Jets of low temperature air are introduced into the aft sections of gas turbine combustors for the purpose of cooling the high temperature gases and quenching the combustion reactions. Research studies, motivated by this complex flow field, have been executed by introducing a heated jet into the cross stream of a wind tunnel. The investigation by Kamotani and Greber stands as a prime example of such investigations and it serves as the principal reference for the present study. The low disturbance level of the cross stream, in their study and in similar research investigations, is compatible with an interest in identifying the basic features of this flow field. The influence of the prototypes' strongly disturbed cross flow is not, however, made apparent in these prior investigations

Foss, J. F.

Wark, C. E.

English

NASA Technical Reports Server

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• OF t_OC'_(_U/,,LII1
FREE STREAM TURBULENCE AND DENSITY RATIO EFFECTS ON THE
INTERACTION REGION OF A JET IN A CROSS FLOW1
9
C.E. Wark" and J.F. Foss
Dep.._z'tm_nt of Mechanical Engineering
Michigan State University
Jets of low temperatare air are introduced into the aft sections of gas
turbine combustors lot the purpose of eooiing the high temperature gases and
quenching the combustion reactions. Research studies, motivated by this
co_plex fl_,w field, havo been executed by introducing a heated jet into th T
cross stream of a wind tunnel. The investigation by Kamotani and Greb,_r
stands as a prime ,xample of such investigations and it serves as the prin.-
cipal reference for the present study.
The Low _isturbance level ot th- cross stream, in their study and i;, similar
research investigations, is compatible with :,n in, crest in identifying the
basic features, of this flow tield. The influ._n,:e ot the prototypes' stronglyt
; disturbed cross !low is not, however, made apparent in these prior
"" investigations. The present study provides a dire,:t com_arzson of the thermal
". field properties for a low {5/I; m = 0.67_,) and a high (O/V = 34_) r
disturbance level condition.
;
A novel technique, was used for th_ data acquisition (Figure 1). Sixty-four
tast response {_ : _m.qev) thermocouples wer,, simultaneously sampled {and
corrected for the tlm_ constant _,t'tect) at a downstream plane close to the jet
exit (x/d-3-4). Various measures were used to _haractorize Lhe thermal fields
for the disturbed ,rod undisturbed conditions, for two different momentum flux
,) ,)
ratios (J-ojV /p V -16,64), ,and for throe ove.'hear conditions
¢T.-22.2, a7.1 and 61.1).
3
Two forms of data acquisition w_,re used fez this study. Stochastic values i
were obtained |zorn triplet values: TK(t-_t _ , Tk(t) and Tk(t+6t) , where I
K=I 64 is l. he th_rmocouple designation and the tgt (_t=O 64_sec) values
, were used t- form the central dif/erence time d,,rivative from which the i
Tk( was determined Tilese values were,:orzer't,,d t,'mperatu['_ value: { t)}c,
retain,,d to_ t, t+ht, (+'.',t .... t+Nht where N=5,000 fo= the undisturbed and
lO,OOO fur tile di:;turbed ,'on,tit ion a_:d At=lOOms _;hich ensured the statSsttcal
independence fzom its neighhort,g value. Instantaneous samples: At • 0.64mi
and N-I _ ") _ ; ',,. wer- stored for J,,16, 64 and T. - 61.1 c. ,
1
2 Supported by NASA Grant NAG 3-245
M.S. 1084, presently at lllinole Institute of Technology
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....
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ORIGINALPAGE II
• OF POOR QUALlrY _'
RESULTS
- HistJgrams, formed from the independent samples, were sufficiently smooth to
approximate a probability density function; examples are shown in Figure 2 for
