A two-dimensional laminar flow airfoil (NLF-0414) was subjected to high-intensity sound (pure tones and white noise) over a frequency range of 2 to 5 kHz, while immersed in a flow of 240 ft/sec (Rn of 3 million) in a quiet flow facility. Using a wake-rake, wake dynamic pressures were determined and the deficit in momentum was used to calculate a two dimensional drag coefficient. Significant increases in drag were observed when the airfoil was subjected to the high intensity sound at critical sound frequencies. However, the increased drag was not accompanied by movement of the transition location

Baals, Robert A.

Jones, Michael G.

Shearin, John G.

English

NASA Technical Reports Server

NASA Technical Memorandum 100505 
ACOUSTIC EFFECTS O N  
PROFILE DRAG OF A 
LAMINAR FLOW AIRFOIL 
JOHN G. SHEARIN 
MICHAEL G. JONES 
ROBERT A. BAALS 
[NASA -TH - 10 05 0 5 )  ACOUSTIC EFFECTS ON 
PROFILE URBG OF A L A H I E J A R  FLOW A I R F O I L  
(NASA) 18 p A v a i l :  NTIS HC A02/HF A01 
N87-30155 
CSCL 20A U n c l a s  
63/7 1 @ IO2690 
SEPTEMBER 1987 
National Aeronautics and 
Space Administration 
Langley Research Center 
Hampton. Virginia 23665-5225 
https://ntrs.nasa.gov/search.jsp?R=19870020722 2020-03-20T08:48:57+00:00Z
John G .  Sliearin, Langley Research Center, Hanipton, Virginia 
Michael (4. Jones, PRC Kentrori, IIIC., Hanipton, Virginia 
Robert A.  Baals, Langley Research Center, Hampton, Virginia 
SUMMARY 
A two-climensional riatsural Ianiinar flow airfoil (NLF-0414) w a h  sii1)jected t o  high- 
intensity souiid (piire tones and white noise) over a freqiiency range of 2 t o  5 kHz,  while 
eiiiersed in a flow of 240 ft/sec (Rn nf  3 inillion) in a quiet flow facility. 1Tsillg a wake- 
rake, wake dynaiiiic pressures were deteriiiiiied and the deficit in inoiiirvitiiiii was used to 
calculate a two-cliiiiensional drag  coefficient. Siqiiificants increases in ClrijR w-re  olxwrved 
when t lie airfoil was  subjected t o  the high intensity sonnd a t  critical s o i i i i ( 1  t’rcclwiicies. 
However, the increased drag was not accompanied by iiioveiiieiit of the transition location. 
INTRODUCTION 
It is well known that the t,ransit.ion beliavior on laiiiiiiar flow airfnils is sensitive t.o 
free~t~reaiii tlist,urhance spectra. The dist,urbances can be in the forti1 o f  t,url)ulence fluc- 
t.u a.t.ions ( veloci t.y tlist,urbances) or acoustic fluc t.ua.t.ians ( pressure dist.it r1 )a.iices). Tliese 
freest. rean7 di s 1.11 rhaiices can a.ffec t, bo t.11 1.11~ 1oca.t.ion a.11 tl 111 ode ( i . t’ . doi i i i ii  a.11 t iris t. a.bil i t, y ) 
of t,he t ra.nsit.ioii process. 111 bhe t,wo-rliiiieiisioiia.1 flows, on a.ii iiiiswept. airfoil for example, 
t,hree of t.lie uiodes of t.raiisitioii which are of interest, iricliide la.iiiitia.r-se~~ara t ion-inrliictd 
iiist.al,ilit,y, viscous (‘~olliiiien-Sclilicli t.ing) iiist,dili t.y, atid roughness-intliict.cl i iistabili t.y. In 
t.he past,, ext,eiisive research has been condtict.ed on t.he effect.s of a.coiist.ic rlist urhamces 011 
laiiiina r scpa.ra.t.ic ) I I  beha.vior, and 011 Tolliiiieii-Scliliclit,iii~ a.iiiplifica?.t.ic,n a i i t l  rcla tcv l  t.raiisi- 
t . i o t i  locat ioiis. Ilowevcr, very 1it.t.lc iiiforinitt.ioii exist.s coircerniiiy; f,he i t i f l i i v i i w  of a.coust,ic 
clist.iirl,ances o i l  airfoil drag with t.ra.iisit,ion artificially intlured by  rony;lilic.ss. This report. 
