Lateral blowing from the tip of a low aspect ratio wing

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< ;:0:; H I\) V1

.

..

von KARMAN INSTITUTE

FOR FLUID DYNAMICS

TECHNICAL NOTE 25:

LATERAL BLOWING F-ROM THE TIP OF

A LOW ASPECT RATIO WING

by

U

T

O.W. H~IBY

and

J.A. VAN DER BLIEK

RHODE-SAINT-GENESE, BELGI~M

(2)

von KARMAN INSTITUTE FOR FLUID DYNAMICS

TECHNICAL NOTE 25

LATERAL BLOWING FROM THE TIP OF A LOW ASPECT RATIO WING

by

O. Wo H~IBY and J. AQ VAN DER BLIEK

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1. 2. 3.

4.

5. 1. 2. 3. 4. 5.

6.

7. 8. 9. 10, 11. 12. 13.

14.

15.

16.

17. TABLE OF CONTENTS Page Summary Symbols Introduction Apparatus

Results and discussion Conclusions

References

Table 1

LIST OF FIGURES

Model mounted in wind tu~nel

Location of pressure orifices Tip slot and duct configuration

Total head distribution through jet shee~

Velocity profile at model location

Spanwise pressure distribution at a= 8°

Spanwise pressure distribution at a= 32° Chordwise pressure distribution atn= 0.3 Chordwise pressure distribution atn=0.98

and a= 8° and a= 8° Pressure distribution on upper surface at a= 8°

without and with blowing (C~ = 0 and 1.25) Pressure distribution on upper surface at a= 32°

without and with blowing 'C~

=

0 and 1.25) Spanwise l i f t distribution at a

=

8°

Spanwise l i f t distribution ARL test

Variation of l i f t with incidence for various momentum coefficients

Lift curves obtained in ARL test

1 2 3 6 7 8

Variation of l i f t curve slope with momentum coefficient Trailing vortex displacement due to spanwise blowing

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SUMMARY

The pressure distribution of an aspect ratio two

rectangular wing with lateral blowing from the tip was measured.

It was found that lateral blowing increases the l i f t at all lateral stations with an extra l i f t increa~e near the tip. The stall angle of attack was little affected by lateral blowing.

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b e

c

~

c

p öp duct q. J 8 U a

o.

J n LIST OF SYMBOL8

full span of wing ehord length of wing loeal lift coefficient total lift eoeffieient lift curve slope

ehord length of tip jet slot (e .o. p.U.)U. o.c. J J J J ...al.=4~

1.

U 28 g . ..:..l g = momentum eoefficient 2 Pao ao bc

p - Poo

=

pressure coefficient

q

00

pressure ~n duet minus atmospherie 1 Uoo 2 dynamic '[Peo

=

1 p . U. 2 dynami c

-

₂ _{J J}

=

half wi ng area veloeity pressure pressure angle of attaek

thiekness of jet sheet

in free

~n jet

pressure stream at exit

non- dimensional spanwise eoordinate ,

y/~

non- dimensional ehordwise eoordinate. x/e air densi ty

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1. Introduction

By blowing high veloc,i ty a~r laterally from the tip of a low aspect ratio wing, an "air seal" is created preventing direct air leakage from the lower to the upper wing surface. Simultaneously the tip vortex is displaced

outwardlyo The result is an increase in l i f t .

Carafoli, Ref o I, developed a method of calculating

the l i f t increase due to a lateral tip jet and carried out

some experiments on a rectangular wing with an aspect ratio

of twoo

The present report contains the results of pressure measurements performed to study in more detail the effect of lateral tip blowing on the surface pressure distributiono

Af ter the present test was completed, it was learned that similar tests had been conducted at the University of Sydney, Refo 2, whereby the jet could also be inclined

downW'ards. These results for straight lateral blowing are given in this report for comparisono

The tests were conducted by the first author, Ref. 3, while studying at VKI during the academic year

1963-64.

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Apparatus

The test was earried out in the VKI low speed wind tunnel L-l, Ref.

4,

in its open test seetion eonfigurationo

A half model of aspect ratio two and airfoil seetion NACA 0015

was mounted vertieally on a eireular refleetion plate, Fig. 1. The model was made of araldite and provided with

43

pressure orifiees all on one side o The pressure orifiees were plaeed

in two spanwise and three ehordwise rows as shown in Fig. 2.

