This report presents the results of an investigation to determine the effect of boundary layer control on the lift and drag of an airfoil equipped with a backward opening slot. Various slot locations, widths of opening, and pressures, were used. The tests were conducted in the Five-Foot Atmospheric Wind Tunnel of the Langley Memorial Aeronautical Laboratory. The greatest increase in maximum lift was 96 per cent, the greatest decrease in minimum drag was 27 per cent, and the greatest increase in the ratio, maximum lift coefficient/minimum drag coefficient, was 151 per cent

Bamber, Millard J

Knight, Montgomery

English

NASA Technical Reports Server

--
,,. *f’4? /?
........---------..--:-----
,
.“$
z #
%-
—.
F
TECHNICAL NOTES . .
NATIONALIADVISORY COMMITTEE FOR AERONAUTICS
WIND TUNNEL TESTS ON AIRFO~L BOUNDARY LAYER CONTROL
USING A .BACK?A.RDOPENING 13LOT.
By Montgomery Knight and Mi~laxd J, Bamber
Lmgley Memorial Aeronautical.Laboratory
Washington
October, 1929
.
https://ntrs.nasa.gov/search.jsp?R=19930081087 2020-03-17T04:21:41+00:00Z
lNATIONAL ADVISORY COMMITTEE FOR AERONAUTICS.
TECHNICAL NOTE NO. 323.
WIND TUNNEL TESTS ON AIRFOIL BOUNDARY LAYER CONTROL
USING A BACKWARD OPENING SLOT.
By Montgomery Knight and Millard J. .Bamber.
Summary
This report presents the results of an investigation to de-
tgrmine the effect of boundary layer control on the lift and
.
drag of an airfoil equipped with a backward opening slot. Var-
iouS SIOt locations, widths of opening, and pressures, were
used, The tests were conducted in the Five-Foot Atmospheric
Wind Tunnel of the Langley Memorial Aeronautic~ Laboratory.
The greatest increase in maximum lift was 96 per cent, the
greatest decrease in minimum drag was 2? per cent, and the
greatest increase in the ratio, maximum lift coefficient was
minimum drag coefficient’
151 per cent.
Introduction
This preliminary report gives in brief the results of an
airfoil boundary layer control investigation made to determine .
the effect of slot location, size, pressure maintained on the
inside of the wing, and the quantity of air flowing through the
slot* These tests were made in the Five-Foot Atmospheric Wind
Tunnel of the Langley Memori~.Aeronwtic~ Laboratory, and
.
were a continuation of those described in Reference lo The
N.A.C.A. Technical Note No. 323 2
*
l
backward opening type of slot was.used because, in the former
tests, this type of slot, when not in operation, gave the least
d.et~imentsleffect upon the aerodynamic characteristics of the
airfoil. The complete results of this investigation will be
published in a later report.
Apparatus and Tests
The tests mere made on an airfoil equipped with a rearlva.rd
opening slot which was adjustable both as to width and location
along the chord. A sketch of the slot and its proportions is
shown in Figure 1*
.
The N.A.C.A. 84-M profile was used. A sketch of this pro-
file is shown in Figure 2, together with the locations of the
slot along the chord.
The hollow airfoil of 15-inch chord and 25-1/4–inch span
was mounted vertically between two large horizont~alplanes at
its ends. This arrangement gave practically two-dimensional
air-flow conditions, and made it possible to conduct the air
for the slot to or from the interio~ of the wing (b-ymeans of a o
mercury seal) without affecting the measurement of the forces~
The quantity of air flowing through the slot was measured by
. .
l
mems of an orifice meter.
The tests were divided int; five main groups:
1. -No slot.
2. Slot position 13.1 per cent of chord from L.E*
(1.97 in.).
..
N.A.C.A. Technical Note No. 323 3
