An experiment to study the physical agents that are responsible for the jet turning into the streamwise direction, and the mixing of the jet and the cross stream fluid in the case of a jet in a cross flow is discussed

Foss, J. J.

Wark, C. E.

English

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INFLUENCE OF A  LARGE FREE STREAM DISTURBANCE LEVEL ON 
DYNAMICS OF A JET I N  A CROSS FLOW 
John J. Foss and Candace E. Wark 
Department o f  Mechanical Engi n e e r i  ng 
M i  c h i  gan S t a t e  U n i v e r s i t y  
Eas t  Lans i  ng, Mi c h i  gan 48824 
INTRODUCTION 
J e t s  o f  r e l a t i v e l y  h i g h  speed (V .) and low temperature ( T . )  a r e  
J J 
o f t e n  used, i n  a  gas t u r b i n e  combustor, t o  coo l  t h e  gases and t o  quench 
t h e  chemical r e a c t i o n s .  The p r i o r  s t u d i e s ,  of t h i s  p a r t i c u l a r  c l a s s  
o f  t h e  " j e t  ' i n  a  c ross  f low"  problem have commonly been executed 
2 2 w i t h  t h e  s p e c i f i c  momentum f l u x  r a t i o  [p.V.  /pOUO 1 as t h e  p r imary  
J J  
v a r i a b l e ,  va lues o f  10-100 c h a r a c t e r i z e  t h e  range o f  t e c h n o l o g i c a l  
i n t e r e s t  f o r  t h e  combustor c o o l i n g  problem. 
The j e t  i n  a  c ross  f l o w  may be subd iv ided  i n t o  two general  
r e g i o n s :  " i n t e r a c t i n g "  and "downstream". Our i n t e r e s t  i s  i n  t h e  
former  and i n  t h e  p h y s i c a l  agents t h a t  a r e  r e s p o n s i b l e  f o r  the :  " j e t  
t u r n i n g  i n t o  t h e  streamwise d i r e c t i o n "  and t h e  m i x i n g  o f  t h e  j e t  and 
t h e  c r o s s  stream f l u i d .  A r e p r e s e n t a t i o n  o f  t h e  i n t e r a c t i o n  r e g i o n  
f o r  i so the rma l  m i x i n g  a t  (V . /U ) - 3.0 i s  shown i n  F i g u r e  1  ; t h i s  
J 0 
f i g u r e ,  f rom Foss [1980], serves t o  c h a r a c t e r i z e  t h e  i n t e r a c t i o n  
r e g i o n .  
The p r i o r  research  s t u d i e s  o f  t h i s  problem have used wind t u n n e l s  
f o r  t h e  c ross  strear!i; a  concomi tant  a t t r i b u t e  o f  these s t u d i e s  has been 
t h e  presence o f  a  low f r e e  stream d i s t u r b a n c e  l e v e l .  The purpose o f  o u r  
https://ntrs.nasa.gov/search.jsp?R=19830020946 2020-03-22T00:51:06+00:00Z
investigation i s  to  provide direct observations of the j e t  trajectory 
and mixing in the presence of a  large disturbance condition. There 
are two dis t inct ive features of our investigation. These are described 
below. 
The flow fac i l i t y ,  of the MSU Free Shear Flows Laboratory 
(Figure Z ) ,  provides a  large, planar, shear layer for use in the present 
study. Specifically, we have placed the j e t  (d  = 10mm) such that  i t  j 
exhausts into the middle region (7/uo = 0.5) of the shear layer a t  the 
end of the 3 meter t e s t  section. The local vort ic i ty  thickness (6w) i s  
large with respect to the j e t  diameter 6 /d - 58. Based on t h i s  j e t  
w j 
diameter, the turbulence f  i  1 ed i s  essential ly homogeneous. (The 
gradients of the mean velocity and the turbulence intensity are con- 
sidered to cause second order effects ;  the influence of these dis- 
tributions could be examined with appropriate numerical models of the 
flow.) The detai ls  of the experimental f ac i l i t y  are shown in Figures 
3 to 4 .  
The second distinctive feature of our study i s  the use o f  an 
array of 76,  f a s t  response ( T Z  0.1 msec) thermocouples to document 
the instantaneous temperature f ie ld  a t  the "end" of the interaction 
region. Specifically, the array will be placed in the flow, as shown 
in Figure 3 and the complete se t  of simultaneously sampled thermo- 
couple voltages will provide discrete values t o  characterize the 
temperature f ie ld :  T(yy z ,  t . ) .  . The temperature f ie ld  measurements 3 
will be repeated such 2.5 msec; hence, both the instantaneous f ie ld  
and i t s  temporal evolution will be evaluated. For comparison, the 
experiments will be repeated in the undisturbed, high speed, region of 
the flow f ie ld .  
The "planes" of t he  ins tantaneous temperature f i e l d  p rov ide  a 
unique da ta  base f o r  t he  e v a l u a t i o n  of t h e  t r a j e c t o r y  and t h e  m i x i n g  
o f  a  " j e t  i n  a  c ross  f l ow . "  The temperature data, i n  t h e  und is tu rbed  
cross stream, w i l l  be used t o  extend our  unders tanding o f  t h i s  bas i c  
f l o w  f i e l d .  The comparat ive measures: w i t h  and w i t h o u t  a  d i s t u r b e d  
c ross  stream, w i l l  be used t o  i d e n t i f y  t h e  i n f l u e n c e  o f  t h i s  d i s -  
turbance parameter on t h i s  f l o w  f i e l d .  
Figure 1. Schematic r e p r e s e n t a t i o n  of a " l a rge  R" j e t  i n  a c r o s s  
flow from Foss 119791. 
Notes : - . . . . . schematic  r e p r e s e n t a t i o n  of t h e  observed shea r  l a y e r  
i n s t a b i l i t y  
- 
..... schematic  r e p r e s e n t a t i o n  of t h e  v o r t i c i t y  vec to r .  
Sur face  s t r e s s  and A , B  , ~ , d  f l u i d  t r a j e c t o r y  l i n e s  have been t r aced  
from t h e  a p p r o p r i a t e  photographs ... t h e i r  p o s i t i o n s  a r e  shown t o  
proper  s c a l e  w i t h  r e s p e c t  t o  t h e  j e t  h o l e  diameter .  
The "shroud" of f l u i d ,  which covers  t h e  f l a n k s  of t h e  wake r eg ion  
and which is  marked t o  t h e  sheared fluid f r o m  t h e  A and B i n p u t s ,  
is no t  shown. 
The forward s t a g n a t i o n  nodes (N1,N2), a s  shown i n  F igure  33, e x i s t  
f o r  t he  l a r g e  R cond i t i on ,  they  a r e  only shown e x p l i c i t l y  i n  t h a t  
f i g u r e  . 
The "1, 61, a 2 ,  s t r e a m l i n e s  and t h e  c r o s s  hatched s e c t i o n  of t h e  
j e t  r ep re sen t  c o n j e c t u r a l  e s t ima te s  of t h e  flow behavior .  The forme 
a r e  t o  show t h e  presence  of a s h a r p ' d i v i s i o n  between jet  and c r o s s  
s t ream f l u i d  and t h e  formation of t h e  bound vo r t ex  from t h e  i n t e r -  
a c t i o n  of t hese  two streams.  
FREE SHEAR FLONS LAKFUCRY 
ALL M M l O N S  ARE N M T E R S  
DO m w  
Figure  2. Flow f a c i l i t y ;  MSU f r e e  Shear Flows Laboratory 
Figure 3. Schematic representation of the flow field, the 
Thermocouple Sampler, and Instrumentation 
82 
Placement fork 
Individual thermocouple el  ements of the modular element 
Figure 4 The thermocouple array support member. 
Notes: All elements shown to correct physical s i ze ,  


Influence of a Large Free Stream Disturbance Level on Dynamics of a Jet in a Cross Flow

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