NASA-CR-177361 

19860003819 

A Reproduced Copy 

OF 

LIBRARY COpy 

LANGLEY RESE .. kt ,... ClN I ER 

LIBRARY. NASA 

lAIII('Ln STATION 

HAMPTON, VIRGINIA 

Reproduced for NASA 

by the 

NASA Scientific and Technical Information Facility 

FFNo 672 Aug 65 1111111111111 1111 11111 111111111111111 11111111 

NF00674 
--~ 

..-

I 

I -

/ 

! 

V 

f 

/ 

, 

... , 

'/ 

I 

/ 

( 

I 

! 

I 

, , 

/ 

/ 

1-. L 

} I 

I , I . I 

. ,/ J , , , , 

. ;! . , f , 

-I , 

.' 

1 Report No. I 2. ~I-II ~ No. 3. RIdpIeM'I CIIIIat .... 

NASA CR 177361 .. T,tle end Subtitle " ....... 0... Effects of Velocity Profile and Inclination on October 1985 

Dual-Jet-Induced Pressures on a Flat Plate in •. ~"*" ar.., iDtIoII CNt 

a Crosswind 

7 Author(., .......... 00 .. 131 • ........ No. 

A. K. Jakubowski, J. A. Schetz, C. L. Moore 

and R. Joag 10- WaR Untt No 

• ""orllll"" Clrll"'DtMln N_end ~ T-7526 Department of Aerospace and Ocean Engineering 

Virginia Polytechnic Institute and State University 11 Cafttroa Of Gt.. .. 

Blacksburg, Virginia 24061 NAG 2-256 

13 Tyllt of RIpCWt _ ...... Coveold 

12 Spomorln. Apncy .., .... Mel Add,_ Contractor Report National Aeronautics and Space Administration 

Washington, D.C. 20546 14 Spanwlnt AeIncy CII* 

505-43-01 

15 SUppl ....... I.'y Nom 

Point of Contact: Technical Monitor, Kiyoshi Aoyagi, MS 247-1 

Ames Research Center, Moffett Field, CA 94035 

(415) 694-5047 or FTS 464-5047 

II Abltracl An experimental study was conducted to determine surface pressure 

distributions on a flat plate with dual subsonic, circular jets exhausting 

from the surface into a crossflow. The jets were arran§ed in both side-byside and tandem configurat~ons and were injected at 90 and 600 angles to the 

plate, with jet-to-crossflow velocity ratio of 2.2 and 4. The major objective 

of the study was to determine the eff~ct of a nonuniform (vs uniform) jet 

velocity profile, simulating the exhaust of a turbo-fan engine. Nonuniform 

jets with a high-velocity outer annulus and a low-velocity core induced 

stronger negative pressure fields than uniform jets with the same mass flow 

rate. Howevel, nondimensional lift losses (lUt loss/jet thrust lift) due to· . 

s'uth' nonulUform fet's' wt::re lower than lift losses due to uniform jets. Changing 

the injection angle from 900 to 600 resulted in moderate (for tandem jets) to 

significant (for slde-by-side Jets) increases in the induced negative pressures, even though the surface area influenced by the jets tended to reduce 

as the angle decreased. Jets arranged in the side-by-side configuration led 

to significant jet-induced lift losses exceeding, in some ~ases, lift losses 

reported for single jets. Jets arranged in tandem induced considerably lower 

lift losses t ,an side-by-side jets operat~d under the same conditions. The 

pressure fields produced by tandem jets featured rapid relaxation of the 

negative pressures behind the jets, which was suggestive of rapid jet decay 

rates. , 

17 Key Words (Su!l9flled by Aulhor"') lB O,strlbytlOt'" Stlt!!m~nt 

Dual Jet ~n a crossflow Unclass~f~ed 

- Unlimited 

Pressure distribution 

Jet induced effects STAR Category 02 

19 Securltv 0-11 (01 tilts reporl) 

1

20 Secur,ly 0-1 fof 1"-..... ) 121 

No 01 ...... In Pnce' 

Unclassihed Unclass1fied 46 

'For sol. by the Nallonal Tacllrllcallnlormal,on Service. Sonntfleld. Vlrglnl, 22161 

I 

~r 

I I 

! 

! 

I -
. - -

. "'- ; I .,t'0 ,\ "",. 

\ ...-- -..-

... 

• 

NASA CONTRACTOR REPORT 177361 

Effects of \'eloc1ty Profile and Incl1n'ltion on 

Dual-Jet-Induced Pressures on a Flat Plate in 

a Crosswind 

'. 

, ' 

,11Sl-Ck-177l61) El'l,tS OP '£LOCIfr H6b-132e7 

PROPILE liD I~Cl1EltlO. 01 DUAL-JEt-IIDueED 

fiESSUBES 01 1 fliT fllTE II I CBOSSUIID ,'irq~D14 Polytechnic last. aDd state UaiY.) UDc14S 

52 p He 104/8' &01 CSCL 011 G1/02 01841 

A. K. Jakuholo"ski 

J. A. Schetz 

C. L. Moore 

R. Jo3g 

CONTRACT '\\r2-256 

Octoher 1985 

NJ\SI\ 

.. . .' 

, 

. 
,-

.. -

NASA CONTRACTOR RF.PORT 111361 

Effects of Velocity Profile and Inclination 

on Dual-Jet-Induced Pressures on a Flat Plate 

in a Crosswind 

," 

A. ~. JakubowRkl 

J. A. Schetz 

C. L. Hoore 

R. Joa~ 

Department of Aerospace and Ocean Engineering 

\irginia Polytechnic Institute and State University 

Blacksburg. Virginia 24061 

.. .. ' 

prepared for 

Ames Research Center 

under Gr~nt NAG 2-256 

October 1985 

NJ\51\ 

National Aeronautics and 

Space Administration 

Ames R~earch Center 

MoHel1 Field California 94035 

- -------

I 

I 

I 

I 

I .. ~ 

< 
. . . -... 

1 

ABSTRACT 

An experimental study was conducted to determine surface pressure 

distributions on a flat plate with dual subsonic. circular Jets exhausting 

from the sur~ace into a crossflow. The jets were arranged 1n both s1de-bys1de and tandem configurations and were 1njected at 90· and 60· angles to 

the plate. with jet-to-crossflow velocity ratio of 2.2 and~. The major 

objective of the study was to deter~ine the effect of a nonuniform (vs 

uniform) jet velocity profile. simu!~t!ng the exhaust or a turbo-fan 

engine. Nonuniform jets with a high-velocity outer annulus and a lowvelocity core induced stronger negative pressure flelds than un 1 form Jets 

w1th the same mass flow rate. However. nondlmensional 11ft losses (11ft 

loss/Jet thrust lift) due to suct. nonuniform Jets were lower than 11ft 

losses due to uniform Jets. Changin~ the 1njection angle from 90· to 60· 

resulted in moderate (for tandem jets) to significant (for side-by-s1de 

jets) increases in the induced negative pressures. even though the surface 

area influenced by the jets tended to reduce as the angle decreased. Jets 

arranged in the side-by-side configuration led to significant jet-i~duced 

lift losses exceeding. in some cases. lift losses reported for single jets. 

Jets arranged in tandem induced considerably lOwer lift losses than 5!de-byside jets operated under the same conditions. The pressure fields produced 

by tandem jets featured rapid relaxation of the negative pressure~ behind 

the Jets, which was suggestive of rapid jet decay rates. 

. . . . . .' . . .. . .. 
11 

SYMBOLS 

A nozzle exit area 

cp pressure coefficient. (P-P.)/Q. 

D Jet exit diameter (nominal) 

TL Jet thrust lift 

AL 

p 

Q 

q 

R 

s 

u 

x 

y 

ft 

.. 

e 

p 

Jet-induced 11ft loss 

static pressure 

dynamic pressure 

Jet-to-crossflow dynamic pressure ratiO 

Jet-to-crossrlow velocity ratio 

Reynolds number based on jet exit dianeter. p.U.D/~. 

Reynolds number based on distance from leading edge of plate to 

Jet center. p.u.t/~. 

.. . . .. . .. nozzle spacing 

velocity 

streamwise coordi~ate with origin at jet orifice center 

transverse coordinate with origin in the plane of symmetry of jet 

configuration 

coordi~ate perpendicular to plate with or13'n on plate surface 

boundary layer thlc~ness 

jet injection angle measured from flat plate 

viscosity 

density 

I 

f 

I 

I 

i 

I 

f , 

I 

j 

I 

I t 

\ 

J 

t 

l 

j 

I 

1 

'-
iii 

Subscrlpts 

• rreestream crossflow ..... r r ( o 0 

J Jet 

.' . 
... 

I 

INTRODUCTION 

Jets exhausting into a crossflowing stream are of considerable interest 

In several engineering applications including V/STOL aircraft 1n transition 

flight. vectored thrust nozzles. turbomachinery. combu8t~r8 and waste 

disposal. In the case of the V/STOL aircraft. Jets exhausting into a 

crosswind Interact with the adjacent surface of the aircraft Inducing 

pressure fields which are responsible for a 108s of 11ft and a change in 

pitching moment. Most of the prior relevant experimental work has centered 

on determining the pressure field around a single jet having uniform exit 

velocity profile [Refs. 1-5]. This pressure field was found to depend 

strongly on the jet-to-crossflow velOcity ratiO. R. Ooal- and/or multlpleJet configurations which may be 1mportant for advanced V/STOL concepts. 

Introduce additional effects c~~cerned with the jet configuration (tandem or 

slde-by-slde) and the mutual jet Interaction as a function of Jet spac1ng. 

Studies of these effects have been reported In Refs. 6-7. Another effect 

which plays an important role In certain VTOL and vectored thrust nozzle 

concepts conce"ns the jet Injection angle with respect to the crossflow. 

The first comprehensive Investigation of this effect for the case of dual 

jets. both tandem and slde-by-slde. has been reported In Ref. 8. 

