In the fuel preburner of the Space Shuttle Main Engine, face plate, injector, and baffle erosion have been observed. The observed patterns of erosion suggest that flame attachment to the walls is a contributing factor. To better understand the physical phenomena involved, a portion of the preburner was modeled computationally. The simulated 'preburner' had three two-dimensional jets entering a cavity adjacent to a baffle. The computational model employed the Patankar Spalding algorithm with upwind differencing. The turbulence model was a standard k-epsilon model with wall functions. The effects of incoming boundary conditions on turbulent kinetic energy and dissipation, k and epsilon, was studied. The results indicate a very strong sensitivity to these boundary conditions over certain ranges of values

Campbell, W.

English

NASA Technical Reports Server

NASA 
Technical 
Memorandum 
NASA T M - 8 6 5 4 1  
A COMPUTATIONAL STUDY OF MULTIPLE JET 
AND WALL INTERACTION 
B y  Warren Campbell  
Systems Dynamics Labora to ry  
National Aeronautics and 
Space Admi ntstratton 
George C. Marshall Space Flight Center 
MSFC - Form 3190 (Rev. May 19831 
https://ntrs.nasa.gov/search.jsp?R=19860015466 2020-03-20T15:31:57+00:00Z

TABLE OF CONTENTS 
, 
Page 
INTRODUCTION ............................................................. 1 
PREBURNER MODEL .......................................................... 3 
EFFECT OF UPSTREAM BOUNDARY CONDITIONS ............................. 4 
MESH DEPENDENCY .......................................................... 7 
SUMMARY .................................................................... 7 
REFERENCES ................................................................. 8 
LIST OF ILLUSTRATIONS 
Figure Title Page 
1. Baffle and injector configuration for the fuel preburner ............. 1 
2. