The effects of roughness at high Reynolds numbers on the lift and drag characteristics of three thick airfoils

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Material Information

Title:
The effects of roughness at high Reynolds numbers on the lift and drag characteristics of three thick airfoils
Alternate Title:
NACA wartime reports
Physical Description:
7, 13 p. : ill. ; 28 cm.
Language:
English
Creator:
Abbott, Frank T
Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Publisher:
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:

Subjects

Subjects / Keywords:
Reynolds number   ( lcsh )
Aerofoils   ( lcsh )
Lift (Aerodynamics)   ( lcsh )
Aerodynamics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: In connection with studies of airfoils applicable to large high-speed aircraft, the effects of roughness on three 22-percent-thick airfoils were investigated. The tests were made over a range of Reynolds number from about 6 to 26 x 10⁶ for the airfoils smooth and with roughness strips applied to the surfaces. The results indicated that for the roughened models the scale effect was generally favorable.
Bibliography:
Includes bibliographic references (p. 7).
Statement of Responsibility:
by Frank T. Abbott, Jr. and Harold R. Turner, Jr.
General Note:
"Report no. L-46."
General Note:
"Originally issued August 1944 as Advance Confidential Report L4H21."
General Note:
"Report date August 1944."
General Note:
"NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were previously held under a security status but are now unclassified. Some of these reports were not technically edited. All have been reproduced without change in order to expedite general distribution."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003614465
oclc - 71259194
sobekcm - AA00006284_00001
System ID:
AA00006284:00001

Full Text

ACR No. L4H21


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WAR1I TIMll R EPO RT
ORIGINALLY ISSUED
August 194 as
Advance Confidential Report IAH21

THE EFFECTS OF ROUGES AT HIGH RETOLD INMUMBERS
ON THE IFT AMD IRAG CHARACTERISTICS
OF THREE THICK AIRFOILS
By Frank T. Abbott, Jr. and Harold R. Turner, Jr.

Langley memorial Aeronautical Labaratory
Langley Field, Va.


.t IP
'4y


WASHINGTON

NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of
advance research results to an authorized group requiring them for the war effort. They were pre-
viously held under a security status but are now unclassified. Some of these reports were not tech-
nically edited. All have been reproduced without change in order to expedite general distribution.


DOCUMENTS DEPARTMENT


N I .;>


NACAL


~ :Xi~


L 46


K










!TNCA ACR No. LTH21


NATIONi.L ADVISORY COr."TITTEE FOR AERONAUTICS


ADVANCE CIOPPIDElI'TI..L TPOr.T


THE 0EFF1TS3 O? ROUGHi, S3 AT HIGH 7E'._m.LDS FI'UI'BERS

Oi THE LIFT '!D DRAG CRT.-,,cTPTISTICS

OF THL TiT:2:. ATIRFOILS

By Frank T. Abbott, Jr. and Harold R. Turner, Jr.





In connection with studies of air' oils ap:l"cable
to lar-r' hij-T-sorj~:- aircraft, the eff-cts of ro:: 'hness
on three 22-'rercent-thick airfoils were invest!i ted.
The t3sts "vee -e'I over a -:rn.e of R.ynolds nvnlber from
about 6 to 26 x 1. *for *t+. a folf s s:nooth l.nd ,vth
roughnes-" stric- u-plied. to the surfaces. The results
indicated that for the :'ou.s.h'ned ..!dals the scale effect
was generall:- favorable.


INTRODT T ION


PreTious tests in the NACA two-djiiensional low-
turbulence nres3ure tunnel of thick air'foils with
roughened leadin. edjes (reference. 1) indicated that
the lift and dra3 characteristics of the thicker wing
sections, when accijdenially roui hened, would have an
important bearing on the choice of sections for large
high-speed airplanes. These tests vert; limited to
Re-colds numbers :iuch lower than the flight values for
such airplane, by the use of 2-foot-chord wooden models.

