CFD Dynamic Pressure and Thrust Characteristics of Cold Jets Discharging From Several Exhaust...

7/27/2019 CFD Dynamic Pressure and Thrust Characteristics of Cold Jets Discharging From Several Exhaust Designed for VTO

1/81

I

N A S A T N D - 2 2 6 3

_.

I C PRESSURE A N D T H R U S T

OF COLD JETS

R V T O L D O W N W A S H S U P PR E S SI O N

C . C .

Higgins and T.

W.

Wuinwright

No. NASw-462 by

ROEING COMPANY

Washington

A E R O N A U T I C S A N D SPA CE A D M I N I S T R A T I O N W A S H I N G T O N , D .

C

A P R I L

1 9 6 4


2/81

TECH

LIBRARY

KAFB, NM

0354982

DYNAMIC PRESSURE AND THRUST CHARACTERISTICS O F C OL D JETS

DIS CHARGING F R O M S E VE R AL E XHAUS T NO Z Z L E S

DESIGNED FOR V TO L DOWNWASH SUPPRESSION

B y C. C. Hig g in s and

T.

W. Wa in wr ig ht

P r e p a r e d u n d e r C o n t r a c t No. N AS w- 46 1 by

THE

BOEING COMPANY

Renton , Wash ing ton

This report w a s reproduced photographically

from

copy supplied by the contractor.

NATIONAL AERONAUTICS AND SP AC E ADMINISTRATION

For sale by t h e O f f i c e of T e c h n i c a l

Services,

D e p a r t m e n t

of

C o m m e r c e ,

Wash ing ton , D.C . 20230 - - Price $2.00


3/81

DYNAMIC PRESSURE AND THRUST CHARACTERISTICS

O F COLD JE TS DISCHARGING FROM SEVERAL EXHAUST NOZZLES

DESIGNED FOR VTOL DOWNWASH SUPPRESSION

By C. C. Higgins and T. W. Wain wright

SUMMARY

Several exhaust nozzle mode ls

we r e

tested on

a

stat ic r i g using cold

air

flow to find t he effect of exit design on thrust and

jet

wake dynamic pre ss ur e for

use in VTOL downwash suppression.

Data f ro m both free jet and ground plane

tests ar e

presented to define dynamic p re ss ur e along the jet wake centerline and

along the ground surface. Results show that th ree ba si c nozzle design fact ors

can be very

effective

in causing rapid dynamic pr es su re decay in the

jet

wake

with small

effect

on nozzle velocity coefficient.

comp ared throughout the mixing region f or each nozzle and are shown to be

s i mi l a r .

Dynamic pr es su re profi les are

INTRODUCTION

Ground impingement of the downwash fro m any VTOL air cr af t can produce

operational problems of varying degree, depending on the type of landing site

being used and disc-loading of the l i f t sys tem.

wash problem is a function of the maximum dynamic pressure in the

jet

wake at

the ground surface,

a

gen era l tre nd of designing fo r low-disc-loading l i f t devices

on many cu rre nt VTOL ai rc ra ft has resulted . However, high-speed airpla ne

mission req uirem ents have resulted in aircraft designs incorporating sepa rate

lift jet engines o r combined l i f t and cr ui se turbo-fan engines.

On

jet

VTOL

air-

craft

currently in use, operations have been restricted in some manner to mini-

mize ground damage.

reduction of exposure t im e by mean s of sh or t ground ro ll

o r

l i f t

nozzle rotation

at take-off.

Since the sev er it y of t he down-

Such restr ict ion s have included using hardened sites

o r

A significant amount of re se ar ch has been accomplished by se ve ral inves-

tigators in attempts to understand the action of

a

jet impinging on the ground and

in

finding the limi ts of eros ion re si sta nc e that various s ur fa ces have to

jet


4/81

impingement,

as

described in references 1 to 3.

to

develop various coverings, coatings, and st ru ct ur es that improve the erosio n

chara cterist ics of ground surfac es.

shown to be effective, but, in mo st cases, logistic proble ms and installation re-

quirements make

it

desirable to minimize o r el iminate the need for ground prep-

aration. This can

be

done only by reduction of the ground impingement dynamic

pre ssu res . The apparently conflicting requirements for

jet

engines in VTOL

aircraft and low ground dynam ic p re s s u re s have led to this stu dy of exhaust noz-

zle design fac tor s which, by increasi ng the rate of mixing with ambient

a i r ,

will

alleviate the ground impingement problem.

Also, there have been efforts

Many of the surface treatments have been

Thi s investigation involved the testi ng of twelve nozzle configurations, in-

cluding: cir cu la r designs which attempted to vary upst rea m turbulence; rectan-

gular slot designs for a study of exit per ime ter /are a rat io and exit w a l l angle;

and secto red configurations fo r the effect of exit area subdivision.

z les were tes ted on a stat ic, cold a i r flow ri g at the Airplane Division of Th e

Boeing Company, Renton, Washington. Me asu rem ent s of th ru st and

jet

wake

dynamic pressure were made for each nozzle a t pre ss ure ra t ios ranging f rom

1.4

o

2 . 4 .

Free

je t wake surveys

w e r e

made by traversing the

jet

a t several

downstream locations, and

a

ground plane was u sed to obtain dynamic pres su re s

radially along the surface

after

jet impingement.

These noz-

The simil ari ty of the nozzles used in this pro gra m to those used in pre-

vious sound suppre ssion work is apparent, and the objective

is

basically the

sa me , namely, to increase the rate of jet mix ing, although the effe ctive ness of

a sound suppr ess or nozzle

is

primarily due to changes in the directivity and

frequency of the noise, ref ere nce s 4 and 5.

Thus sound suppression ch aracte r-

istics of

a

nozzle may o r may not be rela ted t o the reduction of dynamic pres-

s u r e in the jet wake, which is the goal of a VTOL downwash suppression nozzle.

T h is r e s e a r c h

w a s

spo nso red by the National Aero nauti cs and Space Ad-

ministration through the Office of Gra nts and Rese arc h Cont racts under contrac t

NASW

46

1.

SY

MBO

LS

R

cF

V

C

e

aspect rat i o, D2/Area o r length/width

m as s flow coefficient, actual m a ss flow /ideal m as s flow

effective velocity coefficient, effective exit velocity/ideal

exit velocity.

Effective velocity = (th rus t /ma ss fl0w)actual

dia me ter of nozzle exit, inches

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I

X

* *5qz

X

max

Y

25s-

Y

.L

max

h

n

p t

p t

+z

n

P

P

di am ete r of a circ ular nozzle with exit area equal t o tha t of

a

non-circular nozzle, inches

length of rect angu lar exit planfo rm, inches

width of rect ang ular exit planfor m, inches

radi al distanc e fro m cente r of ground plane, inches

ax es of a right hand coordinate sy ste m with the Z axis in the

directi on of flow. Also designa tes distances along each

re-

spective axis from center of nozzle exit , inches

designation of an ax is i nter med iate between se gme nts of noz-

z les

N o .

11 and N o . 12

distance fro m co re o r apparent core to any point in the

mixing region, measured parallel to the

X

axis, inches

(ref.

:

figure 12)

dis tance f rom core o r apparent core to reference contour

at twenty-five per ce nt dynamic pr es su re , inches

( ref .

figure 12)

distance from c or e o r apparent core ' ' to any point i n the

mixing region, mea sur ed parallel to the

Y

axis ? inches

( ref .

