C.P. No. 262 C.P. No. 262 (17.502)

A.R.C. Technical Report (17.502)

A.R.C. Technical Report

MINISTRY OF SUPPLY

AERONAUTICAL RESEARCH COUNCIL

CURRENT PAPERS

Flow Direction Measurements in Supersonic Wind Tunnels

BY

D. J. Raney, B.Sc.Eng., A.C.G.I., D.I.C.

LONDON. HER MAJESTY’S STATIONERY OFFICE

THREE SHILLINGS NET

3 8006 10038 0719

C.P. No.262

U.D.C. NJ. 533.6.071.4.011.5

Techuoal Note No. Aero.23.2

Septeinber, 1954

ROY& i;L‘icitE u~SXLiLiT

Flow tirection measurements in supcrconlc vind tunnels

by

D.J. Heney, l3.Sc.Eng., A.C.G.I., D.I.C.

Some general requrements for satisfactory flow direotlon measurements in supersonic tunnel s are stnted ad cxaqlas are gxven of the dcslgn and calibrations of typical yaweter:;. 'Cne results of flow due&ion measurements rude 3.3 two turlr.els arc given 3-d some of the flow characteristics are dlscusstd.

1 Introduction

2 Senersl Requirements

3 Yaweter aceigns

3.1 Dlrcct reading yawmetex 3.2 Indirect rending yavmeters

4 Results of tunnel calibrations

4.1 R.A.E. No.6 Tunnel (% = 2.5) 4.2 R.&E. No.18 Tunnel (X = 1.51)

5 Discussion

References

Change in flow direction with increment of Mach Numhcr

Yawmeters used for tunnel calibrations

Sensitivity of conical yawmeters

Yawncter calibrations atn,os;,hcrx &o~natx~n prcss,ure

Flow darcotion mensurement~ in the K.A.R. No.6 (5 ln x 1-I in) tunnel at M = 2.50

Floxdixctlon measurements In the I! A.E. No.48 (9 m x 9 in) tunnel It! = 1.61. Angle of pitch in horizonkl pl.we through tunnel G,

Flov: direction measurements in the R.A.E. iTo. (9 in x 9 in) tunnel 14 = l.Gl. Angle of yap in horizontal plans throqh tunnel (&

Flow direction measurements m the R.A.E. No.18 (9 in x 9 In) tunnel X = 1.61. Arq:le of pitch in vertical plane through tunnel 0,

Flow direction mensurcments m the R.A.E. No.18 (9 in x 9 in) tunnel K - 1.61. Angle of yaw in vertiwl plane through tunnel Ci,

Resultant flow direction at a section through the R.A.E. No.18 (9 in x 9 in) tunnel N = 1.61. 2.9 in. upstream of vtidow Q,

F&

1

2

3

4

5

G

7

8

9

IO

-2-

For normal use in tunnel calibrations this design of instrument has msny advantages over direct reading yawmeters and is almost univer- sally prsferred. They arc simple to rnakc compared to the direct reading vane type and the use of oomplox swivelling gear is avoided. They oan be made small enough to Lnablo several to be mounted on a comb which enables tunnel running time for a calibration to be reduced. The differential pressure yavaneter can also be adapted fairly simply to measure both k&h number and flow directions in two planes2.

Fig.2 shows three designs of yavmeter henJs used at R.A.E. Though the scnsititity increases Vntii anex onglc as shown in Fig.3 the son& tivity of the 15O angle cone is adequate for most purposes. Hence the choice of design rests more on other considerations, e.g. ease of manu- facture or availability of some sort of multibore tubing. Another problem is to avoid the mutual interference of pitch end yaw. This was largely the reason why one group chose a pyramid head as opposed to a conical head. With conical or hemispherical heads the positions of the pressure holes must be accurately located in two perpemdiculcr planes passing through the axis of the head. With a pyrsmid shaped head the flow is less three dimensional in character and therefore the exact position of the holes is less critical.

The addition of a pitot tube along the ccntrt cf the multibore tubes used in the msnufaoture of the 900 opc~ angle heads would make them suitable for measurement of both hIach number rind flow direotion. It is worth noting that even without a cmtral pitot tube, the four-tube conioal yavmeter head can be used to measure Xach number by averaging the pressure measured by the four tubes to obtain the svcrage pressure on the

9 end end

deducing the Zach numbor from theoretical results for yawed cones .