The desirability of externding the tests to higher
values of the ReFnolds number was ap.ar-enrt, and an air-
craft manufacturer subnittd three 5-f,:.ot-iidord models
of heav- r,3tal : onstruti'n for thils pur cse. The three
airfoil sections .:'ere: an 3;ACA 65(hi.2)-h22 ,irfo l; an
NACA 65(22 .)-1L22, Q = 1.0 (a-prox.) airfoil, where
"(arprox.)" refers to a slight thickening near the
trailing edge; and a 2.-percent-thick Davis airfoil.
These models were tested in the NACA two-di:aensional
low-turbulence oreszure tunnel in order to obtain lift








NACA ACR No. L4H21


and drag characteristics at Reynolds numbers up to approxi-
mately 26 x 10o6 ith smooth surfaces, with roughness
grains of various sizes on the leading edges, and in
some cases with roughness strips at various chordwise
positions.


TEST METHODS


All tests were conducted in the NACA two-dimensional
low-turbulence pressure tunnel, which is characterized
by an air stream of extremely low turbulence. The models
extended from wall to wall of the rectangular tert sec-
tion. Lift measurements were obtained by a manometer
arrangement that integrated the lift reaction of the
models on the floor and ceiling of the tunnel, and drag
measurements were made by the wadle-survey method (refer-
once 2). A correction of about 2 percent was applied to
the data for normal tunnel-wall-constriction effects.
Lift coefficients near maximum lift were further corrected
for additional tunnel blocking that occurs when the model
is partially stalled. These additional corrections,
derived from static-pressure measurements made along the
floor and ceiling of the tunnel, varied from 0 to about
10 percent. Tests were made at tunnel tank pressures
from 50 pounds per square inch to 150 rounds per square
inch and, at all times, the tunnel airspeed was low
enough to avoid compressibility effects.

The airfoils submitted by the aircraft manufacturer
had 56-inch chords, were of heavy metal construction, and
aicre painted to give aerodynamically smooth surfaces.
The two low-drag airfoils were tested first smooth, then
with various sizes of roughness on the leading edge, and
finally with 0.011-inch roughness grains at one or more
chordwise positions. The Davis airfoil was tested smooth
and with roughness grains of two sizes on the leading edge.

Tests were made of all three models, both smooth
and rough, at Re:nods numbers of approximately 6, 10,
14, 20, and 26 x 100.

The roughness sizes of 0.002, 0.00C, and 0.011 inch
represent the average size of the carborundum grains
used. The roughness was applied to the leading edge

CONFIDO9TIAL


CONFIDENT IAL









NACA ACR No. 14H21


by coating a strip from 5.50 to 5.75 inches wide, sym-
metrically spaced about the chord line at the leading
edge, with thinned shellac and sprinkling with carbo-
r.uldum grains until 5 to 10 percent of the area was
covered with grains. The roughness strirs at 20 percent
and 50 percent of the airfoil chord (0.2Cc and 0.5Gc)
were similarly applied but were 0.5 inch wide with the
forward edge of the strip at the specified chordwise
location.


RESULTS AND DISCUSSTO"

N.CA 65(L;.20)-1,22 Airfoil


The effects on the lift rand drag characteristics of
four sizes of roughnes3 anplied to the leading edge of
the FACA 65 (j20_)-!_22 alr!'oil section at a Re-mold3 number
of 26 x 106 are sbown fin fi.uro I'. T'e loss in maximum
lift tended to be? -radual with increasing roughness size,
but the increase in drni coefficient in the low-drag
range was not gradual. The application of shellac alone
to the leading edge caused a large increase in drag coef-
ficient in this range. The shellac, however, did not
decrease the lift coefficient at which the drag increased
sharply to extremely high values, whereas all other
roughness sizes on ths leading edge did.