:

figure 12)

distance from core or apparent core ' ' to reference contour

at twenty-five per cent dynamic pre ss ur e, inches ( ref .

:

figure 12)

height above the ground plane, inches

number of exit segments

a tmospher ic pressure , lbs /sq f t

total o r s tagnation press ure , lbs /sq f t

total o r stagnation pre ss ure at the nozzle exit , lbs/sq f t

total o r stagnation pre ss ur e a t any specified point in the

jet

wake: lbs/sq

f t

total o r stagnation pres sur e a t any specified point on, o r

adjacent to the ground plane, Ibs/sq

f t

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6/81

compressible dynamic pre ssu re , p t

-

po, lbs /sq ft

q

q n

compressible dynamic pre ssu re

at

the nozzle exit, ptn - po,

lbs /sq

f t

compressible dynamic pre ss ure

at

any speci fied point in the

jet wake, ptz

-

po, lbs/sq ft

maximum dynamic pr ess ure measured at any specified trans-

m a x

ve rs e plane perpendicular to the Z axis, pt

sq f t

- Po, 1bS/

Zmax

compre ssible dynamic pr es su re at any specified point on, o r

adjac ent to, the ground plane, pt

maximum compressible dynamic pr ess ure measured on, o r

adjacent to, the ground plane a t specified distances of the

ground plane fro m the nozzle, pt

gmax

99

- po, lb s/s q ft

g

q

9max

-

pol Ibs/sq ft

total o r stagnation temperatur e, OF

n

t

B

total o r stagnation temperatur e at nozzle exit, O F

nozzle wall divergence angle, re fe rr ed to the longitudinal

axi s of the nozzle, deg ree s

e

angle subtended by

a

nozzle sector , degrees

APPARATUS

AND

PROCEDURE

Models

The nozzle models used in this program a re described in figures 1 to

3 .

Nine basic convergent nozzle designs w e r e tested including a c i rcu la r ,

f i v e

rec-

tangular-slot, and thr ee multiple-segment nozzles. The cir cu la r nozzle had

provisions fo r incorporating turbulence-generating ins er ts consis ting of a sand-

paper lining, vortex gen era tor s, and concentric rings. The rectangular slot

nozzles provided variation s in exit aspect ratio and wall angle.

segme nt nozzles had the exit

area

divided equally into

2 , 4 ,

o r 1 2 sec tors .

The multiple-

All nozzles w e r e designed to have the s am e physical exit ar ea

as

that of

the three inch diameter cir cular nozzle.

to approximately the sa me cross-sec tiona l area distribution from entrance to

exit.

The circu lar nozzles varied somewhat from

the non-circular nozzles because

a

straight throat section

w a s

required for the

turbulence inser ts. Because the resulting profile of nozzles No. 7. 8 , and 9

when viewed from the side resembles that of the G r e e k lettei-A , these nozzles

have been ter med delta nozzles.

'I

In addition, the nozzl es we re designed

This is shown in figure 4.

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7/81

The models w ere fabricated from mild steel and fiberglass to be consist-

ent with the cold

air test

requirement .

Nozzle A i r Rig

The arra ngem ent of the

test

facility which

w a s

used for th is program

is

shown schematically in figure

5 ,

with further details shown photographically in

f igure

6 .

Additional details of the instrumentation a r e shown

in

figure 7.

The nozzle models w er e installed on

a

bellmouth adapter

at

the end of the

24

inch inside-diameter plenum cha mb er.

int eri or of the plenum cha mb er reduced the effective plenum s iz e to

20

inches

inside diameter.

Internal

baffles

and

a

fine mes h scr ee n in the plenum cha mber

ins ure d uniform distributi on of the f l o w at the entr ance of t he bellmouth section.

The plenum

w a s

hung from

a

super-structure by means of four flexures which

minimized re sis tan ce to fore and aft motion. Air w a s introduc ed into the plenun

by way of

a

flexible bellows joint arrangem ent. Nozzle thr ust w a s meas ured by

a st ra in gaged thrust ring installed between the plenum as sem bly and the rigidly

supported

air

supply pipe.

Acoustical lining insta lled on the

Airflow w a s me as ur ed with an ASME long rad ius flow nozzle up st re am of

the load cell and flow r at e w a s controlle d by

two

valves, one ups tre am and one

down strea m of the flow nozzle. The dual valve arr ang em ent maintained

a

con-

sta nt Mach numb er through the flow nozzle for

all

data points and nozzle si zes .

Filtered air fo r the nozzle tests was obtained fro m

a

laboratory supply system

at

approxim ately 70F with

a

dew point of -40F o r less.

Pr es su re measurements in the

jet

wake

we r e

obtained with a t ravers ing

prob e mounted downs tre am of the plenum. Operation of thi s prob e

w a s

remote-

ly controlled to vertical,

lateral,

o r longitudinal positions with re sp ec t to the

nozzles . Pr es su re readings w e r e transmitted through transducers to the re-

cording equipment.

A

56

inch diam ete r ground plane

w a s

installed on rails dow nst rea m of the

A

five-tube total pre ssu re r ake which measured pres sur es a long a

The pres -

plenum.

radial t rav ers e above the surf ace w a s attached to the ground plane.

su re tubes covered a height

of

. 05 to

1 . 0

inches above the ground plane.

ground plane could be located at distances up to

20

feet fr om the nozzle.

The

All data obtained fr om nozzle testing w a s automatically recorded on

IBM

punch c ar d equipment which mad e

it

possible to de cr ea se data reduction tim e

to approximately one day.

In

addition,

a

Moseley

x-y

plot ter was used to recor d

jet wake pre ss ur e fo r on-line evaluation of nozzle performance.

5


8/81

I

Data Accuracy

Calibrations of the static ri g instrumentation showed that pre ssu re

measurements w e r e acc ura te within

f

0.5 per cent in

all

axes, thrust

scatter

band width

w a s

2.0 per cent, and

air

flow sc at te r band

w a s

0.7

per cent.

Al-

though the test data sca tte r band appears large , repetition of the te st

runs

s ix

or mo re t imes provided a grouping of the data fr om which mea n values of

thr ust and airflow w e r e determined. It w a s found that these mean values w e r e

within f

0.5

pe r cent of the values obtained on another ext reme ly sensitive and

pre cis e nozzle calibration r ig normally accepted as a stand ard within The

Boeing Company.

The velocity profile of the

air

entering the nozzle models w a s closely

checked with

a

rake incorporating ten total pr es su re probes located in the ten-

ter

of five equal areas. Distortion w a s found to be negligible for more than 90

pe r cent of the nozzle inlet diamete r.

Plots of the jet wake tr av er se s indicated that minor profile distortion oc-

cu rr ed , with the amount of distortion dependent upon the dynamic pr es su re

gradients and the level

of

pr es su re s being measured. Attempts to eliminate

this distortion w e r e not successful. During the dynamic pr es su re tra ver ses , it

w a s

apparent that intense, lar ge sc ale turbulence w a s often encountered. N o

corrections were made in the measurements f or the effects of turbulence, con-

sequently the absolute value of dynamic pressure may be somewhat in doubt for

specific points.

On occasion, random variations of f

0.05

nozzle exit dynamic

pre ssu re w ere noted; however, most data appeared to fall within a band f 0 .01

nozzle exit dynamic pre ssu re.