1jresent.s t lie resri1t.s of a.ii experinient,al iiivest.igat,ioii 0 1 1  the efl’ect.s o f  acorrst ic r l i s t .u rh ices  
oil t.lie drag of it. laminar airfoil wit,h laiiiiiiar separat.ioii and  witch roiigh ness-iiitlucetl t.raii- 
sition. 
1 
SYMBOLS 
c airfoil chord, 24 inches 
C d  section profile-drag coefficient, . \ [(qtt t /qfs - ( q 7 , v / q f s  ) ] A h  
c /  section-lift coefficient. 
h 
!l dynamic pressure, lb/ft2 
Rn 
X airfoil ahscissa, inches 
z airfoil ordinate, inches 
vertical distance in wake profile, inches 
Reynolds number, based on free-stream conditions and airfoil chord 
Subscripts: 
f free-stream 
1 u  wake 
Abbreviations: 
dR decibels 
QFF 
N L F  N a t  tiral Laminar Flow 
OASPL Overall sound pressure level, dB 
SPL Sound Pressure Level, dB 
Quiet Flow Facility in the LaRC! Aircraft Noise Reduction Lalmratory 
DESCRIPTION OF AIRFOIL AND EXPERIMENTAL METHOD 
Air foil 
A sketch of talle section shape for tlie 14%-thick NLF (natural laminar flow) iiioclel 
airfoil is shown 011 figure 1. The inoclel was construct.ec1 of a rigid polyurethane foam 
and covered with fiberglass and a polyester resin. It, had chord and spii~i cliiiietisions of 
2.2 and 12 inches, respectively, and was sanded in tlie chordwise direction to assure a 
smooth aerodynaiiiic finish. It, was then painted flat black to aid in flow visiialization. A 
calculated pressure dist rihution for tlie test conditions is shown on figare 2. Aerodyiiaiiiic 
characterist,ics of the airfoil over a Mach nuinher range from 0.05 to 0.40 a.nd a Rn range 
from 3 million to 22 inillion are found in reference 1. 
d 
2 
Test Setup 
V 
A wake rake was centered (3 inches clownstream of  the airfoil trailing erlgc (figure 3). 
?'lie apparatus cmisistd of two standard static prolws and twrnty-sevf.li t o t a l  1)ressiire 
prohes, 0.1 25 inches in cliametcr. Wake-rake pressiire iiieasiireiiients were macle using 
variable-capacit ance precision transdiicers, which were connected to an aiitoinatic pressure- 
scanning system that recorded the to ta l  wake pressiires (averaged over 5 seconds) and 
related facility pressurcs. 1 hese mcasured pressiircs were iiscrl t o  calciilate t hc sectional 
d r a g  cocficierit. Figure 4 sliows t.lie c-alculatecl drag coniparetl with  drag flat it t akeii from 
reference 1. 
r i  
l'he airfoil was positioned over the jet nozzle sucli that the entire airfoil vhord was  iu 
t h e  potential core of tlie jet.. Rasetl oil previous hot-wire s ~ ~ r v e y s ,  thc jet was known to 
have utiiforiii iiieati flow arid a ttirljiilence level o f  apprc)ximately 0.005. 
