlon floor

_ very dirty panel •

I ~ cleaned with acetone and shop air -4---- I o~--~--~~~~~~~----------~----~ 3 4 5 6 7 8 9 10 20 1/3 ob center frequency, kHz fibergla •• wedge. I., •• mwl •• grating with poroua .ace ahe •• above (b) Panel contaminated with jet fuel smoke and subsequently cleaned. (b) Geometry.

Figure 44. Coupon modules mounted in 40xBO test Figure 43. Effect on sound absorption of section floor for aerodynamic and acoustic testing.

cleaning panels.

Figure 45. Coupon test rig setup for static sound absorption. Four loudspeakers are mounted on arc over test module. Fiberglass blanket was used to shield hard points outside test area.

12 ga 68% porous perl plale, 63% porous slals 2" helg.

16 ga 68% porous perl plale on 1.188" spacing 1 r--- ~~~~~~~~ ------ --~-- --~

~ ) l j

··········i······ .. ·t···· ·· t· · · · · 1 ···· ·~ · ·· · i ··· · t · ···· . .. .. ....... . ..... ... .. . ; ... .... .. . __ ... .

0.9

··········,········"( · ·····i····· .... ··r··!

i-

~ ~ l l ~ l i j

o~ !f IS .... ...... ~ ........ . ~ ....... ~ . .... 1 .. ... ~ .. .. 1 . .. . ~ ... - ... - ..... ,- ... .... ....... ~ ... ..... .- ..... .

0.8 ~:2 ~ i i 1 ~ 1 1 1 o g c- ::::::::::-::::::::[::1'::1:: '1': :1:::[···· · ··· · ·········-:::::::::1::::.:: : :::::::: Oiij . ....... ..I. .... ... l .... .. ~ .. ... L..I 1... .1.. ..... ... ...... . .. . ... .. .. .. 1.. ......... .. .. .

0.7

:;:: E

-<>-Iab rig (no sial fiberglass) ~o ~ lab rig (no slals) o c -0- floor coupon (OC 701 fiberglass Il- -o-wall coupon wllh 1 Inch slals and OC 701 between slals) III 0.6 fiberglass between slals 0.5 L-_ -'---- --' _ -'- --'----'-- -'---'- ______ --'-- _ _ -' O.5 L--~~--'----~~~~----~--~ 3 45678910 20 3 4 5 6 7 8 910 20 1/3 oclave frequency, kHz 1/3 oclave frequency, kHz (a) Floor configuration (the lab rig sample had no (b) Wall configuration (lab rig sample contained no slats).

fiberglass between the slats).

Figure 46. A comparison of 40xBO coupon and laboratory test rig results. The OC 701 fiberglass between the slats was detrimental to sound absorption at high frequencies.

20 ga 62% porous perf plate, 51% porous slats 1" helg on 6" spacing, OC 701 fiberglass between slats 12 ga 68% porous perf plate

1 r-~~~~~--~--1

0 .9 . 1 : E 0.9 CD~ ····· ···· t·· ·_· r " ' r"'~" . ... ' ..

C u !'.l CD~ _CD U u 0.8 == Iii c :: ~:2 0.8 CD CD u g ····· 1 ,·····1··[111········ · . .. .... ....... .

0:2

!j t lf lr

c .- u~ .2 iii 0.7 .§iiI 0.7

- E . ... .. _ . t·· ··· ·, t· · h" ~_ - •• -t o .. ' l'· · · ~ · · '1 '········ ··· ····

==:::: :~~~~ ~~~ ~:::~ ... . ........... !""" .. ..... .. . .. ..

e-

- E

o e-

o c o o c Il-

~-

76 mm below surface ea 0.6 ·· ··· · ·· ·····r ·········· · ···· 0.6

J .. ~ l t J IF " " " J . . . ,, '

0.5 L---~--~~~~~~----------~----~ 0.5 3 4 5 6 7 8 910 20 3 4 5 6 7 8 910 20 113 octave frequency, kHz 113 octave frequency, kHz (a) 12 gauge, 68%-open perforated plate above an Figure 47. 40x80 wall coupon with and without a ring anechoic termination.

girder 6 in. (152 mm) below the flow surface. Ring girder was covered by OCF 701 fiberglass.