The internal dueting for the ti~ jet air supply is

shown in Fig. 3. The total head distribution in the jet sheet is given in Fig~

4.

The non-uniformity is presumably eaused by the shape of the dueting and a divider in the middle of the duet.

The velocit1 profile on the refleetion plate at the model loeation is given in Figo

50

The average dynamie pressure of the tip jet at the

slot location was determined from the measured reservoir

pressure in the duet and the statie (atmospherie) pressure at the jet exit, assuming isentropie flow relations •. This

dynamic pressure q. was used to determine the momentum

J

eoefficient C as defined in the list of symbols.

~

Flow visualization runs were made with wool tufts on the model and with a wool tuf.t grid behind the modelo

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3.

3. Results and discussion

table 1.

A list of all runs and test conditions is given in Only the major results are presented in this paper. The spanwise pressure distribution is g~ven for two chordwise stations in Figo

6

in the linear angle of attack

range and in Figo 7 in the stall regiono Figo 6 shows an

overall increase of -C with extra increase near the tip

p

with increasing momentum coefficient. The effect of blowing is more pronounced on the upper surface than on the lower surface.

At 80% of the chord an increase in ~ produced a decrease

in-C near the tipo This was probably due to a vortex created

p

by the sharp corners of the wing tipt whose existence was verified by tests with wool tufts Q With increasing C this

l-!

vortex becomes weaker o

The spanwise pressure distribution in the stall

reg~on, Figo

7,

shows essentially the same characteristics o

Between 20% and 30% of the span there is a small pressure drop on the upper surface which occurred through the entire stall region for ClJ

=

0 and ClJ

=

0 0250

The chordwise pressure distributions at n

=

003 and n = 0.98 are shown in Figo 8 and 9 for a= 8°0 The inviscid

theoretical pressure distribution, from Chapter

4

0

5,

Refo

5,

is shown in Figo

8

0

The chordwise pressure distribution near the tip,

n

=

0.98 is given in Figo 90 The sum of the upper and lower

surface pressure distribution is also given in Figo 90 For

C

=

1025 the load distribution is nearly triangular as lJ

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4.

assumed by Carafo~i, Ref o 1, for the load distribution on the jet sheet o For C

=

0 and 0025 the chordwise pressure

lJ

distribution near the tip of the wing is somewhat flat.

This is thought to be due to the vortex induced by the s harp tip corners. When the angle of attack was increased, the flat pressure distribution also occurred at the higher value of ClJ •

Fig o 10 and 11 show isometrie pictures of the pressure distribution on upper surface for 8° and 32° angles of attack. To avoid complicating the figures, only the two cases of ClJ

=

0 and 1.25 are drawn. These two figures illustrate the earlier remarks on the spanwise and chordwise pressure distributions.

Fig. II shows the flattening of the pressure distribution in the stall region.

The spanwise lift distribution at 8° angle of attack is shown in Fig. 12. The theoretical distribution for ClJ

=

0 is taken from Fig. 10 in Ref.

6.

The experimental curve is lower than the theoretical one for

n<005,

and this is

probably caused by half-model effects o Near the wing tip,

there is a slight upward tendency of the experimental curve. The re~son for this tendency is the previously mentioned vortex created by the .harp corners at the wing tip. The curves for ClJ

=

0.25 and 1.25 show the same tendencies as the spanwise pressure distribution curves at ~

=

0.2.

The lift distribution obtained by ARL, Ref. 2, with an aspect ratio three half-wing is giyen in Fig. 13. These results do not show the pronounced upward trend near the tip, presumably due to the lower maximum value of ClJ ' the larger aspect ratio and the lack of data over the outer 20% of the wing span o However, both Fig o 12 and 13 show a general increase of Cl with increasing ClJ plus an extra increase near the wing tipo

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5.

By integrating the lift distribution the total lift

coefficient was obtained, Fig o

14.

It appears that the stall

angle is little affected by lateral blowing. The ARL

r.esults, Figo

15,

do not contain data up to the stall angleo

The ARL wing was rectangular with aspect ratio three and hàd

an a-symmetrie profile, NACA

64

₂

-415

with a modified lower

surface near the ToEo

The lift curve slopes of the present and the ARL

tests are compared in Fig.