In this st.ncly 1)ot  11 the riiicroplioiie a i i d  the iioihe soiirce \c-erc> in a {ixecl position. The 
~ ~ o i s e  o i ~ r c e  was iioriiial to aiic1 15 iticlirs froni  t lie airfoil cltorrl, aiid w a s  visitally clirectetl 
3 
RESULTS AND DISCUSSION 
Preseiit*ed and discussed iii this section are the efiects of an acoustic ~ m r c e  cni the  
profile-drag o f  it t w o  diiiieiisioiial airfoil. All (lata were taken at a Reynolds iiuiiil~er o f  
3 million and a M a c h  nniiiber of 0.22. The acnustic sources were p i r e  totic-s arid white 
noise. 
Airfoil Aerodynamic Definition 
‘The darkr~nccl synilmls on fignre 4 represent thc mcasrirerl R C ~ O ~ Y I I R I I I ~ C  cli;\racteristics 
of the  sir1,jec.t airioil, while tlie open synil~ols arc data  taken froin refrrcvicc. I .  A t  a Hi1 
o f  3 niillioii a laminar separation bubl>le shoultl occur at 74%) cliord (refcreiice 1 ). This 
biiI>ble was o1)servetl for tlie subject. airfoil by using liqiiitl Crystals. To ensure t raiisit.ion, 
sniootli surface tape (0.1 iiiclies wide ant1 .024 iiiclies thick)) was p l a d  a t  68% cliord. 
The difference i l l  the iiioclel drag tlat,a aiid the rderence t1at.a is attxil>uletl t o  {rip clrag. 
111 general, the tlat a in figure 4 iiitlicat,e that the niodel airfoil was j>erfnrini~ig its tlesigiiecl 
itiicl the wake rake iiieasurenieiif s were sufficiently accurate. 
Free Transition 
Figure 5 shows the effect of pure tones on the smooth airfoil (laininar I i i i l~b le  prw.eiit ). 
For tlie two soiiiid levels shown, t.he clrag increases as freq~tency increa.sr.s fro111 1.X kIiz  t n  
approximately 3 kHz. ’rllis drag in(-rease may result from t lie formard i i iot wilelit of the 
acoustically excited laiiiiriar hubhie, thus,  changing tlie ti irbnlti it  reat t acliiiiciit location. 
For frequencies a h v e  3 kHz the drag cliaiige is erratic a t  an SE’I, of  1:SO (113, Init increases 
cotisisteiitlg for  the case  of 138 dB. This latter drag increase will be cliscussed in a later 
sect ion of t l i i h  paper. 
4 
Fixed Transition 
T h e  theory o f  st,a.bilit,y of 1a.mina.r flow assumes that. the  iiieaii flow iit  t l i t -  cliortlwise 
dircct.ion is influeiicecl hy a tiuiiiber of discrete Ixdial fluct.uat,ing tlist,urhanccs. Furt.lier- 
more, these flucbuat8ions consist, of waves propagat,ec\ in t.he cliordwise dii.ect.ion. Each wa.ve 
1engt.h lias ail a.niplificat*ion factm t.liat. det,eniiines if the 1aaniiia.r ii1ea.n flow is st.a.l>le o r  UII- 
st,ahle. If the Ilow is iiiistsable and the dist,urhance wave is a.inplifim1, t.lic i raiisit io i i  loc a. t.' i o n  
will clia.nge aid increase tohe leiigt-li of  the  turbulent. region. However, t.lie Keynolcls iiiiiiiher 
inlist. he sufficieiii.ly large for t.he flow t.o he uiis tdde a.nd the dist.iirI)ances ani plifiecl. 
Wit11 traitsit ion fixed by rougliiiess, i i o  furflier tmnsition iiioveiiic-iit ~ i i s  observed 
(with liquid crystals)  i n  response t.o ai1 acoustic disturlmice. Ileiic-e. cxcit a t  ion of tlie 
natural  iiisialility waves leading t o  premature transition is iiot Iwlieved t o  I ) ( *  ! l i t*  priiiiary 
caiisc o f  the clrafi rise. The iiicreasr in drag is the effect o f  the s o u n d  exciting tlie flow 
near t he  airfoil hiirface (shear layer), t hus causing the existing turl)iilenct. i o  liecoiiie inc~re 
intense, possess a higher inixiiig rate ( ~ n o ~ n e n t u m ) ,  and illcrease the  skin friction. The 
sound inap have  also affected the rougliiiess ( t r ip  t ape )  drag. 