The effects of the 0.011-inch-grain roughness at
various chordwise positions are shown in figure 2. There
was no large detrimental effect on maximum lift unless
the roughness was on the leading edge. This result is
attributed to the fact that at maximum lift the shape of
the pressure distribution causes transition on the upper
surface to occur close to the leading edge. The effect
of roughness, therefore, in the thick turbulent boundary
layer downstream of the pressure peak would be expected
to be small in comparison with the effect of roughness
in the relatively thin boundary layer at the leading
edge. The drag coefficients at low and moderate lift
coefficients increased as the roughness was roved toward
the leading edge, as would be expected from the accom-
panying forward movernent of transition. The roughness
strips at 0.20c and 0.50c, however, did not appreciably
affect the value o' the lift coefficient at which the
drag increased to extremely high values. At these


C OF IDENTIAL


COTiFIDFULTIAL








NACA ACR No. L4H21


locations, the boundary layer cannot be laminar at such
1ift coefficients because of the shape of the pressure
' ictributions.

The scale effect on the lift and drag characteristics
of three sizes of roughness on the leading edge is shown
in figures 3 to 5. These plots show, in general, a
gradual decrease in drag and an increase in maximum lift
with increasing Reynolds number that is, the scale effect
was considered favorable for all three sizes of roughness.


NACA 65(225)-422 (Modified) Airfoil

Lift and drag characteristics of the NACA 65(225)-422
(modified) airfoil are shown in figure 6 for four model
conditions; namely, O.O04-inch-grain roughness on the
leading edge, 0.011-inch-grain roughness on the leading
edge, 0.011-inch-grain roughness at 0.30c, and smooth at
Reynolds numbers of 14 and 26 x 100. The curves for the
model in a smooth condition are presented to show that
this section had a gradual increase in drag with increasing
Reynolds number that is, the scale effect was con-
sidered adverse in the low-drag range. This result
was probably caused by some slight surface irregularity
which, because of the small slopes of the favorable pres-
sure gradients of this section, make it unusually sensi-
tive to any surface defects and unfairness. It is thought
that lower drags than are shown for this section are
possible, but NACA 65-series airfoils (reference 2) which
are preferable to the one tested are now available.

The application of roughness to the leading edge of
the NACA 65(225)-422 (modified) airfoil seriously
decreased the maximum lift and caused a large decrease
in the lift coefficient at which the drag increased
rapidly. The greater part of the drag increment attri-
buted to the roughness grains was caused by the smallest
roughness size tested. The roughness strip at 0.50c did
not affect the maximum lift coefficient to any great
extent, because the flow over the top surface of the
airfoil at this high positive angle of attack had become
turbulent much nearer the leading edge.

The effects of 0.004-1hch-grain and 0.011-inch-
grain roughnesses applied to the leading edge at
Reynolds numbers from 6 to 26 106 are shown in fig-
ures 7 and 8, respectively. The scale effect was
CONFIDENTIAL


CONFIDENTIAL








1


C ONPIDE:.JTI-.L


. .. .. ~I .


SACA ACR :Io. L4H21 CO1!F'ID-I;TiTIAL 5


-nrerall- favorable, es-ecially in the case of the
drag coefficients, but became very small at Re-nolds
nujxbers of 20 to 26 x 106. Th.e increase with Reynolds
number of .t:- value of the lift coefficient at which
the drag coefficient increased sharply was especially
notable.


Davl.s .Airfoil

Lift and drag data for the Davis airfoil in the
smooth condition and with 0.C J'-inch-_grain -nd 0.011-inoh-
grain roughnesses anrlied to the lep:din7 e_,,e are pre-
sented in figure 9. A comp.i,-rson of the lift and ira,
curves obtained for the smooth r;.o.- l with th curves
obtai.ned with roughn ss on the mc-,.el shows that even the
smaller (0.002-inch grain) rouv-iss caused a loss in
mraximrL,_, lift coefficient of a0r,.:irimatel.: 0.1, a slight
decr-ease In lift-curve slo-2, .n;d a large increase in
drag throughout the r,.ng testd..