Calibration curves for the three yawmeters shovm in Fig.2 are given in Fig.4; they are all linear even .&en the shook is detached as in the case of the 900 pyramid head at M = 1.6. Flg.3 includes these results and other published and unpublished results. Assuming that a water manometer can be used to measure differtntrsl pressure toz0.05 in. water the error in determining the flow direction is+O.O25o vLth the 15' yawn&or and +O.Cl" with tho 9C" conical. yawrrcter. Thcsc acouraoies are adewate, especially the latter. For convenience at the time, a mercury manometer KS used for celibrating the PO0 pyremid head. Assuming the pressure difference can be measured to 0.02 in. mercury the possible error istO.CJtO in flow direction. This is barely s&isfactory; a water manomettr should have been used. These VSCLULS would represent the order of scuraoies of comparative mcasuremcnts for one scttlng of the head. The error in setting the head is at least ~0.1~ and this therefore determines the error in absolute flow angle.

4 Reallts of tunnel calibrations

The results of some brief calibrations made of two anal1 tunnels are given. The tunnels are the R.A.E. No.6 tunnel end No.38 tunnel. The following table shows the total variations (neglecting the effeots of wandow joints on yaw) measured in pitch (Aa ) and in yaw ( Ag).

Tunnel Mach Working Total variation

Number Section Size Aa degrees Ap degrees

R.A.E. No.6 2.50 6 in x 11 in 1.5 0.Y R.A.E. No.dC 1.61 9 in x 9 in 2.5 2.0

* Excluding indicated flow angles close to the sidewalls.

-5-

-6-

+O.l’) The largest uncerteinty in flo~f direction measuranentn (about

1s 111 the basio setting of the yavmoter; this does not, of course, affect oomparative measurwnents made with the ssme setting.

Care should be taken in yawmeter measurements to ensure that the nose shock is either attached or detached for any given set of measure- mnts. Experience has shown that attachment or detachmat of the shock gives a ohangc in calibration,

Some interesting features are shorn by the yawetcr calibrations of two tunnel3 presented in section 4.

There are more ;ninor irregularities in pitch thsn in yax. Those in pitch arise from small irregularities in the nozzle surface. The side walls are of steel end were machined flat and therefore do not nomally cause small random irregularities II~ flow. In the calibration of the No.18 tunnel bad window joints in the side walls caused serious disturbances in the flow and in this size of tunnel it appears that steps at window joints should bc: less than about 0.031 in.

The calibration of the No.6 tunnel shows a strong in-flow from the walls townrds the oentre line in the vertioal and transverse planes. No explsnation can be offered but it indicates the need for flow direction calibrations off the centre line.

Some degree of rotationel flow has been meaeured in a number of low speed tunnels (see for exfwplc Ref.1,). These have been attributed to either the fan or to turning vL?I1es at comers. :\ieasurements in the No.18 tunnel show that, in spit.2 of the large cantraction ratio, scme rotationel flow may slso exist in a supersonic tunnel. The measuranants reported here indioate a rotational flow having a result-snt angle of about lo.

This last feature of the flow in the X0.18 tunnel shows how importout it is to meIce yavsneter oalibrations of supersonic tunnels, The exlstancc of the rotation of the flov: would not have been suspected from pressure measurements (Kcf.1).

& Author

I W.T. Lord D. Beastall

2 L.J. Beecham S.J. Collins

3 A.H. Stone

4 V.M. Paulkner H.L. Nixon

Title, etc.

Cah.bratlon of the FL&E. No.18 (9 m x 9 in) supersonic xwtd tunnel. P*&c I. Preliminary investigations. mr;-ent Paper 162. St&ember, 1553

Static snd dynamic response of a design of differential pressure yaweter at supersonic speeds. R.A.E. Report No. G.W.19.

On supersonic floss past a slightly yawing cone. Journal of &thCEnatics and Physics. Vol.27 No.1.

Experiments on airflow in the 7 ft opm jet No.1 tunnel and ~application to wind tunnel design. R. & M. 2L84. jamart', 1 :dt7.

Nf.2078.CP.262.63 - F’nnted In Great Bntasn.

0.C

CHANGE IN

FLOW ANGLE

(DEGREES)

0.4

O?

02

01

0

‘\. ‘\.

‘#I \ ‘#I \ . .

I I \ \ I I - -

I 2 3 4 5 6 7

MACH NUMBER

FIG.1. CHANGE IN FLOW DIRECTION WITH INCREMENT Of MACH NUMBER.

(0) 15’ CONICAL YAWMETER

(b) 90” CONICAL YAWMETER ’

(C) 90” PYRAMID YAWMETER

FIG.2 (a-c) YAWMETERS USED FOR TUNNEL CALIBRATIONS.