Because of uncertaintie s assoc iated with static pr ess ur e measurements in

an intensely turbulent str ea m,

all

dynamic pre ss ur e measurements

w e r e

ob-

tained

as

a differentia1 pr es su re between the indicated probe total pr es su re and

atmospheric pre ssu re. Presentation of the data in this form introduced effects

of

compressibility , but these

were

minimized by the low nozzle pressure ratio

used

for

most

of

the tests.

RESULTS

Nozzle Performance Evaluation

Effective velocity and m a s s flow coefficients de termi ned fo r

all

nozzles

are presented in figure 8. Nozzle pr es su re ratio w a s var ied f rom 1.4 to

2.4,

and all tests

w e r e

conducted with laboratory supply

air

of 60 to 80F. The data

shown

w e r e

obtained by visually fairing r es ul ts

of six

or mo re individual tests

on each nozzle ove r the range of pre ss ur e ra t ios indicated.

6


9/81

Effective velocity co efficients we re based on the rat io of effective jet

velocity, determined from mea sured thrust and ma ss flow, to isentropic jet

velocity resulting from the nozzle pr es su re ratio and tempera ture.

coefficients wer e base d on the ratio of meas ured m as s flow to theoretical ma ss

flow determined by the nozzle are a, pr es su re ratio, and temp eratu re. When

nozzle exit

area

is

cor rec tly selected to compensate for variation of ma ss flow

coefficients

,

nozzle thru st efficiency is specified solely by effective velocity

coefficient; consequently, effective velocity coefficient provides the bes t mea ns

of comparing the per for man ce of vari ous nozzle designs.

Mass flow

The two fa ct or s which we re found to influence nozzle per form ance signifi-

cantly included 1) nternal roughness o r flow obstructions ne ar the nozzle

thro at sectio n (nozzles no. 2 and

3) ,

and (2) dive rgen ce of the nozz le wall s

(nozzles no. 7 8, and

9).

Both fact or s w er e found to be dependent upon nozzle

pr es su re ra t io , with the losse s minimized at the higher nozzle pres sur e ra t ios .

A s

may be se en fro m the resu lts fo r nozzles no.

1, 2 , 3 ,

and

4,

hrust losses

we re la rg es t fo r obstruction s placed in the high velocity regions of the nozzle.

Despite the la rg e amount of blockage intr oduced by the turbulence ring s with

configuration no.

4, hru st l os se s wer e nominal because of the low velocities a t

that location. The data clear ly indicate that both effective velocity and m as s

flow coefficients de cr ea se with increasing divergence angle f or the delta noz-

zl es , but the effect of incr easin g aspec t rati o

is

le ss well defined.

Com par iso n of the effective velocity and m as s flow coefficien ts for noz-

zles no.

1, 5,

6, 10, and

11

indicates t hat variatio n of nozzle exit planform had

only sm al l effect upon the se coefficients. Considerati on of the re su lt s of nozzle

no. 12, however, sugg ests that the effective velocity coefficient may be adv ers e-

ly affected by changes of planform in which the nozzle exit perimeter is greatly

incr eased ove r that of

a

ci rc ul ar nozzle. The data do not perm it precise defini-

tion of this tre nd , no r will

the

data perm it isolation

of

the effects of other design

variables (such a s the number and radii of internal cor ne rs , ar ea progression

changes , sur fac e roughness ,

etc.

).

The variation of mass flow coefficient

shows even l e ss dependence on nozzle p er im et er than does the effective velocity

coefficient; consequently, it may be concluded fr om these data that friction

los ses associated with la rge nozzle wetted ar ea s may be a secondary factor in

determining nozzle performance.

F r e e Jet Wake Surveys

Surveys of the dynamic pressures in the free jet wake we re completed fo r

all nozzles operating at a pre s su r e r a t io of 1. 5. The maxi mum values of dy-

namic pressure

at

each survey s ta tion

a re

presented

as

a

function of distance

from the nozzle exit in figure

9.

These data a t

a

nozzle pr ess ur e ra t io of 1 .5

show that substantial reductions of dynamic pr es su re in the fr ee jet wake may

be achieved by each of th re e methods, namely:

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10/81

1)

distribution of the nozzle exit

area

in the shape of a long rectan-

gular slot; i . e.

,

incre ased a spect rat io of the nozzle exit plan-

for m. (nozzle no.

6

2)

introduction of lateral components into the flow prior to discharge

from the nozzle,

as

is

accomplished with the delta nozzles.

(nozzles no. 7 8, and 9)

subdivision of the nozzle into sev er al e lem ent s (nozzles no. 10,

11, and 12).

3)

The data of fi gure 9a indicate al so that dynamic p re ss ur e degradation of

the free jet wake

is

influenced only to a sma ll de gree by disturbances o r turbu-

lence introduced into the st re am pr io r to discharg e fr om the nozzle. Two pos-

sible explanations for these res ult s may be considered:

1)

the sc al e and intensity of the turbulence gen era ted in the

nozzle we re of suc h

a

sm all magnitude and per sis ted for such

a

sho rt t ime that the

jet

was essentially free of turbulence at

the nozzle exit.

2) turbulence of the sca le , intensity, and orientation that

w a s

generated in the nozzle does not play a significant pa rt in the

jet wake mixing proc ess .

Of the two possible explanations offered, the lat te r app ea rs to be mor e plaus-

ible.

Com par iso n of the resu lt s of nozzles no. 1 and no. 5, figur es 9a and 9b,

shows that changes of the nozzle exit planform fr om a cir cul ar to a square shape

had a very mi nor effect upon the dynamic degradation ch ara ct er is ti cs of the

wake. Increasing the nozzle exit aspect ratio from 1 . 0 to 6 .0 , nozzles no. 5

and 6 , figure 9b, significantly changed the dynamic pre ss ur e degradation cha r-

acteri stics of the rectangular nozzles, but increasing the aspect ratio fro m 2 . 0

to 5. 0, nozzles no. 7 and 9, figure 9c , fo r delta nozzles with a

30

divergence

angle made a much sm all er change in degradation character istics . In this cas e,

the effect of divergen ce angle dominates a ll othe r vari abl es in determining dy-

namic p re ssu re degradation.

An interesting effect associate d with multiple element nozzles is shown

in figur e 9d. Comp ariso n of the re su lt s of nozzles no.

1 0 ,

11, and 12 shows

a

cr os si ng of the degradation curv es at distances of ten equivalent nozzle diam-

e t e r s

o r

mor e; these resul ts

are

believed to be caused by

a

me rg in g of the

small je t segments in to a very much la rg er jet wake. The resulting degradation

rat e of the larg e jet is much les s than that of the sm al le r je ts , consequently,

the degradation curves exhibit a plateau in which very lit tle reduction of max-

imum dynamic pre ss ur es occur. Note that this effect is much le ss pronounced

8


11/81

with nozzle no.

11 than with nozzle no.

12; this is a reflection of the f e w e r num-

b e r of seg ment s used in nozzle no. 11.

During free jet wake surve ys of c ir cu la r nozzle no.