16 ga 68% porous perl plate ~ WIlby & WIlby : data [15) ........... ~ . Mechel & Ver [6) 0.9

. · ······ · (···· .. ·T .... · ~ ·- ·· r·· ·r· ··j-· · t .... '·

: model 1 ~- 39.5 ft - ..

: mod812 .2 g

iii i :Ingald 125

.. I ......... : ........ : .... .. : .... ! .... ..:- . .. ; ... ; .......................

:; .. 0.8 8~ 1 1 ! ~ j j 1 c

a=

;: ~ 0.7

e-

o ~s III 0.6

lli[Itll

~ j 1 ~ ~ ~ 1 0.5 ~ __ .i..- ~ __ .L-~~i......L ________ --' ____ ---1 3 45678910 20 1/3 oclave frequency, kHz (b) 16 gauge, 68%-open perforated plate over an anechoic termination.

Figure 49 . Comparison of predicted and measured high- frequency sound absorption. Four analytical models are plotted along with pulse-reflection data from Wilby and Wi/by (ref. 18).

tum table: 35.3 ft diameter Figure 48. Plan of test section tumtable showing depths (inches) of special lining modules in that area. Outside this area, the lining depth is generally 42 in.

diffuser column wrtex generator on CL (8 total) 11.4 ft chord

O

--.........,,......---- 2S in thick 46 i nChhi9h.

4S ft 1 S ft from centerline

q{

j b diffuser ramp

4.S !--------.,o( (steel sheet) 6ft 6 inch deep diffuser 20 ft lining in 4 ft squares formed by metal struts turntable lining efeva.lon View nClloscaJe 83 ft deep lining deep Ining In lest &eQi cn inlet ramp (steel sheet) bulk flborgiaOG 1 I bo. It OCf 701 III cloth bag 12 ft fJ.P Steven. f 675) . 12 g. _ 1 ..,!Ioa oaO«l boiow

16 ga . st. on walls and ceiJing . SCtMfl on now side

(b) Elevation.

(a) Plan view of floor.

Figure 50. The shallow lining in the diffuser inlet.

ll2"xl"lc19ga.

top lAew with Interface panel removed wedge galvanized wire

I LOWER WALL I

3/1 6" dla holes meSh wedge tiP valley on 7/32" centers ..-: plan lliew ~:l flber9ass doth ~ 5.5 oZIVct2 10 cgs

\

ralAs . JP Stevens 16"75 3 to 3.25 Ibllt fibefQiaSS OCF"703 or eqJ al 65 cgs ra)ls/lnch

- - -

at 100 an / sec elevation .

-ill elevanon view • n ow interface panel P""1IIIIIl=1IDI!"I"""Pcn:'F~ ;'~ wi th !rating .

etc.

-

1/4"Up gap ~..L.s.:.--H--r/7 wedge.

3.75 in wedge peak pressure Sh e! .

/" .

outer 12 ga perforated frame base slats on 3" air gap L...- _____ ---'c......I centers (311 6" holes on base aw gap .

114" centers, 51')6 open) ~ ~75 (c) Lower waJl panel.

(a) Wedge detail.

I UPPER WALUCEIUNG I

3/16 " I1 la holes on 7/ 32 " centers plan lliew plan vi ew (all locatio n51 -- - - " • ~ ••• I ~ I ~ • n , •••• " • " I ••• • ••• ' I •••• ~ ..... " I •• , I •• 0 • • ••••••• I I •• R •••• I • I ~ I • I " .. ... ... ~ .... ~. " ... ..... .. , •••••• ,"'- •••• ,., •• 0 •••• ........................ , , • •••••• c,<. I I ••••• I • ••

.:.::~,:: .. 'h • ••• ".H ••••••••••• 0 • •••••

etc.