16

0 For the present aspect ratio

two wing.tAe lift curve slope is doubled for a C~ near

unity.

During a series of runs with a wool tuft grid at various positions behind the wing, the location of the wing

tip vortex was determined. The spanwise position of this

vortex in its rolled-up condition behind the wing, is given

as a function of momentum coefficient in Fig o 17. Lateral

blowing causes a large displacement of the tip vortex. This effect decreases with increasing angle of attack.

The lift increase due to lateral blowing may now

be considered as due to: 1) the sealing effect near the tip,

preventing drop off of li ft near the tip and 2) the lateral

displacement of the tip vortices, resulting in an overall

l i f.t increaseo In addition sharp suction peaks appeared to

occur at the tip due to the particular configurationo

One advantage of lateral blowing as compared to blowing from the wing ToEo (longitudinal blowing) is pre-sumably that the latter increases circulation around the wing with attendant increase in induced drag, while in the case of

lateral blowing the effective aspect ratio is increased. (due

to tip vortex displacement) and thus the induced drag should

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6.

4.

Conclusions

The effect of lateral blowing from the tip of a low aspect ratio wing on the pressure distribution was determinedo

The overall l i f t distribution is increased by lateral blowing due to the effective sealing of air leakage

around the tip. Furthermore the tip vortex is displaced

laterally, resulting in an additional lift increase. This is

believed to result in a more efficient way of increas~ng the l i ft than longitudinal blowing which increases the induced

drag.

In contrast to longitudinal blowing. the stall angle of attack was little affected by lateral blowingo

obseorvedo

For C >1 high lift peaks near the wing tip were l!

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5. 1. 2. 3.

4. 5 •

6. References Carafoli, E. Smi th, V. J . Simpson, Go Jo H~iby,

o

.

w

.

COlin, P. E. Abbott, I oH. von Doenhoff, Ao E. Scholz, N.

7.

The influence of lateral jets,

simple or combined with .1ongitudinal

jets, upon the wing characteristicso

3rd Congress ICAS, Stockholm, Aug o

27-31, 1962.

A preliminary investigation of the effect of a thin high velocity tip jet on a low aspect ratio wing.

Australi an ARC Rept . 56, 1957.

Aeron. Res. Lab. ARL Aero Note 1630

Lateral blowing from the tip of a

low aspe ct rat i 0 win g.

VKI Project Report 64-106, 1964.

(Unpub li she d.)

The low speed tunnel L-l.

VKI(TCEA) TM 8, 1960.

Theory of w~ng sectionso

Dover PUblications, New York 1959.

Beiträge zur Theorie der tragenden

Fläche 0

Ingenieur-Archiv, Bdo 18, p. 84-105,

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8.

TABLE I TEST RUNS

fre ssure measurements

pU c 106 m/sec 00 0036 U = 25.9 Re : I

-

=

X 00 _lJ

~

6P duct , 00 _:20 _:40 _:80 _:1>20 _:180 _:220 _:280 _!32° mm Hg \ 0 0 X X X X X X X X x 100 0025 x x x x x x x x x 215 0.5 600 1 Q25 x x x x x x x x x

Runs with woo1 tuft grid (11 10cati on s behind wings) pU c 10

6

U_oo

=

·10.7 m/sec Re

=

-

00

=

0015 x lJ

!6p

_duct.

Ä

00 !2° !4° BHg !8° !12° !18° :22 0 _{!28° !32°} 0 0 x x x 15 0.25 Je x x 36 005 x x x 90 1025 x x x

Runs with woo1 tufts on winf:1j surf ace pU c 106 U = 10 07 m/sec Re

=

-

00

=

0015 x 00 _lJ 6P duct

~

~m Hg 0 0 _:20 _!4° _:80 !12° !18° !22° !28° !32° 0 0 x x- x 15 ,0025 x x x 36 0 0

5

x x x 90 10 2 5 x x x .'

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1000

~

--400

200

400 --

-holf-wing

_UCD

0

model

~ 0 &f)

L\6

N

I

N

.r

r

\

circular reflec'tion

I'

plate

dimen sions in mm

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200 ~ 1.0 120 1.0 '4 ~ --, ~ ~ .~.

.'

. ~

..-~\

0 _.- . , . /

\

0

r-

:

CD N

1

lt'I

I

55 10 20 50 50

I

30! 20 [IQ

-

_.