1 , it w a s noted that a

distinct instability in the shape and degradation chara cte ris tic s of the wake oc-

cur red at pr es su re ratios of approximately 2.1 o r greater. At the higher noz-

zle press ure ratio s, the jet wake appeared to divide into

a

two-lobe pattern

which would rot ate slowly around the longitudinal axis of t he nozzle.

havior w a s apparently assoc iated with the appea rance of shock wave formations

at

the nozzle exit, and it

w a s

noted that any obstruction immediately adjacent to

the nozzle e xit would change the occ ur re nc e and shape of the lobed jet wake pat-

tern .

instability character istic s.

)

This instability, although completely reproducible

with the cir cu la r nozzle no. 1, was n eve r o bse rve d with any of th e other noz-

zles.

This be-

(F or example, placing a hand nea r the nozzle would alter the jet wake

Bec aus e of the i nstability noted above, jet wake survey s w e r e completed

for

a

range of nozzle pr es su re ratios from

1.1

to

2 . 4

with circ ul ar nozzle no.

1,

as

shown in figure

loa.

In addition to the usual

jet

wake surveys

at

selected

nozzle pr es sur e ra t ios , a variable pre ssu re survey w a s conducted with the

probe located

at

the point in the jet wake where maximum values had been pre-

viously me asure d f o r the various surve y stat ions; this data i s shown also in

figure

loa.

Becau se ins tabil itie s of t he type noted above we re not observe d with the

other nozzles, only limited jet wake surve ys

at

nozzle pr es sur e ra t ios other

than 1.5 w e r e taken. These resul ts are prese nted in figure 10b through 10d.

J e t wake contour maps of equal dynamic pr es su re levels

w e r e

constructed

for various nozzles operating at

a

pr es su re ra tio of 1 . 5 by cross-plotting data

from trave rse s of the

free

jet wake

at

vario us s tatio ns downstream of the noz-

zle; these contour maps are shown in figure 11.

length of the dynamic pr es su re contours appear s to be associated with increased

width o r dispersion

of

the jet wake. The contour maps show that non-circular

jet wakes apparently mix in such

a

manner that the jet wake approaches a cir-

cular cross -sect ion a t so m e point well downstream of the nozzle.

ter ist ic may be seen in the plot fo r the rectangular nozzle, AR =

6,

f ig ur e l l c ,

and the delta nozzl e, AR

=

5, f l = 5 , fi gure l l d . The str ong influence of delta

nozzle divergence angle is appar ent in the plot fo r nozzle no. 9 , AR = 5, B =

30 ,

figure

l l e :

the jet wake does not approach sym me try within the range f or

which data a r e available.

In general, reduction of the

This charac-

It should be noted he re tha t the edge of the je t designated by the symb ol

q z / %

3

exi sts only

as

a

threshold sensitivity

for

the equipment used in the

wake sur vey s. Although the boundaries determ ined in this man ner are some-

what fictitious, they provide

a

basis of comparison of

jet

spreading charact er-

is tics.

While not determined preci sely, the threshold sensitivity of the equip-

ment appeared to be on the or de r of 0 . 0 0 7 5 psi, which is 0.1'2 of dynamic

9


12/81

pr es su re a t nozzle exit fo r the tes t condition shown. In considering the above

profile maps, as

w e l l

as the si mili tude plots which follow,

it

should

be

noted

that individual me as ur em en ts in turbulent flow may va ry widely with time . Be-

ca us e of r ando m variation of both instantaneous and mea n values with tim e,

so me latitude in interpretation of the re sul ts obtained a t specific points is pos-

sible.

In general, all data wer e interpret ed in

a

man ner which would provide

conservative values of dynamic pr es su re degradation.

The resu lts obtained from the

free jet

wake survey s wer e analyzed in a

manner s i mi lar to that of references 6 through 10 to de ter mi ne the regio ns of

the jet where similitude of the mixing pro ces ses existed. If similitude exists,

velocity profiles a t various distances f rom the nozzle can

be

made congruent

by suit abl e choice of velocity and width scale fac tor s, and the analysis of the

mixing region w i l l be considerably simplified.

shown by means of nu mero us experim ental and theoretical studies during the

past f if ty yea rs (references

6

through 10) that the wake of c ir cu la r je ts

is

char-

act eri zed by velocity di stributions which are approximately

similar

at large

distances fr om the nozzle.

As

a result of this similitude, the development of

a

c i rcu la r

jet

may

be

des cri bed by specifying the va riat ion of velocity along the

longitudinal axis of the jet, together with a typical la te ra l dimension related to

the spreading of the jet. Previ ous investigators have succe ssful ly extended

analyses of this type to the jet wake of two-dimensional sl ot nozzles, and it

w a s

believed that the r esu lts of the cur re nt tes ts p resen ted a n opportunity to inves-

tigate whether similitude exists f or a varie ty of nozzle s hapes with three-

dimensional jet wakes . Although velocity ra ti os a r e normally used in simila r-

ity studies, the cur ren t analyses were conducted using the data as available in

te rm s of dynamic pr ess ur e ra t ios .

Previ ous investigators have

Establishment of similitude in this m anner re qu ir es knowledge of 1) the

tr an sv er se dista nce from the jet axi s to the initiation of the active mixing

region;

i . e . ,

distance to the outer extremity of the co re o r apparent coreTf

region, and

(2) location of a consistent reference point somewhere in the mix-

ing region. The refer enc e point commonly chosen is the point where the veloc-

ity

is

one-half that of the maximum velocity meas ure d during each trave rse :

the corresponding reference point in the present

tests

was selected as the point

where dynamic pre ss ure w a s twenty-five percent of the maximum value meas-

ured during each probe tra ve rs e acr os s the jet. Figur e 12 illustr ates the geom-

etr y used to specify eac h of the above quantities, together with

a

plot illustrating

the variation of the cor e, o r apparent core,

nozzles.

width fo r various non-circular

The core is defined to be that region in the ce nt er of the

jet

wake in which

the velocity o r dynamic pre ss ure

is

undiminished f ro m that a t the nozzle exit ,

i .

e . ,

that area in which no mixing has occur red. The apparent core is de-

fined to be that region ex clusive of the c or e in which the velocity o r dynamic

pressure

is

essentially constant and equal in value to the maximum value which

may be measured at any given axial distance fro m the nozzle. The values of

velocity or dynamic pr es su re in the apparent core are always less than those

10


13/81

in the co re region.

prog ress ion of mixing along two o r mo re coordinate axe s toward the cen ter of

the jet.

The apparent core provides a mea ns of desc ribi ng the

Th e location of the twenty-five per cen t ref er en ce contou rs of dynamic

press ure , together with the dynamic pre ss ur e s imilar i ty profiles

,

are

shown

f o r

all

nozzles in figure 13.

Fr om these plots , i t

is

apparent that a high degree

of two-dimensional sim ilit ude doe s ex is t in the mixing region of ea ch of the noz-

zles.

It is

also appare nt fr om the twenty-five percent refer ence contours that

these contours w e r e often quite non-linear with re spe ct to distance from the

nozzle exit . Great est non-linearities w e r e noted for the delta nozzles and the

segmente d nozzles, which

is

an indication that the high rates of dynamic

pressure degradation

w e r e

obtained fro m the three-dimensional asp ect s of these

nozzle designs.

It

should be noted that similitude does not appear to be pre-

ser ved in regions where mergin g of two

o r

m o r e jets occur; i .e .

,

near the axis

of the twelve-segment nozzle, figu re 13j.