T h e  airfoil was made fiilly turbulent ( t r ipped at 5%) chord)  and sul)jected t o  a pure 
tone wiih a sound pressure level of J3X dB over a frequency range sliowii oii figure 9. This  
resulted in a drag  rise similar t o  that experienced by tlie laiiiinar airfoil showii o n  figure 6. 
This observat ion supports the conclusion that  the drag increase is dut. t o  i i t t  increase iii 
t 
CONCLUSIONS 
High-quality repeat able two-diniensional drag data  have he11 nieasiiretl o i l  a laminar  
and fully tnrl>iileiit (NLF-0414) airfoil while being sulijectcd t o  sounrl. Significant increases 
iii drag were ol,served when the  s o ~ n d  was of sufficient iiitciisity ovt’r it l i i i i i icr l  range of 
souiicl frec l~et~( . ies  (tilore tlian 40% drag increase for 138 (lF3). The iiit.rt*its(’ in clr;tg was 
olxerverl to lw linear w i t h  SPL in nature  and may h a w  Iw(~ii  tlic rwiili of‘ intciisifying 
the existing tiiri)uleiic.r~ near the airfoil surface, thlis increasing t l l v  skin fric-t i o i i  ilii(l/(jr 
roughness drag o f  the t r ip  tape. 
The restilt s indicate that in the iise of a laiiiinar airfoil one iiirist Iw ~-oiice~rned with 
increasing t l i e  t iirbiileiice iiiteiisity witli soiiiid, as well as affect.iiig t lie i l i i t  Ilritl i n h i  abilities 
of t h e  flow. Furthemiore, the additional drag resulting froni acoiistic (list iirlxiiices o i l  fully 
t iirbuleii t surfaces sliorild Le considered i n  all aerodynamic nieasnrenicnt h. 
Additional tirag data need t o  be acquired iisiiig a force halance and a sk i t i  f‘rictioii gage 
t o  corroborate the results prrsentecl herein. hsleasurenients o f  fluct iiat iiig \iirfi\ce stresses 
using hot-filni wisors should help t o  Iwt ter understand the physical p I i c i i o i i i ~ - i i a .  
R.E FE RE N C! E S 
I . M c.( II(Y., l{oIwid .I  .; Vi k c w  , .Ic.lltc*y K .; I’lvti tiiiiKvr, W t w i t b r ;  l h - ; i ~ l ( * y , \ V i l  Iia I 1 1  I ).; i l  l i t 1  
Harvey,Williaiii D.: Exyeriiiiental Results For A Flappecl Natiit-al-I,atiiitiat-I~’l~w hir- 
foil  With High I,ift./L)rag Ratio. NASA TM-85788, May? 1984. 
2. Holiiies, Bruce J .  and Olmra, Clifford .I.: Advances in Flow Visiialixation ITsiiig Liquid- 
Crystal Coatings. SAE Paper N o .  871017, April, 1987. 
c 
I 
0 
L 
0 F 
0 
N 
\ 
r . 
0 
T- . 
I 
c 
0 
0 
c 
8 

.o 10 
.008 
.006. 
.004 
-002 
0 -  
Off 0 
On 0 
Turbulator tape 
I 
4 
- 
- 
.2 .4 -6 .8 1.0 
Figure 3.- Drag and Lift Coefficient Variation (Rn. of 3 million.) 