_+-"

_.

0 .

__

. ₁ - I--. '4

I

Ol 0\ "0

I

Ol 0\ 0 _._~ 0 ~ -ot

I

0 '0 N ~ I

..

I 0

-+-

.

~

'4

I

0 0

I

CD

I

N I . ~

I

~

_I

~

reflection plate

~

dimensions in mm

'!r

(19)

1 gl _leading_~dg~ 0 ... _ - - _ " ! brass duet

~

I

0 U) ... / ' -

-/ wing of ~I araldite o GO o (0) 200

IJl

....

u CII ;: CII L.. .~~

I

_Ipressur~

~

7

1

₀ o~ t a P"y::: In ./ "$. dimensions in mm

(20)

G 4 2

o

I I

I

measured at ~ ~ ... 1)

=

1,5 , 'UCI) = 0 -~r ...

1\

symbol . 11 Pduct 0

I

v 100mm Hg 0 0 Goomm Hg

\

~o

~

"

\

_V

_\

j)

~ v

,

"""

~

,...

....

v ~

_~

0.2 0.4 0.6 O.S ~ 1.0

Fig.4 TOTAL HEAO DISTRIBUTION THROUGH JET SHEE T

to

1) 0.8 0,6 0.4 0.2 o 0.2

.

At lE,statior

~

0.4

~

0.6 0,8 U 1.0

U

oo At L.E. station

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- 3.0

Cp

-2.0 -to o -1.0

Cp

-0.5 o 0.5

symbol qJ. _{upper surface}

a 0 v 0,25

-lower surface 0 _',25 AT 20% of chord

}

. /

V

...

~

-

.-•

--

11-.. ~

i

-z:::

_~-

_1:--

_t"--=

+-=-~~ -,=-~-0.2 0.4 0.6 0.8 ₁₁ _'.0 AT 80 % of chord J!. ...ó Ob 014 06 08

-;r

_1~

Fig.6 SPANWISE PRESSURE DISTRIBUTION AT a. = 8·

SymbOl1 ClJ. a 0 v o 0,25 ',25 upper surfa ce lower surface - 3.0r---=;=::=::;===;:=--.-_-,-_---.-_...,-_...-_..,.----,

C

p ,[

--l--+~~~~1--l---J--r-_r~

AT 20 % of chord

-2°1

I

I I I I I I

V

-tOl

J

j

~

j i j

+tb,

~~

o~ 1111ttl=i~;;t

_~_----+-- _~_~_"1""""=_~_• 1.0 L , _L-1_-.L_L-L_~----1.._--L.--_L--_ -1.5

Cp

-lO -1.5 o """ v 0.2 T I AT 80% of chord ~...-... 0.4 0.6

~

~ .---' ~ ~~

...

~

0.8 1) 1.0

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- 3.0 r - - - r - - - , , - - - , - - - - . . . , . - - - , Cp SymbOl1 q.1. o 0 v o 0,25 1,25 experiment - - - - theory(C~=O) 1~ql.~ ________ ~ ________ ~ __________ _ L _ _ _ _ _ _ _ _ _ _ L _ _ _ _ _ _ _ _ _ __

Fig. 8 CHORDWISE PRESSURE DISTRIBUTION AT

11

=

0.3 AND a.

=

8· symbol C~ o 0 v 0,25 o 1.25 - 3.0 _ir---,:======::;:=~--.___---t---,

upper and lower

surfaces separately

'J6

"

p... I - - - upper and lower

surtaces together -2.0

11 '" '" I

_"

\:

-1.0.,

_.

Y

_~

=+=9

_~- ~

_"

ol~-

-

I-

S:~~

to 1,1 _ _ _

--.l _ _ _ _

L _ _ _ ..l..-_ _ _ --l-_ _ _ _

Fig. 9 CHORDWISE PRESSURE DISTRIBUTION AT 1) =0.98 AND <I

=

8"

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- 3

Cp

-1

shaded area = inyréasel due to blowing

Fig. 10 PRESSURE DISTRIBUTION ON UPPER SURFACE AT ct = 8" WITHOUT AND WITH BLOWINS

(C~=O AND 1,25)

-2

Cp

shaded area =increase due to blowing

Fig. 11 PRESSURE DISTRIBUTION ON UPPER SURFACE '

AT

a.