RSsiilts of tests with roughness grrins of 0.0'02
and 0.011 inch cn the loe.din ecge at Reynolds numbers
from 6 to 2: x 106 are presented in figures 10 and 11,
respectively. Scale effect on the drag coefficients
was favorable for both sizes of rou-.hness b')t became
small at eynmolds nu'r.ers of 20 nd 26 x 10l'. There
was a small favorable scale effect on the r:.aximui-lift
vsnlues un to Re'molcds nul.-'"ers of 20 x 106 and small
adverse scale effect for hot!h izes of rciugrhness at
Re,-molds nur.bers frcm 20 to 26 x 106.


.,r.:FARICON OF AIR-CTL 3.2CTIOUS


The-. dr s coefficient3 of ithe N.,IA 65(420)-422
airfoil section and t]b 'aMCA '',(2'-'25 )-4-22 (modified)
airfoil section with rou.hr-ess strip cf 0.Oll-inch
grain at 0.50c a-re ccrinparcd in ligaur- 12. In this
condition the extent cf the i-rinar 'ouni.lry layer
should be the samen for both sections -,t lift coeffi-
cients corresDo'niin.L to the low-dra ran.z for thc
smooth airfoils. The dr.j coefficients wcre rn arly
the seaie for lift coefficients be.o', atout'1.2; the
differences sho'.n are not ccns-'der-ed reAter thi:ni


- --- --- -








NA3A ACR "To. LI+H21


possible variations for tests with roughness. Fig-
.re 15 shows a simila-r conposrison for the three airfoils
tested with 0.011-inch-grain roughness on the leading
edge0. The !IACA 63(420)- 22 section was more resistant
t- se-,ara.ticn when rough than the ocher two sections;
that is, the lift coefficient at rhioh the drag coeffi-
clenrts rise share ly tu ver.- Ligh values was appreciably
higher for this section than for the other sections
tested. ,urne.?rous snanw.ise, dr:a3 surveys .vere made of
the three models i.,ith roughresj cn the leading edges.
These surveys showived t that the N'.CA 65(4.20)-422 airfoil
had no localized sep;.'ation up to moderately high lift
coeffi.cieni.3, thtit che ',A.A 65(223)-422 modifiedied) air-
foil shoved marked local serar-i.Gion at much lower lift
coeffici.nts, iuld that th:: Davis airfoil showed local
separ.ti.on at lift coefficients above approximately 0.8.

The c-ffectc on the drg zco-fficicnt at a lift 2oof-
ficient of 0. of vurionu. sizes of roughness on the
loading cd:.e for the- thre-e Ciroils tested are s-own in
figure 1.. All r.hree airfoils h:,dl ne-rly the s,-i-me drag
coefficient wh.i. rough -n.d th':: drag incr-ased very
little with increasing rougChn-ss c'iz:. A large increase
occurred, howcvur, fro! the s;ioothi condition to tho
smallest ss...e of roughr.ess.

Both the NACA low-drag airfoilz 'ere affected
by, roughnet :ss at thl rn.-h Raynrolds nu.iubcrs than
at the lo'er .,ynolds nu-,nlirs. This favor.utale scale
eff>Zt vi.:h th.: .:odels in a rou1h condition increased
the l.it cocffiicnts .t. 'hi.ch uhe d'rag cuefficiCnts
increased raridl.y to extrrmcnl7 high values by nearly 0.4
fcr the :ACA 65(2?2)-4!22 (mccifi..d) section an 0.2 for
ti.e U.,CA ';(420)- 22 section. The- Davis airfoil showed
practically no favor'ilc .scalso effect in this respect
although th- -cff,-ct on dr:-a coeffici.'nt at lower lift
coefficients -iiz favor:,blj.