The resu lts shown in figure 13 thus indicate that mixing pro ces ses in

non-circular no zzles may be considered s im il ar in the sen se that the non-

dimensionalized dynamic pr es su re distribution

of

the mixing regions for all

nozzles may be approxim ated by

a

single curv e. However, the utility of this

finding

is

virtually negated by the non-linear cha rac ter ist ics of the apparent

core region and the twenty-five percent dynamic pr es su re referenc e contours.

Fur the r study of methods to pre dic t the boundary of the apparent core and the

twenty-five percent dynamic pr es su re re fere nce contour w i l l

be

necessary in

or de r to properly define three-dimensional jet wake chara cter istic s.

Other information related to the mixing process es may also be derived

fro m the twenty-five percent refer ence contours.

directly related to the sprea d of these ref eren ce contours, and

it

is apparent

that

jet

spreading does not occur uniformly along the various coordinate axes.

This is shown in figure 13d, 13e,

13f, and 13g. It is readily apparent that the

je t wakes of nozzle no.

6

figu re 13d , and nozzle no.

8,

figure 13f, approach

symm etry a t so me point downstream of the nozzle, while the

jet

wakes of noz-

zle no. 7, figure 13e , an d nozzle no. 9 , figure 13g, do not approach symme try

within the distanc es dow nstream of the nozzle for which data are available.

Thes e resu lts with nozzles no.

7

and no. 9 again demonstrate the strong influ-

ence of lar ge nozzle dive rgence an gles upon jet wake sprea ding and degradation

charac te r s ics

.

The spr ea d of the jet wake i s

The data shown f o r nozzle no.

10, figure 13h, nozzle no. 11, figure 13i,

and nozzle no. 12, fig ure 13j,

illustrate some of the variations of jet wake

spre adin g and degradation which may

be

encountered with multiple el emen t noz-

zles . In these plots, the

jet

wake f rom a single sector of the various nozzles is

analyzed in the sam e manner

as

w a s done with the prec edin g nine nozz les. How-

eve r, the unsymmetrical shape of the jet wake led to

an

analysis

of

the inner and

ou te r portion of the

jet

separately (the te rm s inner and outer

a re

related to

the longitudinal a xi s of t he nozzl e,

i. e . , that pa rt of the pie-shaped je t wake he-

l l


14/81

tween the longitudinal axis of the nozzle and the point of maximum dynamic

pressure was te rm ed the inner region while the remai ning truncated se ct or of

the jet w a k e w a s ter med the outer region of the wake).

region of the jet showed

a

distinctly non-linear mixing cha rac ter ist ic which is

assoc iated with the merging of the jets near the longitudinal axis of the nozzle.

The disappearance of the twenty-five per cen t refer enc e contour

is

an indication

that the cent er of the wake for the comp lete nozzle had merged into one region

with all dynamic pr es su re s gre at er than twenty-five perce nt of the maximum

dynamic pre ss ur e which existed at that distance fr om the nozzle. Fr om figures

13h,

13i, and 13j, it may be seen that merging of the je ts oc curre d mor e rapid-

ly as the number of nozzle segments became lar ger .

It

is al so significant that

the spre ad of the twenty-five perce nt re fer enc e conto urs fo r the outer mixing

region became less

as

the number of nozzle segm ents becam e large r. In this

respect, the spreading characteristics of a nozzle with a la rg e number of seg-

ments may approach the spreading charact erist ics of

a

circular nozzle.

In parti cular , the inner

Ground Plane Surv eys

Surveys of the dynamic pr es su re over the ground plane were obtained with

a

t raversing, f ive-element , to ta l pre ss ure rake. Static pre ss ure taps w e r e also

positioned flush with the ground plane s urf ace at five radial locations, figure

7 .

The maximum dynamic pre ss ur es measu red adjacent to the ground plane

are

shown in figure

14,

together with the stagnation pr es su re s se nsed by the pressu re

tap at the cen te r of th e ground plane.

Becau se of the limite d number of ra dia l st ati ons , the location and magni-

tude of maximum dynamic pr es su re adjacent to the ground plane

were

not

identified. However, stagnation pr es su re mea sur ed

at

the ground plane provides

a dir ect me as ur e of the maximum possible value of dynamic pr es su re which may

exist o ver the ground plane.

Nozzle pres sur e ra t io

w a s

found to have a very minor effect upon dynamic

pre ssu re degradation, fig ure 14a.

observed in the free je t surveys w a s confirmed by a corresponding reduction in

the stagnation o r dynamic pr es su re s mea sured on o r above the ground plane,

figures

14a

to 14m. Data for the segmented nozzles i ndicate that the maximum

dynamic pr es su re along the ground plane is repres ented by the c enterline stagna-

tion pr es su re only

at

Z/De gre ate r than 1 0 . At the cl os er ground plane locations

maximum stagnation pre ss ure occurs a t som e radial distance from the center.

The reduction in dynamic pre ss ur es previously

The distribution of dynamic pres su re s above the ground is presented in

figures 15 and 16. Figure

15

again

illustrates

the smal l effect of nozzle pres -

su re ratio upon the dynamic pr es su re s at the ground sur fac e, while figure 16

shows the variation of dynamic pres su re distribution above the ground plane for

various nozzles at a pr es sur e r a t io of

1.5 .

It is apparent fro m the se plots that

dynamic pr es su re distributions above the ground plane fo r non-circular nozzles

departed substantially from the profiles associated with conventional circular

nozzles.

12


15/81

The plots of figu re 16 show the development of dynamic pr es su re profiles

fo r various axial and radia l d istances fro m the nozzle and ground plane.

apparent that the combined effects of free st re am mixing and boundary la yer

growth contribute to a rapid degradation of dynamic pr es su re s in

a

radial direc-

tion from the point

of jet

wake impingement

on

the ground plane.

nozzles, highest dynamic pr es su re s in the radial flow ove r the ground plane

w e r e

found at heights of 0.05 nozzle diam eter o r less above the su rfa ce of the

ground plane.

However, fo r non-circular nozzles

,

the highest dynamic pres-

sures in the rad ial flow ov er the ground w e r e found a t heig hts of 0 .07 nozzle

diameter o r higher above the ground plane. The data fo r nozzle no. 1 2 , f igure

16m: when compa red with that of nozzle no. 1 , fi gur e 12a, show part icula rly

well changes of distr ibution of dynamic pr es s ur e over the ground plane that may

be anticipated as the res ult of inc reas ed mixing prio r to impingement with the

ground surfa ce.

may als o exhibit diff eren ces of sh ape and maxi mum valu es, depending upon the

coordinate axis surveyed.

These character is t ics

are

particularly evident in the

plots for nozzle no. 6, figu re 16f, nozzle no. 7 , figu re 16g, nozzle no. 8, fig-

ure lGh, nozzle no.

9 ,

figure 16i, nozzle no.

1 0 ,

figur e 16j, and nozzle no. 11,

figure 16k.

impingement with the ground sur fac e will be re flect ed in

a

much thic ker flow

profile ove r the ground surfac e.

minimize erosion of loosely held ground surfaces.

It is

F o r c i r cu la r

The profiles of dynamic pr es su re for non-circular nozzles

The figures als o indicate that coalescence of the jets p rio r to

A profile of this type may be desirable to

DISCUSSION

In ord er to pres ent mo re concisely som e of the res ult s of these tes ts ,

five nozzles

w e r e

selected f or comparison of the thrust and

f ree

je t wake dy-

namic pr es su re degradat ion character is t ics , f igure

17 .

Effective thru st coeffi-

cient shows

a

sm all variation with nozzle pr es su re ratio, while dynamic pres-

su re degradation varies principally as a function of axial distance from the

nozzle exit to the plane of me asur eme nt. Both effective thr ust coefficient and

dynamic pr es su re degradation show la rge variation with nozzle configuration;

however, the changes related to dynamic pr es su re degradation a r e much la r ger

than a r e the changes in effective th rus t coefficient.

Fo r example ; a t a nozzle

press ure ra t io of 1 . 5 and a distance of four dia mete rs fro m the nozzle exit , the

twelve seg ment nozzle

w a s

found to reduce dynamic pr es su re s in the

jet

wake

by m or e than eighty per cen t of that of the cir cu la r nozzle, while effective veloc-

ity coefficient

w a s

redu ced by only th re e and one-half perc ent.

In the case of

the delta nozzle ( f i = 5 , A R = 5 .0) a t a nozzle pre ss ur e ratio of 1.5 and a dis-

tance of four di am ete rs fro m the nozzle exit,

the results show a fifty percent

reduction in dynamic p re ss ur e with le ss than one perce nt reduction in effective

velocity coefficient.

It may b e noted that the delta nozzle

( @

= 30 ,

AR = 5 )

was

also

very effective in achieving dynamic pr es s ur e degradation of mo re than 80 X :

however, the effective velocity coefficient w a s reduced by approximately seven

percent with this nozzle design.

13


16/81

Fur the r analyse s of the interrelatio nship of dynamic pr es su re degrada-

tion and thr ust

are

shown in figur e

18.

Using the difference between the

free

je t dynamic pre ss ur e of

a

ci rc ul ar nozzle and that of ot her nozzles as a cri te-

rion, it may

be

see n that maximum reductions of dynamic pr es su re relative to

that of the circ ul ar nozzle

a re

achieved in the range of four to eight nozzle di-

am et er s from the nozzle exit . Significantly, the gre ate st reductions

a re

achieved at the correspondingly cl ose r locati ons with resp ec t to the nozzle exit.

Figure

18

also indicates that

a

large reduction of dynamic pr es su re s may be

achieved with smal l thrust losses . Fo r

two

nozzles tested, no.

6

and no.

11,

no thrust losse s were incurred despi te the fact that dynamic pressures w e r e

greatly reduced fr om that of the ci rc ul ar nozzle. Within certa in limi ts, it may

be concluded that dynamic pressure degradation

of

the

free jet

wake i s virtually

independent of nozzle t hru st pe rform ance.

press ure degradation, a reduction of nozzle thr us t is indicated by the data.

F o r the la rg es t values of dynamic

Corre lati on of free

jet

wake dynamic pressure degradation characteristics

as a function of nozzle ex it peri me te r i s shown in figur e 19.

pre ssu re degradation appea rs to increa se with increasing nozzle exit perim eter,

i t i s clear that o ther factors a lso exe rt

a

very large influence upon dynamic

pre ssu re degradation. This effect is shown mo st cl ear ly in the data for delta

nozzles no.

8

and 9 of figu re 19. Both nozzle no.

8

and no. 9 had esse ntial ly

equal values of exi t pe ri me te r, but the nozzle divergence angle for nozzle no. 8

was 5 , compared with

a

correspondin g dive rgence an gle of

30

for nozzle no. 9.

The curves w e r e faired through data points of nozzles no. 7 and no. 9 because

both nozzles had the s am e divergence angle of

30 .

Although dynamic

During analy sis of the data, it

w a s

found that the cu rv es of figur e 19a

w e r e

not completely defined by the rectangular nozzles tested in the present program.

Additional data, shown by the flagged symbol s in figu re 12 a, were obtained from

reference

4

by computing je t wake dynamic pr es su re s, then extrapolating the

results to a nozzle p re ss ur e ratio of

1 . 5

to be con siste nt with the other nozzle

data.

Replotting the data of f igur e 19a, with as pe ct ra ti o of th e nozzle exit

as

a

prim ary var iable, produced the resu lts shown in figure 20.

from reference

4 w e r e

utilized again as shown by the flagged symbol s in figur e

20. It

is

clear from f igure 20 that increasing aspect ra t i o resul ts in lower

dynamic pres sur es in the exhaust jet wake: however, the change of dynamic

pressure as a function of aspec t ra tio becomes prog ress ively less

as

aspect

ra t io is increased.

Extrapolated data

By combining data fr om fi gure s 1 9 and 20,

it

was found that the effect of

delta nozzle divergence angle could be repre sen ted by the c urv es shown in figu re

21.

It is apparent from t hese c urves that increasing nozzle divergence angle

provides corresponding lower dynamic pre ss ur es in the exhaust jet w a k e with

progressively sm al le r benefits obtained

as

nozzle divergence angle incr eases .

14


17/81

A comparison of maximum dynamic pr es su re s in the f re e jet wake with the

maximum dynamic pres sur es o r s tagnat ion press ure s m easured on

o r

adjacent

to the ground plane

is

shown in figure

22.

that the ground plane did not substantially change the free jet mixing character-

istics.

those nozzles with very rapid

jet

wake degradation cha rac ter ist ics wer e least

affected by the pres en ce of the ground plane.

From these resu l t s ,

it is apparent

Although the e ffec t of t he ground plane w a s s imi l a r fo r all nozzles tested,

CONCLUDING REMARKS

Several sm all -sc ale exhaust nozzle models have been evaluated with re -

spe ct to nozzle perf orma nce and jet wake degradation chara cteri stics .

Effec-

tive velocity and m as s flow coefficients w e r e found to be re lated prim arily to

internal passage details i.e.

,

roughness and

w a l l

divergence), while jet wake

degradation cha rac ter ist ics wer e related to nozzle

exit

planform, divergence of

the flow

at

the nozzle exit, and subdivision of the jet wake into sm al le r ele-

ments.

The pres ent res ults indicate that additional dynamic pr es su re degrada-

tion may be achiev ed by nozzle designs which combine all thr ee of these facto rs,

(i.

e. ,

nozzle exit planform, flow divergence, and subdivision s of the wake).

Although thrust lo ss es do not appe ar to be directly relat ed to dynamic degrada-

tion characteristics,

it

app ear s that nozzle designs fo r maximum dynamic

pressure degradation w i l l be somewhat lar ger ,

w i l l

have m ore wetted su rface

area, and w i l l be m or e susceptible to internal flow lo sse s than ci rcu lar nozzles.

Nozzles which incorporate flow divergence

(as

exemplified by the de lta nozzles)

w i l l be penalized a ls o by the cos ine

l a w

of vectored thrust components.

The pre sen t results indicate that a high degre e of sim ilari ty exis ts

throughout the

free jet

mixing region of ea ch nozzle; however, str ong three -

dimensional effects make prediction of the boundaries and refer ence contours

of the mixing region difficult.

The close correlation between fr ee jet wake ch ara cte ris tic s and the dy-

nami c pr es su re imposed upon the ground plane has been demonstrated, and it

is

evident that any significant reduction of dynamic p re ss ur es in the free

jet

wake w i l l produce a corresponding reduction of the dynamic pr es su re s imposed

upon the ground surface.