With very few exceptions. VTOL engine exhau~ts have ~een Simulated by 

jets having un1form exit velocity profiles. While such an approach allows 

one to gain understanding of the jet/crossflow 1nteractlon and may be us~ful 

for making preliminary estimates of the pressure field developed on the 

surfaces surrounding jets, it does not account tor real jet effects such as 

nonunlformity of the exit velocity profile. swirling, and turbulence of the 

jet [Ref. 9J. These effects may have a significant influence on the induced 

pressure field and the resulting aerodynamic loads. The effect of the exit 

velocity profile may be of particular interest because actual VISTOL engine 

exhausts are expected to be strongly nonuniform. Kuhlman et al [Ref. 10J 

investigated the effect of jet decay rate on jet-induced pressures on a flat 

plate and used cyl)ndrical plu~s in.the je~ no~zle to vary the exit velocity . profile. ·They found that a nonuniform jet W1th a high velocity in the outer 

portion of the jet changes the induced pr'essure field and leads to a smaller 

nondimenslonal lift loss than a uniform jet having the same mass flow rate. 

Ziegler and Wooler [Ref. 11] used annular profile jets with either high 

velocity - or dead al~-cores: they employed jet velocity ratl0, R, based on 

the square root of the dynamic pressure ratio Iqj/q.. Their results 

displayed some differences when compared with the results of Ref. 10i at 

hIgher R values, the surface pressure distributions were not strongly 

affected by the shape of the exit profile. 

In the experiments discussed above, only a single jet was used, and the 

injection was perpendicular to the crossflow. There is clearly a need to 

investigate further nonuniform jets and to extend such investigations to 

dual jets and various injection angles. The primary objective of the 

present work is to obtaln information on the surface pressure fields induced 

by nonuniform dual jets arranged in either a tandem or side-by-side 

configuration and exhausting at different angles and different velocity 

ratios. Since the previous investigatlon of dual jets [Ref. 8J has shown 

that the mutual jet interaction diminishes rapidly when the nondirnensional 

jet spacing, SID. increases from 2 to 6, the jet spacings for these 
• 

2 

experiments was chosen to be S/0-2. Two Jet-to-crossflow velocity ratios. 

R-2.2 and 4. and two injection angles, a-90· and 60·, were selected. 

In addition to the main objective of this work concerned with the 

surface pressure measurements. tlowfield measurements were made to obtain an 

insIght lnto the lnteraction of the jets with both un1form and nonun1form r 

velocity profiles. These measurements were limited to the dual tandem jets 

exiting at 90· and involved mapplng velocity vectors in the plane of 

symmetry of the configurat1on. 

APPARATUS 

The exper Imerlts were performed in the Virginia Tech subsonic closed-· 

circuit Stability Wind Tunnel which has a test section 1.83 m x 1.83 m (6 ft 

x 6 ft). The tunnel veloclty ranged from 8.6 m/sec to 40.5 m/sec (28.3 

ft/sec to 132 ft/sec). The wlnd tunnel Is described in Ref. 12. 

The test model conslsts of a steel flat plate fitted with a 60.96 cm x 

71.12 cm (24 in x 28 in) instrumented sectlon (Fig. 1). The latter has an 

"L" shaped cutout to accommodate various nozzle and spacer sections to 

realize various injection angles and a variety of either t~ldem or side-byside jet configurations. The flat plate model has an elliptical leading 

edge and a tapered trailing edge. S1nce the model was des1gned for testing 

in the 2.13 m x 3.05 m (7 ft x 10 ft) Sub~onic Wind Tunnel at the NASA Ames 

Research Center, it was necessary to mo~ify one slde wall of the test 

section of the Virginil Tech 1.83 m x 1.83 m (6 ft x 6 ft) wind tunnel to 

allow a small part of the model to protrude. The flat plate _~s mounted 

40.64 cm (16 in) below the tunnel ceiling with the jets exhausting downward. 

The jet nozzles had a 4.93 cm (1.94 in) exit diameter. The center of the 

front jet nozzle was located 48.26 cm (19 in) behind the flat plate leadlng 

edge. The boundary layer on the plate was tripped using a 5.08 cm (2 in) 

wile strip of 100 grit sandpaper. . . . . . . . . . 

Each of the two air jets was produced by a set of two axial blowers; a 

larger blower rated at 40 m'/min (1400 CFM) supplied the outer, highvelocity portion of the jet, and a smaller one rated at 8.5 m'/min (300 CFM) 

supplied the inner, low-velocity portion of the jet. Both blowers were 

driven by DC electric motors; this allowed control of the mass flow rates by 

simply adjusting the supply voltage. The outputs of the two large &nd two 

small blowers, respect1vely, ~ere matched exactly by rheostat control of the 

supply voltage. The blowers were connected to the nozzles by means of 

flex1ble plastiC tubes. The nozzle assembly is shown in Fig. 2 for the cas~ 

of the 90 0 injection angle. The main components of the assembly are two 

concentriC tubes through which air 1s forced by the blowers, an injector 

chamber within the exit nozzle, and a removdble stream separation insert. 

This insert, attached to the inner tube, can be translated axially to 

control the separation of the inner, low-velocity stream from the outer, 

high-velocity stream prior to reaching the nozzle exit and, hence, to 

control the shape of the exit velocity profile. The jet exit profiles can 

be varied over a wide range of shapes by controlling the mas~ flow rates of 

the blower3 and adjusting the position of the stream separEtlon insert. A 

unifc"m velocity profile can be readily obtained by removing the separation i~sert and reducing th~ mass flow rate through the inner tube. 
-- - -. - -.-~--~-------

3 

The main instrumentation In these experiments consisted of static 

pressure taps whose layouts are shown In Fig. 3(a) and 3(b) for the slde-byaide and tandem Jet configuration, respectively. These layouts were chosen 

to minimize the overall number of the pressure taps. In addition, selection 

of the layout pattern was influenced by an assumption that for both jet 

configurations, the symmetry of the flowfield and the resultant surface 

pressure field would be good. The slde-by-slde configuration used a total 

of 312 pressure taps, while the tandem configuration employed 318 taps. 

Individual pressure taps were connected by long plastiC tubing to ten 

Scanivalves fitted with dummy transducers. The pressure output from each of 

the Scanlvalves was fed by a short line to one port of a 12-port wafer 

switch. The latter was connected directly to a single differential pressure 

transducer (PDCR-22) having a range of ±b.895 x 10' Pa (±1 psi). This 

measuring system, based on sharing a single pressure transducer, has a 

slower rate of data acquisition than a regular non-sharing system (with each 

Scanlvalve fitted with an active transducer), however, It offers an 

advantage of possibly higher accuracy, particularly when measuring small 

pressure differentials. All the pressures were referenced to the freestream 

(wind tunnel) static pressure. The step time from one pressure port to the 

next one was 2 seconds. This step time was established on the baSis of 

extensive preliminary experiments in which the ~ressures at selected 

locations were continuously recorded at a high rate. In most cases, fully 

stabilized pressures were reached after a period of 0.5 to 1 se~ond. To 

obtain a good mean value, the static pressures at each port were computer 

averaged during the last second prior to stepping to the next port. The 

pressure transducer was calibrated after every 46 consecutive pressure 

measurements. The calibration involved zero- and 1.00 psia - presSure 

readings. The 1.00 psia pressure was supplied by a preclse dead-weight 

tester. The updated calibration information was fed into the computer which 

processed the pressure data. 

IPl· -ad.ditLgn t.o 'surface .!'ressur-e me.as.ur.ements. ·pr.e:i\sures '~Pld 

temperatures were taken for the air flows of the Jets. tunnel freestream 

flow and the barometriC conditions. 

To obtain time-averaged velocity measurements 1n the plane of symmetry 

of the tran5versely injected tandem dual jets. a five-port yawhead probe was 

used. The probe was mounted on a traverse mechanism and was oriented at 450 

with respect to the flat plate. The probe was located about 51 cm (20 in) 

upstream of the attachment on the traverse mechanism and the effect of the 

probe support on the probe measurements was considered to be minimal. 

All the measured d3ta were recorded and processed by an HP 3052A Data 

Acquisition System. 

TEST CONDITIONS AND PROCEDURES 

The major parameters in testing dual jet configurations are jet-to- frce~tream velocity ratio (R). jet injection angle (0), and the jet spacing 

(5). Based on previous experlments with the same flat plate model [Ref. 8]. 

a constan~ dimensIonless jet spaCing, S/0-2, was selected; this was the 

smallest sp2cIng allowed by the experimental set up. Two jet injection 

angles. e-So o and 60 0 , were chosen. The range of jet-to-crossflow veloclty 

I 

I' 

',--
, ' , 

-... , .' 

4 

ratio was constrained by (a) the maximum output of the blowers and (b) the 

lowest wind tunnel velocity (about 10 m/sec (30 ft/sec» to develop 

turbulent boundary layer near the jet injection. The above two conditions 

determined the maxImum R value of~. For the lowest velocIty ratio R, a 

value of 2.2 was chosen, tor whioh experImental results obtained wIth 

uniform jets are available. The ~elocity ratio, R, was changed by varying 

the tunnel speed while holding the jet velocIty fixed. This procedure 

eliminated the difficulties assocIated with duplicating the nununiform jet 

velocity profiles at different jet speeds. 

The jet exit velocity profiles used in these experIments are shown in 

Fig. 4. These profiles were measured in the absence of the cro8sflow using 

a traversing Pitot-static probe. The nonuniform velocity profiles were 

selected to represent the case of a turbo-fan engine. The equivalent 

uniform-velocity jet had approximately the same mass flow rate as the 

nonun1form jet. To satisfy th1s condit1on, the equivalent veloc1ty of the 

un1form jet was determined from 

where u is t~e velocity and A is the nozzle exit area. It can be seen from 

Fig. 4 that the symmetry of the ~onun1form prof1le was better for the 

1nclined 1nject1on (9-60

0 ) than for the transverse (9-900 ) inject1on. In 

addition, the average velocity of the 600 jet was somewhat higher than for 

the 90 0 jet. This increase in the velocity was made possible due to small 

modification in the ducting connectin~ the blowers to the nozzle assemblies. 