.
.
3. Slot position
(4.88 in.)
4. Slot position
(8.09 in.)
5. slot position
(10.9 in.)
32.5 per cent of chord from L.E.
.53.9per cent of chord from L.E.
~2,6 per cent of chord from L.E.
For each slot position four widths of the slot mere tested:
1. Slot width 0.16~ per cent of chord (.025 in.).
2. Slot width 0.333 per cent of chord (.050 in.).
3. Slot width 0.500 per cent of chord (.075 in.).
4. Slot width 0.66~ per cent of chord (.100 in.).
For each slot position aud width, tests were made at Ilwing
pressureslfof -6, -2, 0, +3, 2, 6, and 12 times dynamic
pressure (q). ‘[llingpressure11signifies the difference between
the mean pressure inside the hollow
* of the test section.
For each slot position, width,
wing and the
and pressure,
static pressure
measurements
of lift, &rag, and slot air quantity were made at angles of at-
tack g = -6, 0, 6, 9, 12, 15, 18, 21, 24, 27, and 300..
The dynamic pressure was held constant at 4.06 lb. per sq.
ft. during the tests. This corresponded to an average air speed
of 40 m.p.h., and an average Reynolds Number of 455,000.
.IT.A.C,A. Technical.Note No. 323 4
Results
These brief results show the genera effect of pressure,
slot position and width on the
1. Increase in
2* Decrease in
3. Increase in
maximum lift coefficient (Figs. 3 and 4)
minimum drag coefficient (Figs. 5 and 6).
speed range ratio (Figs. ~ and 8). ‘
.
In Figure 9, typical lift and drag coefficients CL and
%J respectively, are plotted against angle of attack u , for8,
the plain airfoil and also fox the slot combination giving the
l greatest increase in maximum lift. TWo dreg curves are given
for the slotted airfoil, one being the drag coefficient ~, as
determined from drag balace measurements; the other being the
eifectiv”edrsg coefficient CD + ~SO CDS, a hypothetical
drag coefficient, when used in the equation p = *P SV3CDS,
gives the power required to maintain the air flow thzough the
slot to or from the inside of the airfoil. This power does not
include the losses in the blower or connecting air ducts, since
these losses will vary with different duct-blower installations~
For a particular installation the duct-blower losses must, of
course, be included in CDS or accounted for in some
able way in calculating the over-all wing efficiency,
vation of the coefficient CDS is given in Reference
other suit-
The deri-
1.
?
.
.. .
N.A.C.A. Technical.~ote No. 323 5
It-should be noted that the drag coefficient on the airfoil “
CD, is actually negative under certain conditions, but that
this negative coefficient is obtained..bythe expenditure of power
represented by CDS so that the airfoil has”an effective drag .-
coefficient equ~ to (CD + (&).
The ratio
CL naximum
(CD + CDS) minim~) may be considered as a figure
of merit for the various slot combinations. ,Since CL maximum
?
.
represents the low-speed condition and (CD + CDS) minim~. repre-
sents the high-speed condition, the larger the value of the above ‘--
ratio the laxger the speed range, and the better the w~g for
general -purposes..This criterion is practically independent of
aspect ratio.
minimum
to q,
tion in
In
1.
the above ratio, in every case, the
is that obtained at a wing pressure
vslue of (&
approximately
+ CDS+
equal
since this pressure gives, in general, the greatest reduc– =
minimum drag as shown in Figure 6..
comparison with the plain airfoil:
The greatest increase in maximum lift coefficient CL
.
maximum, was 96 per cent, with the widest slot (0.66~ per cent
chord)-looated at 53.9 per cent of the chord from the leading
edge and at the greatest wing pressure (32 q).