•..... . . -.

• • ••• ~ I " • " •• ". • •• , ••• : I ,

-

, ..................... " ..

• • • I , • ~ • ~ •• I • _. • ••• :. I ••

• ••

. ..... ...... "" .. " ........ '

etc.

- - - , elevation above 68% open elevation 1-1/4 in 16 ga perforated plate [ ~ 'Q ~~ etc.

r,~m~ ~ ~Jilli.~~~.ID Z: T -

outer 1 6 ga perforated frame slats on 6" centers (3/16" holes on centers 1/4" centers ( 3/ 16" r,oles on 5191t0pen) 1/4" centers, 51 <J1; ope n) tip (d) Upper wall/ceiling panel.

(b) Floor panel.

Figure 51. Final design geometry and specifications.

\

I

I

I

I

i

I

Form Approved

REPORT DOCUMENTATION PAGE

OMS No. 0704-0188 Public reportlng burden for this collectJon of Information Is estimated to average 1 hour per response. Including the time for reviewing Instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect 01 this collection 01 Information, Including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson DaviS Highway, Suhe 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget. Paperwork Reduction Project (0704·0188), Washington, DC 20503.

1. AGENCY USE ONLY (L.a". blank) 1 3. REPORT TYPE AND DATES COVERED 1 2. REPORT DATE Technical Publication November 2002 4, TITLE AND SUBTITLE 5. FUNDING NUMBERS Design and Development of a Deep Acoustic Lining for the 40- by SO-Foot Wind Tunnel Test Section , 519-20-32 6. AUTHOR(S) Paul T. Soderman, Fredric H. Schmitz, * Christopher S. Allen, Stephen M. Jaeger, ** Joe N. Sacco, Marianne Mosher, and Julie A. Hayest 8. PERFORMING ORGANIZATION 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) REPORT NUMBER Ames Research Center, Moffett Field, CA 94035-1000; *University of Maryland, College Park, MD 20742; **AerospaceComputing, Inc., at A-020S163 Ames Research Center, Moffett Field, CA 94035-1000; and tSignalscape, Inc., Raleigh, NC 27606 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER National Aeronautics and Space Administration NASAffP-2002-211S50 Washington, DC 20546-0001 11. SUPPLEMENTARY NOTES Point of Contact: Paul T. Soderman, Ames Research Center, MS 247-2, Moffett Field, CA 94035-1000 (650) 604-6675 128. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Unclassified - Unlimited Subject Category 09 Distribution: Standard Availability: NASA CASI (301) 621-0390 13. ABSTRACT (Max/mum 200 words) The work described in this report has made effective use of design teams to build a state-of-the-art anechoic wind-tunnel facility. Many potential design solutions were evaluated using engineering analysis, and computational tools. Design alternatives were then evaluated using specially developed testing tech- niques, Large-scale coupon testing was then performed to develop confidence that the preferred design would meet the acoustic, aerodynamic, and structural objectives of the project. Finally, designs were frozen and the final product was installed in the wind tunnel.

The result of this technically ambitious project has been the creation of a unique acoustic wind tunnel. Its large test section (39 ft x 79 ft x SO ft), potentially near-anechoic environment, and medium subsonic speed capability (M = 0.45) will support a full range of aeroacoustic testing-from rotorcraft and other vertical takeoff and landing aircraft to the takeoffflanding configurations of both subsonic and supersonic transports.

14. SUBJECT TERMS 15. NUMBER OF P~GES Aeroacoustics, Wind tunnel acoustics, Duct lining 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified NSN 7540-01-280-5500 Standard Form 298 (Rev . 2-89) p,.ac:rt_ by ANSI Sid . Z311-18 ~QA . .. n,