By removing sections originally intended for mass flow measurements, the 

pressure drop in the duct lines was reduced, and the jet velocity was raised 

somewhat. This, in turn, allowed raising the tunnel velocity (for the 

experiments with 60 0 jets) which might have a favorable effect on the 

quality of data because of increased values of the measured pressures and/or 

possible imprOVement of the boundary layer characteristics. The tunnel and , 'Jet' ve16ci ties' u'sed 'in these experlrr.ehts 'are listed 1n Table 1. ' ' . 

The boundary layer profiles at the front nozzle location were 

determined by means of a 21-tube rake. The nondimensional profiles shown in 

Fig. 5 correspond to the tunnel Velocities used in the 90 0 tests. The 

freestream Reynolds number based on the surface dlstance to the front 

nozzle, Ret' was belOW a value required to ha~& natural transition and a 

fully developed turbulent boundary layer, so a sand paper strip tt'ip was 

used. The profiles in Fig. 5 appear to be typical for artific1ally tripped 

boundary layers. 

The jet induced pressures on the flat plate were determined as the 

difference between jet-on and jet-off conditions. The experimental 

procedure consisted of the following major steps: 

(1) reading surface pressures at a desired crossflow velocity with the jets 

of! and nozzles plug~ed with inserts flush with plate surface, 

(2) checking the velocity of each jet with the tunnel off by traversing a 

Pi tot-static tube 1n small increments along the x- and y-direction 

across the nozzle exit area, 

(3) recordlng surface pressures with the jets and tunnel turned on; the 

readings were started after the jet air temr ~ture had ste~ilized at a 

I 

• } 

i 

I 

1 

l 
\ \ 

TABLE 1 

Freestream and Jet Flow Conditions 

I Freestream Reynolds number Nonuniform jet Jet Jet-to-crossflow 

Jet velocity. m/s (ft/s) 

inclination velocity Tunnel Uniform jet Peak velocity in Av. velocity angle ratio velocity R.eo Rei outer region in inner core 

e, deg. R m/s(ft/s) (x10-5) (x10-5) 

2.2 15.7 (51.5) 0:45 4.4 

90 , 34.4 (113) 55.2 (181) 18.9 (62) 

4 8.6 (28.3) 0.24 2.5 ~ 

I " 

2.2 18.3 (60) 0.52 5.2 

60 40.2 (132) 58.8 (193) 23.5 (77) 

4 10.1 (33) 0.29 2.9 

-_ .. -

\It • 

I I 
(II> 

6 

constant temperature which was about 30·F higher than the freestream 

tunnel temperature, 

after the surface pressures had been taken, the tunnel was turned off 

and the jet velocities were checked agaln. ,0 

RESULTS AND DISCUSSJ1N 

The surface pressures induced by the jets are presented in the 

nondlmensional form as 

where cp.(P - P.)/q. and freestream values of the statlc (p.> and dynamic 

(q.> pressures are used as reference condltlons. Because of the symmetry of 

the jet/crossflow arrangement, the Induced pressure fleld was expected to be 

symmetrlcal. On thls basls, the actually measured pressure data were 

extended to a larger surface area by reflectlng the actual data polnts about 

the 11ne of symmetry in each configuratlon to generate vlrtual data polnts 

In the noninstrumented r9g10ns or the plate. Both actual and vlrtual data 

polnts were used to generate constant pressure contours of the induced 

pressure fleld. From inspectlon of Flg. 3 It can be seen that, for the 

side-by-side configuration. the virtual data points were generated in the 

right-hand portion of the flat plate surface, wnile for the tandem 

configuration, the virtual data pOints were created In the left-hand portion 

of the graph. Consequently, some cautlon should be exerclsed when analyzing 

pressure fields In those areas. 

Generating constant-pressure contour plots can be a tedious and tlmeconsuming task whlch, in addition, may involve an element of subjective judgemen~~· In an effort to all~Viate these proble~, we empleyed a Cal·Comp 

General Purpose Contourlng Program to trace out isobar contour maps. While 

the computer tracing worked quite well inside the regions covered by a large 

number of Input data pOints, the parts of the plots near the inner and outer 

boundaries were found to be unsatisfactory. Therefore, the contour maps 

presented in the following sections were made by hand plotting using 

computer generated layouts of the numerlcal pressure data. For details on 

computer plots see Appendix A. 

Jets Exiting at 90 0 

The surface pressure distributions obtained with side-by-slde jets 

exhaustlng at a-90 0 Into the crossflow are shown in FlgS. 6-9.* Generally, 

the pressure fields induced by the 90 0 jets display small regions of ~lightly positive pressures ahead of each jet and very large negativepressure region to the sides of and downstream of the jet nozzles. Lack of 

left-to-right sy~~etry (for each jet) of the pressure contours near the j~t 

exits indlcates clearly that the flowfie11s produced by the jets strongly 

*Broken lines represent contour sections determined by extrapolation of the 

measured data. 

• I 

t. 
. . .. -... 

I 

i 

7 

1nfluence each other; this results trom the ract that transverae jets induce 

large negat1ve-pressure tleld! projecting over large distances not only to 

the sides of the jets but in the upstream dlrection as well. 

The effects of increasing the jet-to-crossflow velooity ratio. R. trom 

2.2 to ~ can be seen by comparIng F1g. 6 with Fig. 7 and Fig. 8 with Fig. 9. 

For uniform velocity-protile Jets (Figs. 6 and 7), the negative-pressure 

region expands in nearly all directions. Based on the 8~rface area enclosed 

by the 6Cp--.3 11ne. this expansion is about 70$ of the area corresponding 

to R-2.2. For nonuniform velocity-profile Jets, the increase in the 

negative-pressure area, caused by increasing R, is smaller, ~stimated 

crudely at about 30$. and is characterized by a forward shift of the 

negative pressure center. The small positive-pressure regions ahea~ of the 

jets appear to decrease sIgnificantly when the parameter R is increased from 

2.2 to~. A similar effect of the parameter R on the Induced negativepressure field has been documented in previous experiments w1th single and 

dual jets exlting normally into a crossflow [Refs. 1-8). An increase in R 

causes the negative-pressure region to expand and the pressure center to 

move forward. 

A Simple physical explanation of the effects of the parameter R may be 

given by taking a close look at the mIxing/interaction process between a 

single jet and crossflow (Fig. 10). This mixing/interaction is a highly 

complex, unsteady process i~volving development of turbule~t structures of 

various scales and llfetimes at the jet/crossflow interfa~~e In a timeaveraged frame. the mixing/interaction reduces mostly to three major. 

interrelated aerodynamic effects [Ref. 9]: 

(a) the ~urbulent entrain~ent of air from the crossflow leading to, among 

other things. a rapid spread of the Jet. The entraln~ent of 

crossflowing aIr by the jet creates a low-pre~sure regIon around the 

nozzle and this effect becomes more pronounced as the parameter R . . . . i-ncr"ease·s:· ..... .. . 

(b) a pair of counter-rotating vortices formed 1n the jet as it e~erges 

from the nozzle; these vortices tend to control the downstream 

development of the jet. The effect of counter-rotatIng vortices 

influences mostly the surface pressure dIstribution downstream of the 

jet center. Since the vortices ar se, it is suggested, from the 

shear'ing action exerted by the crossflow on the sIdes of the jet as the 

latter emerges from the nozzle. the vortex strength is likely to 

increase with increasing initial upright distance and penetration (and. 

hence, with increasing R) of the jet before it i5 bent in the crossflow 

direction. Therefore, increasing R results in a growing vortex 

intenSity which in turn leads to larger induced veloc1ties and 

lncreasGd surface area lnfluenced by th~ jet. However. this trend 1s 

not expected to contlnue indefinitely. When R reaches and then eXCeeds 

a certain value (for instance, around 8), the effect of a further 

vortex strength increase will not be felt anymore on the surface 

because it becomes null1fied by the concurrent ~ffect of the vortex cente~line beIng displaced further away from the surface. If the 

parameter R continues to increase, the 1nitial trend in the effect of 

the counter-rotating vortices on induced surface pressures is expected 

to become reversed, resulting in reduced surface area influenced by the 

jet. 

/ 
° ° • 

-~- -------- -1 

8 

(c) a blockage effect caused by the jet and resulting in a near-surface 

wake behind the Jet. The blockage effect results in a posltlvepressure region ahead of the Jet. a streamwise acceleration (and. 

hence. lower pressures) near the s!des of the nozzle and d wake flow 

behind the Jet. where a significant entrainment activity takes vla~e. 

As R increases. the effect of the blockage tends to diminis~ (~xcept 

for th~ range of R less than about 0.5. which is of little importance 

to VTOL applIcations). and we may expect that the forward positiv~· 

pressure region and the acceleration neal' the nozzle s.l.lJes decrease. 

while the wake region will remain only weakly aff~cted. The overall 

effect of blockage on the surface pressures. corresponding to an 

increase of RI may be one of (1) positive-pressure region bec~ming 

smaller. (2) pressures near the nozzle sides becoming somewhat less 

negative. and (3) wake region remaining almost unchanged or Lo~ewhat 

reduced. primarily due to changes in the Reynolds number based on 

crossflow co~ditions and the nozzle size. 

Summarizing the individual effects of entrainment. the vortex pair a .. d 

blockage it is concluded that the expected resultant changes in the surface 

pressure field. when R is increased. are as follows: 

(1) the negative-pressure regions to the sides of the nozzle expand 

until a certaIn R is reached. beyond which a reverse trend may be expected. 

(2) the generally small po~itive-pres5ure region ahead of the Jet 

decreases continuously, and 

(3) the ~ffecti ve center of the preesure field which at low R values 

is located downstream of the nozzle. moves continuously forward. approaching 

the nozzle center at high R values. This trend is suggested by the fact 

that at hIgh R values. the entrainment effect which, per se, tends to 

develop a negative-pressure field symmetrical with respect to the nozzle 

center. becomes very likely the main contributor to the pressures over most 

of the surface except fo~ the regions ahead of and behind the Jet nozzle 

wpere the blockage effects dOminate. Wh\le tpe discuss40n Just preserttEd 

°refers °to a singOle °jet, Similar arguments may be applied to a case of dual 

jets. 