Airplane Division, The Boeing

Company

Renton, Washington

October

25,

1963

15


18/81

REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

9.

10,

Kuhn, Richard

E.

: An Investigation to De ter mi ne Conditions Under Which

Downwash fr om VTOL Aircra ft Will S tar t Surface Erosion Fr om Various

Type s of Te rr ai n. NASA TN D-56, Sept emb er 1959.

Morse, A. : VTOL Bownwash Impingemen t Study, Sum ma ry Report.

TREC Technical Report 61-37, Hill er Air cra ft Corp ., August 1960.

Grotz, C. A.

:

Simulated VTOL Exhaust Impingement on Ground Surfaces.

D2-6791, Th e Boeing Company, Jun e 1960.

Laurence,

James

C . , and Benninghaff, Je an M. : Turbulence Measure-

ments in Multiple Interfering Air Jets.

NACA TN 4029, Dec ember 1957.

Coles, Willard D. :

Jet

Engine Exhaust N o i s e F r o m Slot Nozzles. NASA

TN

D-60,

Septemb er 1959.

Prandtl, L. : The Mechanics

of

Viscous Fluids. (Included in Durand's

Aerodynamic Theory, Volume 111, Division

G

1935, Julius Spring er,

Berlin.

)

Schlichting, H . : Boundary La yer The ory, McGraw-Hill,

N e w

York, 1955.

Townsend, A. A. : The Struc ture of Turbulent She ar Flow.

Cambridge

University

Press,

London, 1956.

Johannesen,

N .

H. : Fu rt he r R esul ts on the Mixing of

Free

Axially Sym-

metr ica l

Jets

of Mach Num ber 1.4 0. A.R.C .

20,

281,

F.

M. 2817,

N. 88. Univ ersi ty of Manch est er, May 1959.

Kolpin, Ma rc A. : Flow in the Mixing Region

of a Jet.

ASRL TR 92-3,

Mas sach uset ts Institute of Technologv. Ju ne 1962.

16


19/81

A.

B.

C.

D.

PARALLEL SECTION (ADAPTER FOR INSERTS)

SMOOTH

I N S E R T

(USED WITH NOZZLE CONFIGURATION NO.

1 )

SANDPAPER

I N S E R T

(USED

WITH

N O ZZLE C O N FI G U R ATI O N N O .

2)

VORTEX GENERATOR I N S E R T (USED WITH NOZZLE CONFIGURATION NO. 3)

E.

CONVERGENT SECTION (USED

WITH

N O ZZLE C O N FI G U R ATIO N S N O . 1

THROUGH NO.

4)

F.

NOTE:

C O N FI G U R ATI O N N O .

4

CONSISTED OF N O ZZLE C O N FI G U R ATI O N N O .

1

TURBULENCE RINGS (USED WITH NOZZLE CONFIGURATION NO. 4 )

WITH

THE ADDITION OF T H E TURBULENCE

RINGS

UPSTREAM

OF

THE CON-

VERGENT SECTION

Figure 1.- Cir cular nozzle configurations.

17


20/81

N O .

7

N O .

IO

N O .

5

RECTANGULAR NOZZLES

NO. 8

DELTA NOZZLES

N O . 1 1

SEGMENTED NOZZLES

NO.

6

N O .

9

NO.

12

Figure

2.

- Non-circular nozzle configurations.

18


21/81

(X AXIS)

- (Z AXIS)-

-

-@

(V

AXIS)

I

DIAMETER

I

I N S E R T 4

IN S E R T IN S E R T

2

I N S E R T

3

(a) CIRCULAR NOZZLE AND I N SER TS

Figure 3. - Nozzle configurations.


22/81

-

5

6

7

8

9

+

2.66 2.66

0

6.51 1.08

30 3.76 1.88

5"

5.94

1.19

30 5.94 1.19

(X AXIS)

I

I

- L

- - w

NOZZLE

NUMBER

I

f l

I

L I w

b

RECTANGULAR SLOT NOZZLES

AXIS)

Figure 3. - Continued.


23/81

8.0

t

DIAMETER

I

10

1 1

12

I --+Z AXIS)

2

36

4 18

12 6

AXIS)

'

\NOZZLE

I SEGMENT

(X

AXIS)

NOZZLE I NUMBER OF

NUMBER SEGMENTS

(c) MULTIPLE SEGMENT NOZZLES

Figure

3.

-

Concluded.


24/81

BELLMOUTH INSTRUMENTATION TRANSITION NOZ ZLE

12 SECTION

=j=

SECTION

MA XIM UM ENVELOPE,

NON-CIRCULAR NOZZLES

CIRCULAR NOZZLES

4

CIRCULAR NOZZLE

I N S E R T LOC A TI ON

(N OZZLE 1, 2, 8.3)

TURBULENCE

RINGS

(NOZZLE NO.

4)

I

I

-

I

I

I

I

I

7

CIRCULAR NOZZLES

(EXCLUDING

I N S E R T S )

-

NON-CIRCULAR NOZZLES

-

I

I

I

I

I

I

1

L

6

28 32

40

4

DISTANCE FROM PLE NUM - INCHES

Figure 4.

-

Typical nozzle cross-sectional area and Mach number progression.

22


25/81

Figure

5.

- Schematic of test rig and facilities.


26/81

T E S T RIG PLENU M CHAMBER

GROUND PLANE WITH

TOTAL PRESSURE RAKE

THRUST MEASURING RING

WITH STRAIN GAGES

Figure 6.-

Photographs

of test

rig.

24


27/81

GROUND

(a) JET WAKE TRAVERSING PROBE

PLEN UM CHAMBER

24.75

OD;

20 ID

TRAVER SING JET

I

(b ) GROUND PLANE PRESSURE

INSTRUMENTATION

WAKE

PROBE

z - - \P=____

MOVEABLE GR OU N

PLANE

(56

IN. DI A

c )

TEST RIG

ARRANGEMENT

Figure

7.

- Schematic of test r ig and instrumentation.

25


28/81

U

0)

-

U

3 .92

9

Lu

2

L

.88

U

Lu

U

L

3

0

N O Z Z L E PRESSURE RA TIO,

p, /p,

n

(a) CIRCUL AR NOZZ L E S

Figure

8 . -

Variation of effective velocity and mass flow coefficients with nozzle pressure ratio.

26


29/81

U

u

I-

2

U

E

>.

e

U

9

w

w

c

>

L

t:

LL

LL

1

.oo

.96

.92

1.00

.96

VU

I-

5 .92

2

U

E

.a4

3 .E8

9

U

v)

.

O

1

.o

I

I-

7

-

-l-=-

--

I

RECTANGUL AR NOZZL ES

- - - - - - -

-----

DEL TA NOZZL E S

1 . 2 1.4

I i i i i i i.6

1 .E 2.0 2.2 2.4

N O ZZ L E PRESSURE RA TIO , ptn/p,

(b)

R E C TA N G U L A R A N D D EL TA N O Z Z L E S


27


30/81

P)

U

I

5

8

L

LLL

>

c

U

9

W

>

W

I

2

E

U

U

1 .oo

LL

U

- 9 6

c

L

E

.92

3

.88

LL

vr

.84

.80

1 .o 1.2 1.4 1

N O Z Z L E P RESSU RE R A T I O ,

ptn/p,

c )

S E G M E N T E D N O Z Z L E S

I

1

I

I

I

I

I

2.2 2.4

Figure 8. - Concluded.