2. The greatest decrease in minimum drag coefficient.
(CD + CDS) rninim~, was 2? per cent, with the widest slot (0.66~
per cent chord) at ?2.6 per cent of the chord from the leading
r.
edge and at a wing pressure approximately equal to 1 q.
.
,. N.A.C.A. Technical IioteNo. 323 6
CL m~imum
3. The greatest increase in the ratio (CD + CDS) minim~ ‘
was 151 per cent with the widest slot (0.66~ per cent chord) lo-
cated at 53.9 per cent of the chord from the leading edge, “The
wing pressure in the above ratio for
(12 q) and for CD min$mum was about
“ test ~peed of 40 m.p.h., the quantity
per sq.ft. of wing area was 1.095 for
CD minim~.
.
CL maximum was the greatest
equal to 1 q, and at the
of air in cu.ft. per sec.
(YLmaximum and .#~ for
The above statements indicate the advantages that might be
gained by the use of a slot under the idesl condition of 100 per
cent duct–blower efficiency.
.
Langley Memorial Aeronautical Laboratory,
National Advisory Committee for Aeronautics,
Langley Field, Vs., August 15, 1929.
Re f e r enc e
1. Reid, E. G. Preliminary Investigation on Boundary
and sl Layer Control”by Means of Suction md
Bamber, M. J. Pressure with the U.S.A. 2? Airfoil.
N.A.C.A. Technical Note lio.286, 1928.
l
,
.
,.
.
P
N.A.C,A. Technical Note No.323 Fi”gs.1,2 .
Effective
.SIOt width
Air flow\
Fig.1 Diagram of adjustable slot. .-
K---Slot 72.6 ~—--
1
1 p? --slot 53.9 Z
~’”” * —--~
Fig.2 N.A..C..A.84-M profile with slot locations.
,. N.A.C.A. Technical
.
r
100 r —-.-—-.—i
.— -—-
80 0
F.—
/‘
60 —f
~
—-
40--— ~
20
0
L.E. 20
No.323 - Fig.3
.-+ -+--*
1
p
.. +—-----;.[ I
i i“
-,—+..----- ._-7.—_y +
+J---&:$=+–..-
—
“Slot location
40
in per cent
60
of’chord
80
from
Fig.3 Increase in maximum lift due to the
100’T.E.
various locations and widths.
.
.
l
. . . .
. .
+
—— — —. —.
ii
/
/
7
,.
I
-6 4
-2 0 2 4 6 8 10 12 g
~ing pzef3sure w“IP
Dynamic pressure
.
TQ.4 Incrazise h maximum lift due to slot at various width and wing pressure.
N,A.C.A. Technical Note No.323 Fig.5
*
.
30
.—.-—— .-.——.
20
.
L’TI
El
-m 10 \
s
Cl
+1
:0 I\ —.
.+
~
cdFf:
y
kc)
fi
E I
-20
-30 ‘
——. — .
L.E. 20
Slot location in per cent of chord
T*E.
Fig.5 Change in minimum arag due to the slot at various
locations and widths.
bN.A.C.A, Technical Note No.323 Fig.6
-2 0 2 4 6 8’
Wing pressure
.—— .—
Dynamic pressure
Fig.6 Chamge in minimum drag due to slot at various?
widths and”pressures.
b
N.A.C.A. Technical Note No.323 Fig.?
Wing pressur~ =
— .—
Dynamic presmre
Wing pressure
Dynamic pressure = Approx. 1
80
40
0
12 fOr CL
for (CD +
max.
CDS) min.
——
+
——.— —... .. .— ..—..- —
I
3
. -—.— .-—-- . .—.
~
!
I I I ,
L,~o 20 40 60 80 100
Slot location in per cent of chord
from L.E.
Fig.7 Increase in the ratio CL iIIaX.
(CD + CDS) min.
..—
.
T.E.
.
due to slot at various locations and widti~s.
,- .
. .
1
.
-6
-4 -2 5 2 4 6 8 10 12
wing presxura
– for CL -c
FIB.B lnCr~aSe in ~~e ~e.~io
*.:’””” due to slot at various ~idths and preBsuKJs.
n
i’-
.
b,
4
N.A.C.A. Technical Note No.323 Fig.9.
.
2.8
ttad aizfoil—
.—
/
2.6 / \ I
S1p wit-tn =
L .iS1o-tat 53‘9$92.4 IIU ITom L.@-. -
IL$
z
Wipg prc:Ss$re
“22.2 =12 , \ —
-1-1W Dy4WQ —.
c1
///j ‘--
t
0 4 102.0 — .— ..— .— .— .—
~ — . . -—
sl.~ —.— .
TJ
\/ —
~
I
-,d i
~1.6 —+- _l_~ 1 \,
I j;.I-l
~ f~
I
l-l
I I i:1.4 —-
~
I
! f
o . /
gl.2 I
1
/f–
/ be
/ i I
=&l.o - .
~1
v!?
–~ /~
I
+
.8
I ~u= {
w
/
/
; 96
a
.
ad
.4> “ “/
f—-
/ 1
.2‘, —
(
T —.
+
0 / T
_~o 00 60 120 180 240 ’300
Fig.9 Angle of attack, degrees
-1
.


Wind tunnel tests on airfoil boundary control using a backward opening slot

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server