Returning now to C'ur results o;;nown in Figs. 6-!:j, it can be seen that 

the experimentally observed tren(.s are consistent with the physical 

explanation given ill the preceding discussion. Since no data were obtained 

for R values higher than 4. the prediction concerning the behavior of the 

pressure field at high R could not be verified. However, careful 

examination of the pressure plots in Ref. 8 indicates that while an increase 

of R from 4 to 6 resulted in a significant increase of the surface area 

influenced by the jet for both tandem and slde-by-side dual jet 

configurations, a further increase of R from 6 to 8 seemed to produce a 

slight contraction of the jet-influenced surface area fOI' tandem jets, and 

only a small or moderate expansion of this area fer the slde-by-sid~ jets. 

The influence of the jet velocity pr':lflle cn the pre<Jsul'e fields 

induced bJ the 90 0 jets can be seen in Figs. 11 and 12. The nonuniform 

veloclty-pr0file jets induce larger negative-pressure regions (and smaller 

upstream positive-pressure regions) and the pressures near the jet nozzles 

are consistently lower for such jets. At R-2.2. the negative-pressure area 

(enclosed by the 6C --.3 line) Is abo~t 50% larger for the nonuniform Jet-, p 

and at R-4, this increase is roughly estimated at about 20%. It can be ~een 

i 

I 

I' 

I 

, 

.. 

.~. 

I 

L" 
~ ~ - , . \ , 

I \ 

\ 

" 

. - - -- -

, 

: 

1 

9 

that the trends of these changes are the same as those which result from 

Increasing R. It is suggested that these changes may be explained as 

tollows: 

The nonuniform jets used 1n this study have significantly hIgher 

dynamic pressure ratio 

- - than the uniform jets; the ratIo ~onuniform/quniform is about 1.7 and 1.5 

for the 90 0 and 600 jets, respectively. The higher q of the nonuniform jet 

results in an increased penetration height and higher trajectory of the 

nonuniform Jet- [Ref. 13). The higher penetration makes the Jet acquire 

characteristics of a jet originating with a hIgher effective R: the Initial 

entrainment and the initial vortex paIr become stronger (because of higher 

penetration), while the blockage is re~uced. These effects should result In 

a pressure field upstream of the jet resem~llng a hlgher "effective" Rease. 

At the same time, the higher trajectory combined with the faster decay rate 

of the nonuniform jet lead to reduced Jet €ffects on the pressure field In 

the region behind the jet and quicker relaxation of the induced pressures 

behind the nozzles. Such an effect can be seen in Fig. 12; the negative 

pressures induced by the nonuniform jets relax faster than those Induced by 

uniform jets having the same nominal velocity. The faster decay of the 

nonuniform jets may be explained by enhanced turbulent mixing occurring in 

nonuniform jets. 

Additionally, it may be argued that the nonuniform jets used in these 

experiments are vlewed by the approaching crossflow as jets having 

effectively higher velocity than the uniform jets. It is the outer, highvelocity portion of ea~h jet that first comes in contact and interaction 

wtth the crOssfro~, and,- as -~uch,- it ~ay playa dominant roJe In 

establishing the initial (i.e., upstream of and near the jet exits) 

flowfield and the pressures induced on the surface. It takes some distance 

that the jet must travel from the nozzle exit before the crossflow enters an 

effective mixing and inter2ction with the inner (originally low-velocity) 

portion of the nonuniform jet. As a consequence of such a development, the 

initial jet/crossflow mixing/interaction which is responsible for the 

pressure field upstream of the front jet may exhibit features characteristic 

of a higher effective R value, such as increased regIons of negative 

pressures and reduced regions of positive pressures. The remaining portion 

of the pressure field may become influenced by the interaction of the 

crossflow with the entire Jet Includl~g its inner core which results in a 

more rapid jet decay and a faster relaxation of the induced pressures behind 

the j~t nozzles. 

*The penetration height also depends on the peripheral-to-core velocity 

ratio. The latter remained nearly constant throughout these experiments. 
. . . 

_"L<- __ ........ ~ 

10 

Because the nonunIform jets induce: Ca) a larger negatlve-pr~ssure 

regIon proJectIng further In the upstream dIrection and/or decayIng faster 

behInd the jet nozzles, and (b) smaller positIve-pressure regIons ahead Of 

each jet, the resultant induced pressure torce haa a more forward locatIon 

than that for a un1form Jet arrangement. Th~s may reduce a nose-up PItchIng 

moment on the alrcrart. 

The pressure field Induced by the tandem confIguratIon or 90 0 jets is 

presented in Fig. 13 for the case of uniform profiles at R-2.2. The data 

obtaIned for the other 90° tandem Jets cases have been Judged to be of less 

accuracy and are not Included. DiscussIon of pressures Induced by tandem 

90 0 jets Is presented In SectIon "Tandem Jets at 60°." 

Side-by-Slde Jets at 60° 

Uniform-VelocIty-Profile Jets 

FIgure 1_ shows the surface pressure tleld Induced by the side-by-side 

InclIned jets (&-60°) having uniform velocity profiles and relatively low 

jet velocIty (R-2.2). The Interaction between the two Jets over a distance 

from X/D--l.S to X/D-3 seems to be relatIvely weak. The pressure 

dIstrIbutIons In front of and behInd each jet (wIth the obvIous exception of 

the region along the longItudinal centerline of the whole configuration) 

display features resembling those of single jets; i.e. approximately 

symmetrical left-to-right, positive dC region (for ~C )+.2) and nearly p p 

symmetrical pressure contours near and behind the nozzles with two downwdrd 

projecting lobes. Between the lobes, In the lee of the jets, the contours 

are pulled back closer to the jet nozzles indicating low velocity (less 

negative ~C ) flow regions. Further Jownstream (around X/D-3), both jets p 

start to interact strongly which is r~flected in a merging of the oressure ~ob~~ near the long~tudl~al eenterline Of the side-by-side arrangement • 

As the parameter R increases from 2.2 to ~, the overall area of the 

surtace influenced by the jets increases strongly (Fig. 15). The negative 

pressure area enclosed by the ~C - .3 line increases approximately 150%, p 

relatively large (at R-2.2) positive pressure regions ahead of the jets, 

enclosed by the ~C -+.1 line reduce about 50% and the pressure center moves 

p 

slightly more downstream fro~ the nozzle exit • .. As the Jet Influence increases (when R changes from 2.2 to 4). so does 

the interaction between the jets. As a result. the left-to-right symmetry 

of the pressure contours near the jet nozzles deteriorates and. except f~r 

the very ~trongly negatlve pressu~e region (~C ,-2.0). most of the pressure p 

lines of the two jets merge and, in a sense, the configuration starts 

behaving as a single jet of combined capacity. In the region between the 

jets, along the centerline or the configuration, the effects of both jets 

superimpose, this results in very low pressures. I.e., high velocities near 

the surface betwe~n the jet nozzles and near downstream. 
--_._-_. --------------

11 

When compared with the 90· jets, the 60· angled jets display the 

following changes: 

(a) The surface area influenced by the jets Is reduced. At R.2.2, the 

surface area enclosed by the line ot ACp·-.3 is about ~OS smaller, at R-4, 

the corresponding area is roughly lOS smaller tor the 600 jets, 

(b) The pressures near the jet nozzles are significantly reduced and become 

strongly negative. From Figs. 6, 7, 1~ and 1~, it can be seen that in the 

lateral direction, the pressures near the 600 jet nozzles are lower thyn 

those near the 90 0 jet nozzles within a radius of 1.5 D and 2.5 D for the 

cases of R-2.2 and 4, respectively, 

(c) The lett-to-right sy~~t~y of the pressure contours near the jet exits 

improves significantly. 

The above changes may be explained by the following effects brought 

about by inclination of the jets (Fig. 16): 

(a) The presence of a horizontal (parallel t~ the surface) component of the 

jet velocity which imparts a strong acceleration to the crossflow near the 

jet boundaries leading to very low pressures. 

(b) A reduction of the vortex pair strength and hence the induced flowfield 

velOCities. The vortex strength reduces with decreasing jet inclination 

angle, e, because it is the crossflow velocity component normal to the jet 

which is mostly responsible for the vortex creation. The reduced vortex 

strength results in a reduced lateral expansion of the surface area 

influenced by the jet even though the smaller penetration of the inclined 

Jet- tends to oppose or moderate this trend. 

(c) A reduction of the "solid-wall" blockage due to i"lclination and smaller 

penetration of the jet, and a possible reduction in air mass entrainment 

rate due to the reduced vortex pair strength. These effects tend to 

contribute to a further decrease in the surface areas influenced by the jet. 

While the combined result of these effects is expected to indicate.a 

. reduoed $urface-area affeeted-By the 60 0 jets (\e~sus 900 Jetsr. the effect 

of the jet inclination e on the magnitude of the resultant pressure force 

may be difficult to predict. as it may represent a delicate balance of two 

opposing trends. The surface area affected by the jet decreases with 

decreasing e while the absolute value of the negative pressures near the 

nozzle i~creases strongly. The net result is expected to depend on factors 

such as the jet exit velocity distribution and swirl and turbulence 

characteristics of the jet. These factors are likely to control the 

behavior and decay rate of the jet and thus the jet/crossflow interaction. 

In our experiments with dual jets, acceleration of the cross flow near 

the nozzles (i.e., effect (a» appears to predominate, and the net negative 

pressure force Is larger (leading to a larger loss in the lift force), for 

the 60 0 Jets, particularly at the higher R value (-4), even though the 

overall surface area i~fluenced by the negative pressures is greater for the 

90 0 jets. 

*The jet penetration is controlled by the vertical component of the jet exit 

veloclty. 

.. -~ 
. . .. 