. a thermocouple from the central region of the jet. A striking result, from
all such histograms, is that the peak (non-dimensional) temperature did not
exceed 0.25. Hence, even at the relatively close x/d locations of the present
study, molecular diffusivity has played a dramatic role in the reduction of
the temperature for the fluid elements of the jet.
The individual histograms and the isothermal patterns that are fit to the
mean values of the corrected temperatures, both reveal that the magnitude of
the overheat exerts a significant dynamic effect on the !et in a cross flow
problem; see Figures 3 and 4. It is pertinent to note that the increasing
distance of the thermal center of gravity, from the source plate with in-
creasing jet temperature, is opposite to that which would be expected from
buoyancy and enhanced entrainment effects. The former agrees with the
Kamotani and Greber results, the latter is in disagreement. The physical
; reasons for this unexpected behavior are not apparent; the consistency of the i
_ trend: an increased penetration of the thermal field with an increased jet
temperature, _c conslstently observed and serves as a primary focus for
further study. A further comparison with the results from Kamotani and Greber
(see Figure 5) reveal_ a substantial difference between the jet penetration
• for the two studies. This difference is (at least in part) attributed to the
presert use of a sharp-edge nozzle and to the large (6/d = 1.3) boundary layer
for the present study.
One clearly apparent effect el the large disturbance condition is the mi-
gration of the centroid of the thermal f_eld; see figure 6. Similar data for
q_
all of the instantaneous scans (6 disturbed, 3 undisturbed) are summarized in
Table I; note: K is the normalized correlation coefficient between the
st
> vertical (s) and transverse (t) displacements of the thermal center of i
gravity.
TABLE 1. Cross strea-a disturbance effect
on centroid of temperature field
J o _ F
s t st
c.g. c.g.
undisturbed t'.f. 16 ,_41 .253 .067
undisturbed c.f. 64 .233 .233 -0.13
i
di sturbed c.f. 16 1.84 1.45 -0.33
di,Iturbed c.f. 64 1.16 1.12 -0.45
The lower mean values, of the disturbed cross stream mean isotherms, are '
apparently caused by these large centerline migrations; figure 7 shows an i-.
Instanta,.eous isotherm pattern that reveals maximum temperature values of the
same order as those for the undisturbed case.
- "'_ "164
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1984012457-160
:" .... -,",-_'- PAGE ISI f- (
: Oj: POOR QUALITY (
....." 1I'_ _-- $NSULAT iON .......
, ,T..O/ _ I ' /• ao_l[liSUiqE-- "* SOI • t, TAP I , :
i r , --
_ -_ _ SPI[NCER
,i BLOWEIq
_' TESt" BIEC110N _ / _ _o) 3.tnm
Ex.Ns,oN , .t \:) _ ,• L ..........
.... fl I/ /1_ -_
II|I|RINCI
"//Ir,'l/./'/l "/ If/IH|IM_O PAl _ I
Figure la. Schematic of Jet Supply and Exlt Conditions
Note: Lateral (I.e.,z) position of tllejet corresponds to the
.. undisturbed position. The jet exit was moved into the
, low speed portion of the shear layer: U/Uo=0.25, for the
disturbed flow condition.
ul
= X ;
!
i
o
i
i
L
"_ ( o :
-Z
h
L
C
l_,@urelb. Sc:..'_maticRepresentatlon ol Jet Trajectory, Showing Lab
coordinates (x, y, z) and Jet Coordinates ((, n, K)
Note: Themocouples were located in the y-z plane at x=3.5(for J-64)
and 3.85 (J'16).
165
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1984012457-161
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ORIGINALPAGE ig
• OF POOR QUALITY
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r. _ I Of 4 _0 CHANNIL
_HIBMOCOUPLIE BIEilINC| /•_i JUNCTION AND SIGNAL
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F;gureIc. SchematicRepresentationof the Temperature