10 
Cd .006 = O o 8 I  
I - - '  
0 SPL=130 dB 
W/O Noise - - -  
0 
I I I I J 
1 2 3 4 5 6 x I O 3  
.004 L l  
Frequency (Hz) 
- -  
Cd .006 O 0 0  
0 SPL=138 dB 
- - -  W/O Noise 
.004 L '  I I I I J 
1 2 3 4 5 6 x103 
Frequency (Hz) 
Figure 4.- Noise Effects On Laminar Airfoil With Laminar Bubble 
(Rn. of 3 million and SPL of 130 and 138 dB). 
11 
.008 
Cd .006 
.004 
.008 
cd .006 
.004 
o SPL=138dB 
W/O Noise - - -  
00 0 0000 
O0 0 
I I I i i 
1 2 3 4 5 t; X I 0 3  
Frequency (Hz) 
o SPL=130 dB 
- - -  W/O Noise 
0 0  
00 
Frequency (Hz) 
12 
1 cd .006 - 0 
0 SPL=125 dB 
- - -  W/O Noise 
0 0  0 
BOo8 r 
- Q -  0- 
Frequency (Hz) 
0- Q- 
0 SPL=120 dB 
W/O Noise 
0 0  0 
.004 I I I I 1 
1 2 3 4 5 6 x103  
Frequency (Hz) 
Figure 6.- Noise Effects On Laminar Airfoil With Induced Transition 
(Rn. of 3 million and SPL of 120 and 125 dB). 
13 
.008 
I 
Cd ,006 
.004 
.008 
Cd ,006 
,004 
o SPL=115 dB 
W/O Noise - - -  
0 O O  
1 I I I I I n 
1 2 3 4 5 6 xl0' 
Frequency (Hz) 
0 SPL=110 dB 
- - -  W/O Noise 
I I I I 
n 
- 
1 2 3 4 5 6 xl0 '  
Frequency (Hz) 
Figure 7.- Noise Effects On Laminar Airfoil With Induced Transition 
(Rn. of 3 million and SPL of 110 and 115 dB)- 
14 
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16 
Standard Bibliographic Page 
1. Report No. 
NASA TM- 100505 
2. Government Accession No. 
~__. _. ~~- -. 
7. Aiithor(s) 
John G .  Shearin, Michael G .  Jones, and 
Robert A. Baals 
9. Performing Organization Name and Address 
NASA Langley Research Center 
Hampton, VA 23665 
_. 
17. KPY Words (Suggested by Authors(s)) 
Laminar flow 
Acoustics 
Skin friction 
Transition 
_____ - --_ 
12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration 
Washington, DC 20546 
- 
15. Supplementary Notes 
18. Distribution Statement 
Unclassified - Unlimited 
Subject Category 7 1  
- 
3. Recipient’s Catalog No. 
19. Security Classif.(of this report) 20. Security Cla.cisif.(of this page) 21. No. of Pages 
Unclassified 1 7  
September 1987 
22. Price 
- A0 2 
6. Performing Organization Code 
~ 
8. Performing Organization Report No. 
10. Work Unit No. 
505-60-31-07 
11. Contract or Grant No. 
13. Type of Report and Period Covered 
Technical Memorandum 
14. Sponsoring Agency Code 
John G.  Shearin and Robert A. Baals, Langley Research Center, Hampton, Virginia. 
Michael G. Jones, PRC Kentron, Inc., Hampton, Virginia. 
16. Abstract 
A two-dimensional natural laminar flow airfoil (NLF-0414) was subjected 
to high-intensity sound (pure tones and white noise) 
range of 2 to 5 kHz, while emersed in a flow of 240 ft/sec (Rn of 3 million) 
in a quiet flow facility. Using a wake-rake, wake dynamic pressures 
were determined and the deficit in momentum was used to calculate a two- 
dimensional drag coefficient. Significant increases in drag were observed 
when the airfoil was subjected to the high intensity sound at critical 
sound frequencies. However, the increased drag was not accompanied by 
movement of the transition location. 
over a frequency 
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Acoustic effects on profile drag of a laminar flow airfoil

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