( , 

.' . .. ' 

12 

.... -.. -------r 

The improved left-to-right symmetry of the pressure contours near the 

Jet exits, as the angle e 1s changed from 90 0 to 60 0 , is a direct 

oonsequence of the reduced outward range or influence or the 600 Jets; their 

negative-pressure region is smaller in general and proJects leas in the 

upstream direction, making the mutual Jet/Jet interference weaker for the 

600 jets. 

Nonuniform Velocity-Profile Jets 

The pressure plots obtained with jets having nonuniform exit velocity 

profiles are shown in Figs. 17 and 18 for the cases of R-2.2 and 4, 

respectively. Comparison of the pressure contours in Figs. 17 and 18 with 

those in Figs. 14 and 15 indicates that the patterns obtained with 

nonuniform and uniform jets are generally similar for the same R. However, 

the negative-pressure region to the side of and behind the jets (and 

consequently tne expected lift loss) is increased for the nonuniform jets. 

The positive-pressure regions ahead of the jets are reduced for the 

nonuniform jets. For R-2.2, the region of nonuniform-Jet induced negative 

pressures, based on the ~Cp--.3 line, is estimated to be about 50% larger 

than that for the uniform jets. The concurrent reduction of the positivepressure regions, based on the ~C -+.1 line, is roughly estimated at about 

p 

30~. For R-4. the corresponding estimates are about 35J increase in the 

negative-pressure region and about 75% reduction in the positive-pressure 

regions. These changes may be explained by similar physical arguments as 

those presented in the section discussing 90 0 jets. 

The pressure contours in Fig. 17 indicate two regions of slightly 

positive pressures downstream of the large negative-pressure region. These 

regions may be indicative of near-surface recirculating or reverse-flow 

' .. zonee b.ehl:R-d ,the jet: ·exhaust-s. •.. ·It. .is J.nteresting that a similar, th,ough 

much weaker, feature may be present in the corresponding case (R-2.2) of the 

uniform jets (see the ~Cp-O lines in Fig. 14). 

The effects of increasing R in the nonuniform jet configuration can be 

seen by comparing Figs. 17 and 18. These effects are quite similar to those 

observed with uniform jets. When R is increased from 2.2 to 4, the negative 

pressure area increases about 130%, somewhat less than for the uniform jets. 

The forward positive-pressure areas decrease about 90%. As R increases. the 

jet velocity component parallel to the surface increases correspondingly 

leading to very high negative ~Cp values, such as -7.0 near the jet exits 

(Fig. 18). 

Figure 19 shows the jet-induced lift loss for the slde-by-side 

configurations. The lift loss has been calculated by integration of the 

pressure data obt~ined for a square area extending from Y/D--2 to 4 and from 

X/D--2 to 4. ThlS area is equal to 24.4 times the jet exit flow area. ihe 

pressures in the noninstrumented corners of this area have been assumed from 

extrapolati0 s. Because the contribution of these pressures to the overall 

net pressure ~orce is, in most case~, relatively small. errors involved In 

these extrapolations should not cause dny significant errors in the lift 

loss evaluation. The lift loss. AL. has been nondlmensionalized b) the 

f , 

f 

I 

I 

\ 

I 

I 

I' 

I , 
, , 

/ 

13 

calculated 11ft due to Jet thrust, TL " The latter was calculated for 

nonuniform Jet from 

where mo - mass flow rate of outer flow 

ml - mass flow I'ate of inner flow 

U

o - averaged velocity of outer flow 

Ul - averaged velocity of inner flow 

The 11ft 10S8 data In Fig. 19 indicate a few important effects. First, 

closely spaced dual jets result In significant lift losses, comparable to or 

greater than t~ose typically reported for the single jets. Second, the 60 0 

angled jets induce considerably larger lift loss than the 90 0 jets. Only a 

part of this increase may be attributed to the reduction of the lift due to 

Inclination of the thrust vector. Host of the increase Is due to very low 

pressures i~duced by the ansled jets. Third, the nonuniform jets used in 

these tests result in lower nondimensional lift lo~~ than the uniform jets 

having appr'oximately the same mass flow rate. The 11ft l"!:!I, AL, produced 

by the nonuniform jets was about 35~ larger than the lift loss due to 

uniform jets. However, this increase was more than offset by a significant 

increase of the jet thrust when compared with the uniform jets; hence a 

decrease in the AL/TL value. It can also be seen that the nonuniform-jet 

data pOints can be brought into "alignment" with the uniform-jet data by 

moving them to the left, i.e., toward higher R values. This supports the 

contention that the nonuniform jets behave similarly to the uniform Jets 

having th~ same mass flow rate but a higher velocity ratio. 

Tandem Jets at 60 0 

.... . . . ~he'pressure'disiributL~ns induced by the tandem jet configuration are 

shown in Figs. 20-23. The distributions are generally characterized by a 

large negative-pressure region to the sides of the jets, a relatively small 

positive-pressure region ahead of the front jet and a small region of 

slightly positive pressures behind the rear nozzle. The upstream portion of 

the pressure contours, up to about X/D-+.5, is essentially determined by the 

front jet alone. The remaining pressure contours result from the combined 

influences of both jets. The rear Jet Is obviously shielded by the front 

one. The resulting flowfleld and surface pressure d~stribution near the 

rear jet are very complex and their details could not be resolved with the 

pressure tap spacing used In these experiments; however, we can Identify a 

few very small, local regions of low pressure/high velocity which may be 

related to local vertex-type flows. Th~ front/rear jet interactlon and the 

interaction between the Jets and the crossflow result In a large projection 

of negative-pressure area to the sides of rear jet. 

The oval-shaped, positive-pressure regions behind the nozzles are 

likely to be associated with recirculatory flows. We may note that the rear 

jet, being strongly shielded by the (ront one, exhausts nearly undeflected 

until it ~e€t5 the deflected front Jet. Consequently, an extended wake flow 

may develop behina the rear jet nozzle, involving reversed flow and strong entrain~er.t proco,ses. 

-- -~ --

• 

... 

I \ I • 

I 

l'"' 
14 

Increasing the parameter R in a tandem jet case has similar overall 

effects on jet-induced surface pressure distributions as those observed in 

the side-by-side case. i.e •• negatlve-pressure reglon increases 

signlficantly and the upstream positive-pressure region decreases. However. 

In contrast to the slde-by-slde case. the negative-pressure region increase 

is mostly due to an expansion in the lateral direction. The approximate 

magn1tudes of these changes (as R changes from 2.2 to 4). based on the 

regions enclosed by the lines 6Cp--.3 and 6Cp-+.' are as follows. First. 

for uniform velocity profile jets, the negative 6Cp region increases about 

80J and the positive 6Cp region reduces about 80J. Second. for flonuniform 

velocity profile jets, the negalive 6Cp region increases about 90J and the 

positive 6Cp region decreases dlmost 90J. The center of the resultant 

pressure force moves somewhat forward with increasing R. 

Comparison of pressure plots for the nonunif?rm jets with those for the 

uniform jets indicates, again, trends similar to those produced by an 

increase in the parameter R. Thus. nonuniform jets generate a larger 

negative 6C

p region and a smaller upstream positive 6Cp region than uniform 

jets of the same mass flow rate and the same R. At R-2.2. the negative 6Cp 

area enclosed by the -.3 line is about 50J larger with nonuniform jets. 

while at R-4. the increase is about 60J. Most of that increase seems to 

occur to the sides of the jets which may Indicate relatively small changes 

in the resulting pitching moment. 

The positive pressure region which develops along the centerlin~ behind 

the rear nozzle appears to be more pronounced for the low R case for both 

uniform and nonuniform jets. It may be recalled here, that for the side-byside jet configuration, a similar feature (rear positive-pressure region) 

wa~ oQserlle9. at .l.o~ ~ c~ses 0TJly: . . .. . ... Comparison of the pressure fields induced by the angled (0-60°) and 

transverse (0-90°) jet exhausts reveals the following tentative observations 

(based on the case of uniform jets with R-2.2). First. the negativepressure region around the 90 0 jets is significantly larger than for the 60 9 

case (see Figs. 6 and 20). Second, the pressures near the sides of the jet 

exits are lower for the 60° jets than for the 90° jets which tends to 

compensate the effect of the reduced negative ~Cp region for the 60° jets. 

Third. when the angle changes from 90° to 60°. the center of the negative 

pressure field moves rearward which leads to an increased nose-up pitching 

moment on the aircraft. Last, the upstream positive ~C region increases 

p 

cO~Sldprably when the jet angle changes from 90° to 60°. This causes a 

change in the pitching moment having the same trend as the main effect 

produced by the negative pressure field changes. 

Comparison of Pressure Fields for Slde-by-Slde and Tandem Jets 

A general comparison of the surface pressure fieldS induced by side-byside and tandem jets indicates some important differences. TandeM jets 

operated with the same e, R and exit velocity profile as the side-by-slde 

I 

! 

t 

, 

t 

f 

I , 

I 

r 

I 

I 

I '
. . . . " 

15 

Jets. 1nduce weaker negat1ve pressure t1eld8, resultIng 1n s1gnltlcantly 

lower 11ft losses. This Is caused maInly by the fact that the closely spac~d rear Jet 1s effectively shIelded by the front one and Is thus 

prevented from InteractIng with the freestream and developing features such 

as a strong vortex pair whIch plays an important role In establIshing 

surface pressure fIeld. 

Another general characteristIc of the tandem jets distInguishing them 

from the slde-by-side Jets are the presence of a poslt1ve-pressure regIon 

in the wake zone and rapId relaxatIon of the negative pressures behind the 

jets. The positive-pressure region is likely to be aSSOCiated with reverse 

flows which may develop in the wake behind the nearly undeflected rear jet. 

Rapid relaxatil)n of the downstream pressures may result from strong jet/jet 

interaction; the ensuing highly intensified turbulent mixing disrupts the 

vortex pair ~f the front jet and contributes to a rapid spread and decay of 

the plume formed from the merged jets. This will be followed by a quick 

relaxation of surface pressures. Both the positive-pressure region and 

rapid relaxation of the negative pressures contribute to ~ decrease in the 

jet-induced lift loss. 