28


31/81

(a) CIRCULAR NOZZLE

I I I I

.o

.8

.6

.4

C

= -

\

. L

E

0-

C

@

5

2

c

W

v)

W

L

2 1.01

2

Z

>

n

.8

.6

. 4

. 2

0

0

I r r I

7

I

I

f

I

r

5

10

+

I

T r

T

NOZ Z L E CONF I GURAT I ON

SMOOTH THROAT

SANDPAPER

VORTEX GENERATORS

TURBULENCE RINGS

P+ /P,

= ' - 5

I I I I I I

I

I7-l

I I

(b) RECTANGULAR NOZ ZLE

NOZ Z L E CONF I GURAT I ON

0 .

R = l

6 = 6

45 50

AXIAL DISTANCE FROM NOZZLE EXIT/EQUIVALENT CIRCULAR NOZZLE DIAMETER,

Z/De

Figure 9.-

Jet wake dynamic pressure degradation.

29


32/81

(c) DELTA NOZZLES

1 .

C

0-

x

0

E

0-

(d) SEGMENTED NOZ ZLES

AXIAL DISTANCE

FROM

NO ZZ LE EXIT/EQUIVALENT CIRCULAR NO ZZ LE DIAMETER, Z/D e

Figure 9.-

Concluded.

30

......._.

.

.

...

..


33/81

IO 15

20 25 30 35

40

45

d

. . -

NOZ Z L E

P, /Po

n

__

1 2.36

1

2 . 36

1 2.01

2.01

2.01

1.50

1

1

~

1.271

1.097

AXIAL DISTANCE

FROM

NO ZZ LE EXIT/EQUIVALENT CIRCULAR NO ZZ LE DIAMETER , Z/D,

1.2 1.4 1.6

1

.8 2.0 2.2 2 .4 2.6 2.8 3.

NOZZLE PRESSURE RATIO , ptn /po

a) CIRCULAR NOZZLE NO. 1

Figure

10.

Jet wake dynamic pressure degradation for various nozzle pressure ratios,

31


34/81

0

5

0

I-

*

30

N O Z Z L E

0

0

35

6

6

p t /Po

n-

2.01

1.50

45

AX IAL DISTANCE FROM NO ZZ LE EXIT/EQUIVALENT CIRCULAR NO ZZ LE DIAMETER

, Z/D,

Q

e

W

i

I

I

I

I

i

I

I

2.2-

NOZZLE PRESSURE RATIO

p

2.4

/

Po

.~

UD.5

0

2

4

6

8

10

12.5

15

17.5

20

25

30

40

1

I

I

2.8

(b)

R EC TAN GU LAR N O L Z E

NO.

6

( A l =

6)

Figure 10. Continued.

32


35/81

NOZZLE

~

X

0

0

I

I

I

I

35

15

3

2

.--c

2.

45

50

AXIAL DISTANCE FROM NO ZZ LE EXIT/EQUIVALENT CIRCULAR NO ZZ LE DIAMETER

,

Z/D,

2 1.0-

1

2 1

* 8 1

I

I

I

2 1

0 -

.41

1 .o

~

1

2.2

2.4

2 . 6 2.8

NOZZLE PRESSURE RATIO

p t n

/

p

(c)

DELTA NOZZLE NO.

9

( A = 5,@= 30 )


33


36/81

NOZZLE

Ptn- /Po

2.36

0

0

12

12

12

I

I

I

i

I

2.01

1.50

5 10 1

AXIAL DISTANCE

FROM

N O ZZ LE EXIT/EQUIVALENT CIRCULAR NO ZZ LE DIAMETER

,

Z/D,

_ _

.

2

, .

t

.1

I

i

A:

1

I

2.2

El

a

P

cl

a

0

10

I

20

g

2.0

::t

.

2.6

-

2.

NOZZLE PRESSURE RATIO ,

tn

po

(d)

TWELVE SEGMENT NOZZLE

NO. 12

Figure

10.

Concluded.

34


37/81

(a)

CIRCULAR NOZZLE NO. 1

i

+

F=

I

I

0.6li

(b)

-ECTANGULAR NOZZLE

NO.

5

(A?

= 1 )

DISTANCE

FROM

NO ZZ LE EXIT/EQUIVALENT CIRCULAR N OZ ZL E DIAMETER

,

/De

Figure

11.-

Jet wake

dynamic pressure maps.

35


38/81

X AXIS

DISTANCE FROM NO ZZ L E EXIT/EQUIVALENT CIRCULAR NOZ ZL E DIAMETER

,

/De

(c) RECTANGUL AR NOZZL E

NO. 61_R =6)


36


39/81

X AXIS

+4

Y AXIS

i

DISTANCE

FROM

NO ZZ LE EXIT/EQUIVALENT CIRCULAR NO ZZL E DIAMETER

,

/De

(d) DELTA NOZZLE

NO. 8 R = 5,

B = 5 )


37


40/81

Y

AXIS

DISTANCE

FROM

NOZZL E EXIT /EQUIVAL ENT CIRCULAR NO ZZ L E DIAMETER

,

/De

(e)

D EL TA N O Z Z L E NO. 9

(

.4 = 5 , b= 30')

Figure

11. -

Continued.

38


41/81

X AXIS

i r r r r

+4

I 1

0

rrrrr

a

DISTANCE FROM NO ZZ L E EXIT /EQUIVAL ENT CIRCUL AR NOZ ZL E DIAMETER , /De

( f )

TWELVE

SEGMENT

N O Z Z L E NO. 12

Figure 11.- Concluded.

39


42/81

.1111

....

111111

I I1 11111111 I 1 II I I 1 1 1

I1

I I 1111 1 1 1 1 . 1 1 1 1 1 1 1 I I I I I

,111

I,

I

G EO ME TR Y O F M I X I N G ZONE

BOUNDARY OF

0.

25qz

"APPARENT CORE" \ mox

DISTANCE FRO M JET A XIS TO BOUNDARY OF "APPARENT CORE'. '

\

AXIAL DISTANCE FROM NO ZZ L E EXIT /

EQUIVALENT CIRCULAR NO ZZ L E DIAMETER, Z/D e

A

= 4

Figure 12. - Definition of mixing zone geometry

for

similarity analyses.

40


43/81

25%

REFERENCE CONTO URS

0

4

N O Z Z L E

0

1 SMO OTH CIRCULAR

-

2

SANDPAPER INSERT

i l

I I

I I

1 1

I I,

I I

1 1

fl

8 12

d

16 20

AXIAL DISTANCE FROM NO ZZ LE EXIT/EQUIVALENT CIRCULAR NO ZZ LE DIAMETER - Z/De

SIMILARITY PROFILES

NO. 2

IMILARITY PROFILES NO.

1

0

.4 .a 1.2

TRANSVERSE M IX IN G DISTANCE RATIO,

x/x.25qz

(a)

CIRCULAR NOZZLES NO.

1

B

2

mOX

Figure 13.- Jet wake 25%

reference

contours and similari ty profiles.

1.6 2.0

41


44/81

25% REFERENCE CONTOURS

B

E

\

P

4

E

Iz

Z

>-

n

0-

I

CFD Dynamic Pressure and Thrust Characteristics of Cold Jets Discharging From Several Exhaust...

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