IO PRESSURE

Orff ERENCC

(I* WATER) PER DEGREE INCI OENCE

AT ATMOSPHERIC STAGNATION

PRESSURE

5

I -

. t I I

62* (YAWMETER WITH CENTRAL PITOT)

THEORfflCAt CURVES (REF 3)

0 E%PERIMBNTAL POINTS APEX ANGLE = SO”

’ MACH NUMBER 4 5

FIG. 3. SENStTIVlTY OF CONICAL YAWMETERS.

n 0

Y 90” CONICAL YAWMETE z 2 UJ k 60

2 s 2 r:

(c) 90” PYRAMID YAWMETER

0 YAWMETER ANGLE, 8

’ ’ NOTE DIFFERENT SCALES

FIG.4 (0-c) YAW METER CALIBRATIONS. ATMOSPHERIC STAGNATION PRESSURE.

I-

CL”

O-

PO0

-I -

I I +Ue PITCH UPWARDS +2h YAW TO LEFT (LOOKING DOWNSTREAM)

PITCH

I \ -

YAW

j-0, z=o I

(a) AXIAL TRAVERSE ALONG TUNNEL t.

-J----l LATERAL POSITION

FROM i)

I

I 51DE WALL

I ’

x=0, z--o

.I

(b) LATERAL TRAVERSE AT END OF NOZZLE

TOP LINER

BOTTOM LINER

VERTICAL POSITION

I-l x=o,po

I

CC> VERTICAL TRAVERSE AT END OF NOZZLE.

FIG.S.(a-c). FLOW DIRECTION MEASUREMENTS IN THE R.A.E. NO.6 (6”~ II”) TUNNEL AT M = 2.50.

I”

I

t d-0’ ANGLE

OF

PITCH

( + VE UPWARDS>

dc;O”

/ 3 IN TO LEFT OF k

( LOOKING DOWNSTREAM)

I . /- -1

I IN TO LEFT OF ‘k

I IN TO RIGHT OF k

d=O”-

3 IN TO RIGHT OF ‘&

-5 -4 D15TANC;3DOWN5TR& FROM i’kDOW ‘i (CINCHES)

I 2 3

FIG.6 FLOW DIRECTION MEASUREMENTS IN THE R.A.E. NO. 18 (9”X q)TUNNEL; tVl=1.61. ANGLE OF PITCH IN HORIZONTAL PLANE THROUGH TUNNEL &

t P .lj ANGLE OF

YAW (PIETO Em)

/3=d

TRACES OF DISTURBANCES FROM WINDOWS

l IN TO RIGHT OF &

\

/’ ;,I,, 3 IN. TO RIGHT OF & -5 ” -4

DISTANCE Z~WN ~TREZ FROM vkxw i (PNcHES) I z 3

FIG.7. FLOW DiRECTION MEASUREMENTS IN THE R.A.E. NO. 18 (h 9”) TUNNEL; M= 1.61. ANGLE OF YAW IN HORIZONTAL PLANE THROUGH TUNNEL ‘t.

d=d AN6LE

OF PITCH

(+VE UPWARDS)

d=d

I I I I I

/-----

- -/w

/ /

2

0

-L/v DISTANCE DOWNSTREAM FROM WINDOW I

‘k (INCHES) 1

-5 4 3 -2 -I

-

3 IN BELOW k

FIG.8. FLOW DIRECTION MEASUREMENTS IN THE R.A E. No.18 (9’;( 9”) TUNNEL; M= i-61. ANGLE OF PITCH IN VERTICAL PLANE THROUGH TUNNEL t

1 DlSTURI3ANCE FROM REhOVEABLE

BLOCK IN TOP LINER

3 IN ABOVE k

--=-&4x 1

I IN BELOW k

ANGLE OF

YAW

(+VE TO LEFT)

P c 0”

TRACE OF LOCAL DISTURBANCE FROM BADLY FITTING WINDOW

\ \

!\ \

\ \ 3 IN BELeW k

I -

-5 -4 DISTANC;3DDWNSTRE~ FROM :INDOW k &CH%)

I 2 3

FIG.9. FLOW DlRECTlON MEASUREMENTS IN THE R.A.E. NC18 (9”~ 9”)TUNNEL; M = Id 61. ANGLE OF YAW IN VERTICAL PLANE THROUGH TUNNEL 4.

I I I”

-J!--..-- I o0 07”

d---

oG”----2F-

0 5O

VIEW DOWNSTREAM

VECTORS GIVE ANGULAR DEFLECTION OF A\RSTREAM FROM AXIAL DIRECTION

FIG.10. RESULTANT FLOW DIRECTION AT A SECTION THROUGH THE R A.E. NO 18 (9”d)TUNNEL.

2,9” UPSTREAM OF WINDOW t, h/l= 1.61.

C.P. No. 262 (17.502)

A.R.C. Technical Report

S.O. Code No. 23-9009-62

C.P. No. 262