Flowfleld Measurements 

The velocity vectors in the plane of symmetry of the transversely 

injected tandem jets with R-2.2 are shown in Fig. 24. For the uniform 

velocity profile jets, the trajectory of the front jet Is bent sharply by 

the oncoming cross flow while the sheltered rear jet rises almost 

undeflected. The front jet centerline intersects the rear jet at a height 

of about Z/0-1.5. The "combIned-jet" centerline, defined as the locus of 

maximum velocities, penetrates about ~D into Lne freestream. Upward 

orientation of the velocity vectors beneath the plume is indicative of the 

presence of a vortex p~ir. ' .. . - .. . . For the nonuniform jets, the front jet centerline intersects the rear 

jet at a height of about Z/0-2, and the centerline of the "combined jet" 

penetrates about 50 into the freestream. The greater penetration of the 

nonuniform jets can be readily explained by their greater effective dynamic 

pressure. The wake of the nonuniform jets decays faster with downstream 

distance and the velocity vectors below the combined plume are less upward 

oriented. These observations tend to 3uggest a stronger turbulent mixing 

inside the jets and a related weaker vortex pair for the nonuniform jets. 

CONCLUDING REMARKS 

An experimental study has been conducted to determine surface pressure 

distributions on a flat plate model with dual side-by-side and tandem jets 

injected at 90 0 and 60 0 angles with jet-to-crossflow velocity ratios of 2.Z 

and 4. The major objective of the study was to determine the effect of a 

nonuniform jet velocity profile resembling a practical engine case. 

The main conclusions uerlved from the study are as follows: 

1. Nonuniform jet~ with a high-velocity outer annulus and a lowvelocity core induce stronger negative pressure fields than uniform jets 
/ 

, " 

---------------r 

16 l 

with the same mass flow rate. This effect is mostly due to the higher 

average dynamic pressure of the nonuniform jets. 

2. Changing the injection angle from 90· to 60 0 results in a moderate 

(for tandem jets) to significant (for side-by-side jets) increase of the 

induced negative pressures and, hence, in increased lift loss, even though 

the surface area influenced by the jets tends to reduce as the angle 

decreases. 

3. Side-by-side jets "esult 1n significant nondimensional jet-induced 

11ft losses, AL/TL, which are comparable to or greater than the lift losses 

reported for single jets. 

~. Nondlmensional lift losses induced by nonuniform jets are lower 

than 11ft losses due to uniform jets. 

5. Nonuniform jets induce larger nose-up pitching moments than the 

uniform jets with the same A, e and jet configur~ticn. 

6. Closely spaced tande~ jets indu~e considerably lower lift losses 

than side-by-side jets. 

7. Pressure fields induced by tandem jets feature a positive-pressure 

region in the wake flow and a rapid relaxation of the negative pressures 

behind the j~ts. Both these effects contribute to a decrease in the jetinduced lift loss. 

8. For all the configurations tested, the effect of R was the SR~~ ~s 

previously documented in literature. As R is increased (from 2.2 to 4), 

both the surface area influenced by the jets and the resultant negative 

pressure force increase. However, this trend is not expected to continue at 

higher R values. On the basis of physical arguments presented in this paper 

it is suggested that, at least with 90 0 injection, the trend will be 

reversed when R increases above about 8. 

Simple physical explanations are offered for the main trends and 

effects observed in these experiments. The pronounced effects of dual jet 

·oO'nfiguratiol'},. jet, ~njeGtlon. angle and eut velocity profile upon the 

induced aerodynamic loads point to a need for a more systemat1c' 

investigation of the respective effects. In particular, it is recommended 

that experiments are extended over a wider range of injection angle (e • 45° - 105°), higher velocity ratios, and other jet exit velocity profiles. They 

also should include investigation of the effects of swirl and initial jet 

turbulence. 

ACKNOWLEDGEMENTS 

The authors wish to express their sincere gratitude to George Aoyagi 

from NASA Ames who mcde it possible for us to receive the necessary 

instrumentation thus (r~tributlng greatly to our reqearch. He was also most 

helpful in providing us with information and advice concerning selection of 

the jet profiles and pressure measuring techniques. 

.1 

i 

j 

1 

t 

, • 

I 

1 • 

, 

I 

£ ..... 
" 

I 

I 

/ 

/ 

/ 

1. 

2. 

4. 

5. 

6. 

7. 

8. 

.9 .•. 

10. 

11 • 

12. 

17 

REFERENCES 

Volger, R.D., "Surface Pressure Distributions Induced on a Flat Plate 

by a Cold Air Jet Is~u1ng Perpendicularly from the Plate and Normal to 

a Low-Speed Free-Stream Flow," NASA TN 0-1629, 1963. 

Bradbury, L.J.S. and Wood, M.N., "The Stat1c Pressure D1str1but10ns 

Around a C1rcular Jet Exhaust1ng Normally From a Plane Wall Into an 

A1rstream," C.P. No. 822, Brit. A.R.C., 1965. 

Margason, R.J., "Jet-Induced Effects in Transit10n Flight," Conference 

on V/STOL and STOL Aircraft, NASA SP-116, 1966, pp. 177-189. 

Margason, R.J., "Review of Propuls10n-Induced Effects on Aerodynamics 

of Jet/STOL Aircraft," NASA TN 0-5617, 1970. 

Fearn, R.L. and Weston, R.P., "Induced Pressure Distribution of a Jet 

in a Crossflow," NASA TN 0-7916, 1975. 

Vogler, R.D., "Interference Effects of Single and Mult1ple Round or 

Slotted Jets on a VTOL Model in TranSition," NASA TN 0-2380, 1964. 

Fricke, L.B., Wooler, P.T. and Ziegler, H., "A Wind Tunnel 

Investigation of Jets Exhausting Into a Crossflow," AFFDL-TR-70-154, 

Vols. I-IV, U.S. Air Force, December 1970. 

Schetz, J.A., Jakubowski, A.K. and Aoyagi, K., "Surface Pressures on a 

Flat Plate with Dual Jet Configurations," Journal of Aircraft, Vol. 

21, No.7, 1984, pp. 484-490 • 

. p,rkin~, S.C., Jr. and Mendenhall, M.R., "A Study of Real Jet Effects 

on' the Surface Pressu"re D1strlbution Induced by a. Jet in a.CrossOpw .. " 

NASA CR-166150, 1981. 

Kuhlman, J.M., Ousterhout, D.S. and Warcup, R.W., "Experimental 

Investigation of Effect of Jet Decay Rate on Jet-Induced Pressures on 

a Flat Plate," NASA CR-2979, 1978. 

Ziegler, H. and Wooler, P.T., "Analysis of Stratified and Closely 

Spaced Jets Exhausting into a Crossflow," NASA CR-132297, 1973. 

Marchman, J.F., "Wind Tunnel Lab Manual," Dept. of Aerospace and Ocean 

Engineering, Virginia Polytechnic Institute and State University, 

Blacksburg, VA. 

13. Abramovich, G.N., "The Theory of Turbulent Jets," MIT Press, 

Cambridge, MA, 1960. 

. -(

I 

... 
. . . 

----------, ------- -------....-- ~ 

, ' 

.' . . .' 

18 

Test Section s.de walls 

1------- 1.83 m ------.-1 

(6 ft ) 

t.---+ ------- 2.13 m ------....... 

( 7 ft ) 

62.5 em 

(24.610) 

Instumented 

panel . ... ~ ___ ~i--Nozzles 

il FLOW 

Boundary 

Layer trtp 

Fig. 1 Flat Plate Model 

c Eo 

IX)- ,...' ...;= 

~r 

I 

I 

i 

I 

i 

I . 

I I 't-' .. 
.... 

. :

U) 

E 

u 

«r 

U) 

o 

~ 

I 

J 

Test section ceiling 

4 93 em .1 

(194 In dla)1 

19 

Air from 40 m 3/ min blower 

4- Air from 

8.5 m!/min blower 

Screens 

Stream separation 

IOsert 

..... 

Flg. 2 Cross-Sectlonal Vlew of Nozzle Assembly 

I 

i 

I 

. ~ 
". 

/ 

--

----------

+ ++ +++ 

+ ++ +++ 

+ ++ +++ 

+ ++ +++ 

+ + + +++ 

+ ++ + + + 

+ + + + + + + + + + + + 

+++ + + + ++++ ++ 

+ + + + ++ ++ ++ ++ 

+ ++ + + + + + + + + + 

+ ++ + + + ++ ++++ 

++++++ + + ++++ 

+ + + +++++++++++ +++++++++++ 

+++++++++++ +++++++++++ 

+++ 

+++ n:+.t :r+ gt+ +, U it + + + r ++ 

+ + + nh+++dn 

+++ +++++++++++ iihmifii 

++++++ 

+ + + + ++ 

+ + + + + + 

t FLOW 

(0 1 Side - by - Side Configuration 

+++++++ 

+ + +++ + + 

+++++++ 

+++++++ 

...... + +++ + + 

+ + +++ + + 

+++++++++++ 

+++++++++++ 

++++ ++++ 

+++ +++ 

++ ++ 

tt U 

+++ +++ 

++++ ++++ 

+++++++++++ 

+++++++++++ 

+ + + ::UtUnU 

+ + + iU'" eft: 

+ + + ++. ++ 

++ ++ 

+ + + !!+ y +!! 

+ + + ++++ ++++ +++++++++++ 

+ + + +++++++++++ 

+ + + + .,. + 

+ + + + + + 

++++++ 

t FLOW 

++++++ 

+ + + + + + 

++++++ 

+ + + + + + 

++++++ 

+ + + + + + 

++++-1'+ 

+ + + + + + 

++++++ 

+ + + + + + 

+ + + + + + 

++++++ 

(b) Tandem Configuration 

Fig. 3 Plate Pressure Tap Layouts 

20 

/' 

In 

4 

3 

2 

I 

0 

C c c 

I 

t 

• I 

f 

1 

j 

I , 

I , 

I 

i 

! 

. 