=320 WITHOUT AND WITH BLOWI N 6

(C~ = 0 AND 1,25)

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", 1.4 Cl 1.2 1.0 0.8 0.6 0.4 0.2

o

I

symbol C~ experiment D 0 - - - - 'heO'Y(CIl:Ol7 r -Q _0,25 0 1,25

/

-

~

-

---

L-~

_~

"-'\

J 0.2 0.4 0.6 0.8 1\ 1.0

Fig. 12 SPANWISE LIFT DISTRIBUTJON AT ct = SO

1.0 Cl O.S 0.6 0.4 0.2 o a

=6-L

D

--~

/1

---W-

----

t-- ...

c~= O.SO

~

0,425

...

0.110 0

1 ...

,

'\.

"

\

0.2 0.4 0.6 0.8 1) 1.0

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1.6 Cl 0 1.4 symbol _CIJ. c ₀ 1';1 _0,25 0 _1,25 1.2 1.0 t - - - + - - - : l f - - ---t- - - + - - - I 0,8 t - - - - -- --+--I-- -- - - - t - r -- - - - ' \ - - + - - - I 0,6 t---I--+----.~_____,~---+---l ___ + _ - - - _ I 0,4 t---fl---+-+--+--- - - + - - - + - - - I Q2t---+-+~~-_r---___+---+_---_I

o

4 8 12 16 20 24 28 32 Cl

,D

eg

FIg,14 VARIATION OF LIFT WITH INCI DENCE FOR VARIOU5 MOMENTUM COEFFICIEN T5

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1.4r-____ ~~----_.---_T---_.---~---~ 1.0 1---~1__----__+----_J~--~~_+---I::....,....4---___1 0.81--____ ~1__----__+~+__,1_+~,El..---_+---_+---___1 0.6 f---lf---..,~_fI._.~_+---_+---__+_---_1 0.4 f---lf---u-+-,~---_+---_+---__+_---_1 0.21 ______ ~~----~---_+---_+---__+_---~ O~~ __ ~~ ____ ~ ______ ~ ______ ~ ______ ~ ______ ~ -5

o

5 10 15 20 25 (1,Deg

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Br---r---r---.---.

Cia

6~---~---~---+---~ 4~~~----~~---~---+---~ 2~---~---~---+---~ o 0,5 _1.0 1,5

Fig,16 VARIATION OF LIFT SLOPE WITH

MOMENTUM COEFFICIENT C~ 2,0 2,5 r - - - r - - - , , - - - , - - - , , - - - , - - - , 11 2.0 1---1r---1f---r---~~---1---r---1 1.5 ~----____1f----...",c_____1---__=_i-"""'----____1--==__..-.:==___iF---I 1.0 symbol

_a

..

theory tor C ~

=

0 0 4· 0.5 S" Q 0 12" 0 0.5 1.0 _C~ 1.5

Fig.17 TRAILING VORTEX DISPL ACEMENT DUE Ta

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V.K.I. TN 25

von Karman Institute for Fluid Dynamics, 1965. LATERAL BLOWING FROM THE TIP OF A LOW ASPECT

RATIO WING, by O.W. H~iby and J.A. Van der

Bliek.

The pressure dist~ibution of an aspect ratio"2

rectangular wing with lateral blowing from the

tip was measured. It was found that lateral

blowing increases "the lift at alllateral

stations with an extra lift increase near the

tip. The stall angle of attack was little

affected by lateral blowing.

V.K.I. TN 25

Bliek;

The pressure distribution of an aspect ratio 2 rectangular wing with lateral blowing fr om the

blowing increases the lift at alllateral stations with an extra lift increase near the

V.K.I. TN 25

Bliek.

The pressure distribution of an aspect ratio 2

rectangular win~ with lateral blowing from the

blowing increases the lift at alllateral stations with an extra lift increase near the

V.K.I. TN 25

von Karman Institute for Fluid Dynamics, 1965.

LATERAL BLOWING FROM THE TIP OF A LOW ASPECT

RATIO WING, by O.W. H6iby and J.A. Van der Bliek.

The pressure distribution of an aspect ratio 2 rectangular wing with lateral blowing from the

blowing increases the lift at alllateral stations with an extra l i f t increase near the