measuren;ent system
m
166
1984012457-162
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: ROW M • t T++ |C_N_L
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+ " _ "I,.,, i t i __ • ,o
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Figure Id. Detail of a Sample and Hold Circuit• Ii
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1984012457-163
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ORIGINALPAGE i9
" OF POOR QUALITY
'_, 168
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1984012457-164
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ORIGL_ALP#,t3_ _':':'3
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, Figure2a. TemperatureHistogramforu.c.f.:J : 16,
'_ Thermocoupleat s/d • 4.79, t/d • 4.73
1984012457-165
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ORIGINALPAGE IS '_
OF POOR QUALITY'
t,
•. o . _ ,;,. e ,I _,
: .
: ll + + + + + ++ ++ + ll
+
+ i
+ +
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I
FJ Ure 31 undisturbed Cross Flow (u c f ) Nlln Tem_erstu I
9 " isotherms: J • 16. ? _ '. '1" • 22.2"C
" T je_ " *• 1
NOTE: Co,tours ShOWn.re _ I( I000 s/d. 14 I (  .7)- z,'d, il
t/d • 4.3(* .5) - yld
- 4 • 1E
1'I + 1" !
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• + +
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0 + + 0 I
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figure 3b. u.c,t, Mien Til_qperiture Isotherms: J • 15. Tie t - T , 61.1°C
NOTE: s/d • 14.1(+ ,7) - z/d, rid : 4,3(_ 5) - y/d
170
i 'i
1984012457-166
1984012457-167
.' ORIGINAL PAGE Ig
OF POOR QUALITY
I ISO;N.RM VA|U|I f
• I 2S-
0 1 J6 JO MAX
6 t WC ( 64 70 MAI C_D 64 i0 _ MAN
:*_ 1' '0 MAX
d ¢ f 64 40 _AX
• J 64 JD MAX
10'
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6
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d 50"_
l
25
(To- T.)"C !
Figure 4., Overheat Influence on s ComponentCentrotd
(L.aJcu|ited u_lnJ |_otherm cont(-urJ)
• Ra 4, _ " _a" )20 e]p (K and G)
• an 4l _ " _o ° 7_ oy (K and G)
10
•------.- Jet VolooLty OeutorlXne (l and C)
. • location of preleflt I component
/*/ I centroid (.l'16) T -T.1 41.7 C
//_ ° ap.,,.m., lo rio° of h ill
/7 _. 1 " temperature (3-16) T T • 41.7"C
:_' I -'-,-, ocat|on o| p:esent thermocoupSe array J "
,_
0 , _L _ I • , a t , . , i • I l *
o 5 x/_ 1o 1_ L
Fl_ur'e _4 Lo_aLton of Teiperature Centerllne (R-4)
from ka_t*_./ a.d Grehur (1971)
£
172
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1984012457-168
15 °/
•" /o °-_
_ --_ l_caton of In'eJent rh(.rmocouple array
/ • S,,8, T_- To- 320 oF (Kand_)
5 " R- 8, t_- T,- 75 "P _Kand(;) !
Je_ Velooi_ Cen_erllne (K anJ =_ ,+
aoprox_,_+lte I, _ _t.on _t the, "_.-,x_-ur _ r.eP_eraturo
0 .... t. TI.-_'" ", • * _ . _ .... _ L_
o 5 zo 1._
' lio
,_ from Kametan_ ._l,d ,.rcheT (}_'?}}
"_ . -- l_llillwk _I
i t • i i
t_5_----(,. /V /_ ._,, t _,_I..,'_ ; I_ R I
• l i t# t
_.°.++ ++:i +,,,_ i
¢ .,,= flee '
-P-,_¢_ i }
- I
I -a_+ - +,,, , "I ' r, ,'i " " +'' I" " ' '"I15.¢¢1 m.215 11.4_ e._! _.B_ ' ;
c lilNl tml
i '
- Figure6, Varlatlonof s Componentof CentroldwlthTime
! J • l_, Tiet + T - 61.I°C
i Note: (tc,g ,. tc.g.).dtstrlbutton drlwsI similarfluctultton level.
', 173
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1984012457-169
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• OF POOR QUALITY
0 4 t It
I
r|
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o I
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174
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1984012457-170


Free stream turbulence and density ratio effects on the interaction region of a jet in a cross flow

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