I 

i. 

f 
-------..,---~ .... -..... -., 

V 

E 

L 

0 

C 

J 

T 

T 

f 

T 

I 

S 

E 

C 

V 

E . . . -.... . . l 

0 

C 

J 

T 

l 

f 

T 

I 

S 

E 

C 

200 

125 

100 

75 

50 

25 

0 

'I"""'" I"""" 'I" "Y"'t''"i''T'r"""TTT'l~ 

0.0 0.5 1.0 I.S 2.0 2.5 

POSITION INCHES 

Uniform Exit Profile 

200 

175 

150 

125 

100 

75 

SO 

25 

0 

0.0 o.s 1.0 ' 1.5 2.0 2.5 

POSITION INCHES 

Nonuniform exit Profi1e 

Fig. 4a Exit Velocity Profiles of 90° Jets. 

Pltot-Statlc Probe T1P 1.6 mm 

(1/16 in) from Nozzle EXlt 

• 

-----'tJ 

21 

• 
/ 

''\ 

t •• 

---------_ .. _.--.".,.. --..... ------ .~-- ._-_.--------

.' 

200 

V 

E 175~ L 150 

0 

C 125-

I 

T 100 i 

'( 

75l 

F 

T sol 

I 

E 

5 25~ C o I 

0.0 0.5 1.0 1.5 2.0 2.5 

POS Ii I ON INCHES 

Uniform Exit Profile 

200~11--­

____________________ ~L 

V ~ 

E 175-1 

~ 1 c;oJ ... 1 

? 1251 '( 100 

I 75 

N 

so 

F 

P 25 

5 

0-, ~1~"~"~i~"~"~li~i~"~"~i~"~li~"~i~"~"~il~i~"~"~"ni-~~~+ 

0.0 0.5 1.0 1.5 2.0 2.5 

POSITION IN INCHtS 

Nonuniform Exit Profile 

Fig. 4b Exit Velocity Profiles of 60° Jets. 

Pltot-Statlc Probe T1P 1.6 mm 

(1/16 1n) from Nozzle Exit 

22 f 

f 

J 

J 

I 

• I 

i 

I I 

~ 
... 

---------~,~ .. _ ...... , ..... ----- --_.-._-

. , . 

I· • 

1.01~------------------------~ 

Z 0.5 

i 

R r' 2.2 

O.O~-------------~a 

0.0 o.s 

U/U. 

1.0 

1.O~------------------------~d 

R = 4 

. . ... ,," .. 

z 

6" O.S 

0.0 r--------------~~ 

0.0 O.s 

U/U 00 

Fig. 5 Boundary Layer Profiles, 90° Jets 

1.0 

23 

. .' 

\. 

\ 
5 

4 

3 

2 

X/D 

0 ... . , ' . 

-I 

-2 

-3 

~~ ~~ .. ............ ----- ,.,. ... ~--"'---- . 

24 

" , 

I 

I 

I 

I 

I 

I 

, 

I 

I 

I 

I 

I 

-21 . I 

-.1 

+15 

-2 -I 0 

Y/O 

Flg 6 Ineuced Pressure Dlstrlbutlon (. Cp)' 

Side-by-S1de Jets, Unlform EXlt Proflle, 

e = 90°, R ~ 2.2 

.-

"'" I 

t 

J 

-.1 ~ r I 

~ 

I 

• i 

t 

I • 

\ ~ 

· \ I 

j \ 

\ • 

· \ l' 

, \ I 

\ l , 

, 

, i 

• 

I 

I f 

I , 

• i 

, 

t 

; 

~ 

I 

L · , 

+05 

2 3 
. -

X/D 

... 

25 

5~------~----~------~------~------~-----, 

4 

3 

0-.7 

o 

-I 

-.1 

-.2 

, 

, 

" 

-.1 

, 

\ 

, 

\ 

-2L--------~~-----~-----------L---------J---------~----~ -3 -2 -I 0 2 3 

Y/O 

F19 7 Induced Pressure Dlstrlbutlon (: C

p) 

Slde-by-Slde Jets. UnlfOrJ'} EXlt Proflle. 

(i = 90<'. R = 4 

r 
26 

5~----~~----~~----~------~~----~~----~ 

4 

3 

2 

X/O 

I 

-... 

-2~-------~------~----~~----~~------~----~ 

-~ -2 -I 0 2 3 

Y/O 

Fig. 8 Induced Pressure Dlstribution (6Cp): 

Side-by-Side Jets, Nonuniform Exit Profile, 6 = 90°, R = 2.2 

r 

i 

I 

I 

J ~ j 

I 

I 

. ' 

• 

I 
- - --

.( 

27 

5 

r o _ 

-.1 

4 . 

3 

2 

X/D 

_2L-______ L-______ rv--~ L-______ ~ ______ _L __ ~ __ ~ ______ ~ 

-3 

Fig. 9 

-2 -I o 

Y/O 

Induced Pressure Distributlon (~Cp): 

2 

Slde-by-Side Jets, Nonuniform Exit Profile, e = 90°, R = 4 

3 

" 1.1 11 

I I 

, ~ 

.. 

, 

... 

t 

I 

J 

I l 

j 

i 

I • 

.. 
Cross flow 

'/ r" 

v "' 

// 

'" 

:/ .... Jet centerline 

. ( mox velocity) 

/ 

;' 

x 

Fig. 10 Schematic View of a Jet Exiting at e = 900 into a Crossflow 

......... - ... 

.......... 

~ 

" 

\-

\ 

, 

N 

CIC) 

~ \- . \( 
x/o 

' .. .- .... 

. .' 

/ 

4 

3 

2 

o 

-I 

29 

+05 

\ 

\ 

\ 

_2L-____ -J ______ ~ ______ ~ ______ ~ ______ L_ ____ ~ 

-3 -2 -I o 

y/O 

2 

Flg. 11 Effect of EXlt Veloclty Proflle on 

Induced Pressure Dlstrlbutlon (; Cp) 

for Slde-by-Slde Jets, e = 90°, R = 2 2' 

Unlform EXlt Proflle ---------------- Nonunlform [Xlt Proflle 

3 

" l 
/ 

/ X/D 

. 

. 

/ 

30 

5~----~r-----~-------r------.-------r------' 

4 

3 

2 

-I 

-2L---~~L-----~------~--------~--~--~----~ 

-3 -2 -I 0 2 3 

Fig. 12 

Y/O 

Effect of Exit Veloclty Proflle on Induced 

Pressure Olstrlbutlon (~ C

p) for 

Slde-ry-Slde Jets, A = 90 0 • R = 4: 

Unlform EXlt Proflle 

Nonunlform EXlt Proflle 

I 

J 

" 

.' . 

,.~ 

.. 

... 
, 

/ 

l 

, , 

/ 

. 

\ 

31 

5 \: 

\ \ 

, \ 

,) 0.0 

4 

-.1 

:3 

2 

X/O 

o 

-I 

-2L--------L------~--------~------~--------~------~ 

-3 -2 -I o 

Y/O 

Fig. 13 Induced Pressure Distribution C~Cp): 

2 

Tandem Jets, Uniform Exit Profile, e = 90°, R = 2.2 

3 

I 

I 

.. '. 

<Ii 

, 

i 

I 

I I . 

.... 
· ...... . 

, / 

I 

I ' 

/' \ .-: ,- . 

32 

5~------T-------~------~------r-------~------' 

c \' \' - , 

I,l 

,', 

, 

I' \ , , I ,_~ 

.... ~o.o 0.0 

, , , 

4 

3 / 

/ \ 

/ \ 

/ \-.1 

/ -.2' 2 \ / \ / \ X/O I \ 

\ 

.' . .. Q 

-I 

-2~------~~L---~-------L-------L--~~~------~ 

-3 -2 -I o 

Y/O 

Fig. 14 Induced Pressure Dlstribution (llCp): 

2 

Side-by-Side Jets, Uniform EXlt Profile, e = 60°, R = 2.2 

3 

/ 

, 

~ 

I 

I 
/ /' 

, '. 

, \.~-- - -------

33 

5~----~------~------~~--~~----~----~ \J.05 I 

i • 4 

: . . . . 

, 

" / 

-' f 

~ I 

X/O I I 

, 

I 

\ 

\ 

\ 

",' 0\ 

-I 

/ 

/ 

I 

I 

I 

I 

I 

I 

, 

I 

I 

,,5 

\ 

\ 

\ 

\ 

\ 

, 

-2~----~~----~~----~-------L------~------~ 

-3 -2 -I o 

Y/O 

Fig, 15 Induced Pressure Distribution (ACp): 

2 

Side-by-Side Jets, Uniform Exit Profile, e • 60°, R = 4 

3 

"\!-
Crossflow 

~---___ -. I 

"'\ 

x 

, 

---. 

\ 

\ 

\ 

\ 

Fig. 16 Schematic View of a Jet Exiting at 0 • 60° into a Crossflow 

....... '-

, , 

;> 

o 

o 

" 

------------.:... .:~ 

\0) 

l>" 

.. (" ---'-..... ---..~~.'~ ...... ~01_~ 

'\ 

\ 

-------

-- -'-

.. 

/" 
.\t} 

35 

"- , 

"-, 

"- 5 

0.0 

/ 4 

3 -.1 ~ 

" ,,-.2 , 

. -~ \ . \ \ 

2 \ \ - 5\ \ \ \ \ \ X/O \ \ \ 

\ \ \ 

\ \ \ 

.. .. .. -.... 

o 

-I 

-2L------L--~--L------L------L-~---L----~3 

-3 -2 -I 0 2 

Y/O 

Fig. 17 Induced Pressure Distribution (ACp): 

Side-by-Side Je~s, Nonuniform Exit Profile, e = 60°, R s 2.2 
\ \ 

... 

36 

• 

-

5~----~------~------~----~------------~ 

4 

3 

2 

X/O 

.... 