CON0C LUS IO ,NS


Tcets of an NACA 65(I.O0)-Jl22 airfoil, an
:ACA (5(225)-L22 (:noidi.fied) airfcil, and a 22-percent-
thick' Davis airfoil, all .-ith -'ouhneuss strips on the
suirfaccs, indicated tht following conclusions:

1. In general, the stiroila with rour-ghess strips
showed favoralble scale effects over the Reynolds number


CONF IDESTIAL


C 0. IDE-I'TIAI.








NCA AC. iTo. LL.H21


range from 6 to 26 x 106'. This favora'.-i.l scale effect
.vwas particularly effective\ nin the 'ACA airf.:is in
inccreas ng tihe lift co.;ffic'.-t. -it ''hlien tha. dL-a
cocffi;Cle.:; increased sharjpl o r.c' hi'.h v-.lues.

2. At ;1all ani i:.o'erjte li-t coe'fizients, the
dr:.9g coffi i'i!.ents for cll the, sez.i, ns tc sted .vi'ch
le.ini c:-c e roa. -..eoe nv-.rl. ti' -. saj- for th. sa:.e
r-u _'han? 3 condition an: Le'Lolds neu:::.ei. ith rou-h-
nes scr'.s ,t 5 ;-, er c-;n of the cc d, the dra~ charac-
teri2 t .cs of the ':'. :'.CJ aidlf'l.li tesed lW.ere nearly
the s'ai:e except ,t r'e l,i-hL-t lift co_ fficient.

3. I'; re: .sin.- t.e size rf the r-u' -.ness ("rr.is
a.-nlied to ;:1. I" :.n" c,-...e '.. ..'e s i l- d cre ,.sed
the mr:;.axi..un ift c-efi; l :n,-. fot t .sizes tested,
but t'-., .i-',t.-.r -, t Df r. :-'r.-:. "7 icre-":ent caTS- Ly;
the rou' l '-3 n '*c :,- '. 1 : t.. t'.s s. listt rco.]-uness tested.

,.. The .or ; r.f ;.. -it of th ;iree airfoils in
pe]'v ittl:'. hi.-!i lift co-ffic;i nt ., '". c.;tain d withoutu t
e;:ccssiv.- 1-' hi :;h dri' fieffLcier nts '.:it trh i- di---, g edges
rL.u.h is as fciy.;3: th:e 1J-... 65( L23)-122 airfo:il, the
.iIA c 65(223 )-22 (mr:dirfifed) jrfol., n.21., th --22- :'c:-cent-
thi'cl; .-_vis -1airfoi .

5. The n .'xi un lift coAf'iciei.te ,o the !iCn air-
fjils tocted '.er r. ot affected to an-y ;reat x-:te.ic by
r'ou ;-.ne'-. ztr-is au 20 or 5 p.-rcmut cf the-i chord back
of t'h Icedin, edl,:.


Langle. irr.eorial .e.'rai' icai r.a. o'a or
l. .i nal ~a'visory Co.:. lt i; .?or .'.aronan utics
Langlcy Field, Va.


[RrF:Ri-'CES


1. Jaco:'s, Eastmian N., A01'ott, Ira :., and Davidson, L..lton:
Invsvti-.:ction of .tre:.ic Lcar. ing-s'Tde ou hn..ss on
Thic', L-'l.-Drag Airfoils tr Indicate Those Critical
to separation. N/'"A CB, June 1:4.2.

2. Abbott, Ira H., von Doc!hc ff", Altert E., and Stivers,
Louis S., Jr.: SurStrar-' of Ai-foil Data. NAC. ACR
No. L5C5, 19)45.


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UNIVERSITY OF FLORIDA

Si 1262 08104 979 2II
3 1262 08104 979 2


UNIVERSITY OF FLORIDA
DOCUMENTS DEPARTMENT
120 MARSTON SCIENCE LIBRARY
P.O. BOX 117011
GAINESVILLE, FL 32611-7011 USA


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