0 

-I 

/ 

/ 

/ / / / / / I / I I I 

-2 -I o 

Y/O 

Fig. 18 Induced Pressure Distribution (t.cp): 

,5 

-7' " , . \ \ 

\-1. \ \ 

\ \ 

-1.5 \ \ 

\ \ 

I ' 

2 3 

Side-by-Side Jets, Nonunitorm Exit Profl1e, e = 60°, R = 4 

\ 

\ 

, 

I 

I 

I 

I I, , , I 

I 1 

I I 

I , , ... .. 

• 

\ 

I ~ 
I 

i 

J 

I 

, 

I " - I 

I 

. " 

6L 

" TL """ 

. . . 

, 

\ -----

37 

0 

-.1 

-.2 

-.3 

900 

-.4 

-.S 

-.6 

-.7 

-.8 

.. ." . 

-1.1 

.1 .2 R=4 .3 .4 R"'2.2. 5 

l/R 

Fig. 19 Nondimensional Jet-Induced Lift Loss for S1de-by-Side Jets· 

Two Nozzle Dlameter Spaclng between Nozzles. 

... 

.. 

.. ..... 
X/D 

---.-.--

-- -------------------------------

38 

5~------r-----~~----~------~------·~------~ 

4 

3 

2 

o 

-I 

// 

/ -.1/ 

I 

I 

--'--

0.0 _-----_~"'_ -- ... 

"""-"""-

0.0 """-

-2~------~------~------~----~~------~----~ 

-3 -2 -I o 

Y/O 

Fig. 20 Induced Pressure Distribution (~Cp): 

2 

Tandem Jets, Uniform Exit Profile. e ~ 60°. R a 2.2 

3 

J. 

r 

I 

I 

I 

I 

I 

I 

. 

~ 

I 

I 

I ... 

~ 
XIO 

~, 

> • I 

39 

5~------~------T-------~------~------~------

4 

3 

2 -.5 -ie 

-I~ 

-2~ 

··0 

-I 

0.0 

-2~-------~------~-------~------~-------~--------~ 

-3 -2 -I o 

Y/O 

Fig. 21 Induced Pressure Distribution (ACp): 

2 

Tandem Jets, Uniform Exit Profile, e ~ 60°, R a 4 

3 

• 
/ 

/ 

/ 

/ 

I 

! 

-- X/D 

.. . . .. 

~ ., - tI' 

I 

I 

" 

40 

5~------r-----~~----~----~~------~----~ 

4 

I 

I 

I -.2, 3 

I 

2 

'0 

-.I 

-I 

,,"" 

/ 

--, 

I 

I 

/ " 

"...-

",,-

/ 

-'1M.. 

-2~ 

-If\ -2m 

-.2 

-2~------~-------~-------~1-------~------~------~ -3 -2 -I 0 2 3 

Y/D 

fig. 22 Induced Pressure Distribution (llCp): 

Tandem Jets. Nonuniform Exit Profile. e R 60°. R • 2.2 

I 

r , 
/ .. -""-- / 

X/O 

, ," 

I 

/ 

41 

5--------~------~------~----~------~------~ 

4 

I 

21 

I 

\ 

\ 

1 

-I 

-2L-------L------J------~------~------~----~ 

-3 -2 -I o 

Y/O 

fig. 23 Induced Pressure Distribution (ACp): 

2 

Tandem Jets, Nonuniform Exit Profile, e • 60°, R K 4 

3 

\, 

I '\ 

k 
, ,- I J ! , 

/ , 

~ .--" 

---- ~""'«>l:i'''fo''''''j'~~ ,'..,., ... ~-. -~ -, , .... . _.. .... \. - ... \ ... "... "'-.\.. --

. Uniform Exit Profile 

on 

42 

6 

-

--

-

- f 

-

-

-

-

-

--

--

-- -- --

-- - - - -

- -- - - --

---

---

-

-

-

-

- I 

-

-

- - -

--

-- 4 - - - - - - - 

- - - - - - - - - - - - ::: - .. ... ~ .- - - - i .... - .. .. // - - - ~ - .. .. Z/D - - .. .,6 .. , :: { - - ... ~ ... , ~ - - ... '1 I ~ ~ I - -

, ~ 

-

- ~ ~ 2 - ... I ... ... ~ ~ ~ - ~ ::: - ~ .... ... ~ ". .... 

? ~ ~ '" .... 

r 

-

- ~ 

., .... , 

.. .. 

--

-- 0 rI I 

I 

! 

i 

/ 

.. ~ 

Nonuniform Exit Pro1 .e ! 

t 

6 ... 

-

-

- ... 

- ... 

-

- ... 

-

-

-

-

-

1 

-

- - - ... 

- ... 

-

-

- 

... - ... .... - ... ... - ... - ~ - - ... - - .... - ... ... - - .... :;: .... ~ .. 4 - ... ~ ... ". , - ... " .,. " ~ 

/' 

-

- ... ~ " , ... ... ... ~ ~ Z , ~ .. /' Z/D - .,. 

(" 

~ ::: . 

-

- /. .. f. ; '- ... f ~ /. 

- ... ~ .~ • - ..- ~ I - ~ ~ .". I i - ~ ..-

2 

- ?' ~ .... - '" .... ... ~ '" ..-

~ , ~ " 

-'" 

-- ~,.,J ... ... r ~ ... - , , .. - ,-- 0 rI 

o 2 4 6 8 

X/D 

Fig. 24 Velocity Vector Plots: 

Tandem Jets. e a 90°. R • 2.( 
J 1 , I /1 

I • , 

.' / 

I. / // I 

I 

I 

- --I I 

. , .' i 

I 

I 

-I 

// 

I 

; I 

j/ 

I 

I , 

/ 

I 

I ' 

/ 

I 

.' 

I 

. ' 

, , 

! , ,,' /~ I ,. ./ , , , ,,- ! - / 

43 

APPENDIX A 

COMPARISON OF MACHINE AND HAND-MADE PRESSURE CONTOURS 

Figures A1-A3 compare pressure contours traced out by computer with 

contours obtained by hand plott1ng. The computer plots were generated by 

the Cal COmp General Purpose Contouring Programs. Spacing of the grid 

polnts at which the pressure magnitudes and gradients were established, was 

varied between 0.1 D and 0.5 D. The plot~ generated with grid spacing of 

0.25 D were judged to be the most adequate, and they are shown in Figs. AlA3. The hand-made contours were traced out on the computer generated 

layouts of the numerical pressure data. 

From Figs. Al-A3 it can be seen that computer tracing worked QuIte well 

In regions where the density of Input data points (compare Fig. 3) was 

sufficiently lyrge to handle local pressure gradients. Near the inner 

(i.e., nozzle exits) and outer boundaries, as well as In ~egions containing 

rapid pressure changes concentrated in small areas, the computer plotting 

tailed to produce satisfactory contours. While the machine plots were 

judged to be of inadequate accuracy for handling all the data of these 

experiments, it is expected that sufficient accuracy can be obtained 1n 

future applications provided that the two following aonditions can be met: 

1. The surface area covered by the Input data must be Increased 

considerably; such area should be at least 60 times larger than the exit 

nozzle area. ThIs would allow to plot accurately the negatIve-pressure 

contours down to, at least, ACp values of -.2. 

2. The density of pressure input data near the nozzle exits should be 

increased; the spacIng between the pressure taps next to the nozzles should 

be as small as possible (3-4 mm (0.12 - 0.16 In.)) • . ". .. . .. -. . .. ... 

Ii, / 

I.' --/. 

/ 

'
/ . 

.J 

'1' 

\ 

I. 

I 

f 

\ I 

I' , , '/ • 

I 

I 

, 

I . \/ 

~ \ 

--{ 

I 

I 

/ 

I 

.1 

l 

I 

I 

~ 

/ 

/ 

/ / 

~,"/' /, , -

,f 

I 

I 

t ~ 

I 

c 

X/D 

.' . 

.~ - / / -I 

44 

5~------~------~------~------~~------~------~ 

, ,"-

--- ... --~ 

4 

3 

2 

-I 

\ 

\ 

-.2 

\ 

\ 

\ - 3 \ " , \ \ \ , 

\ " '...... " ...... "", 

-2~------L-------~------~------~--~--~------~ 

-3 

Fig. Al 

-2 -I o 

Y/O 

2 3 

----- MACHINE PLOT 

- HAND PLOT 

Comparison of Computer- and Hand-Made Pressure Contours: 

Side-by-Side Jets, Nonuniform Exit Profile, e = 90°, R = 4 

./ 

~ , 

f. '" 

1 

i 

I 

I 

I 

I 

L 
I 

I 

I 

" , I 

/ 

1/ . / 

I 

I 

I 

I 

7; 

I 

/ 

/ 

/ 

I 

I ., . 

I 

I • 

,I 

/ 

/ 

. 

t / \ 

\ " ,/ D'S:1)'t":spa, • Tr!!6 

45 

4 

3 

2 

X/D 

-I 

-2~------~------~------~~------~------~------~ 

-3 -2 -\ o 

Y/O 

2 3 

----- MACHINE PLOT 

- HAND PLOT 

Fig. A2 Comparison of Computer- and Hand-Made Pressure Contours: 

Side-by-Slde Jets, Nonuniform EXlt Profile, e = 60°, R = 4 

I ~ ! 

I 

t 

~. 
I 

/ 

/ ' 

/ 

. 

.. 1,/ , 

J .. 

/ 

. ... . ... 

,', , 

I 

I 

I 

/ 

/ 

; 

/ 

J 

/ .. 

X/D 

, ' 

"I \ 1/ ;' #,./' 

/{j" " 

.,., , '" M I _ ... - t 

y / ( / / ~ / I 

-- , 

-... --------r 

46 

4 

-I 

-2~------~------~------~--~~~------~----~ 

-3 -2 -I o 2 ,3 

Y/D ----- MACHINE PLOT 

- HAND PLOT 

Fig. A3 Comparison of Computer- and Hand-Made Pressure Contours: 

Tandem Jets, Nonuniform Exit Profile, e = 60°, R = 4 

1 

, . 

• 

, 

I 

I 

I 
.: 

(/ 

I \ t'~ 

J" J ,'/', j\ /1/ 

I 

I /, 

! , 

" 

1-_- ----

",-

" 
End of Document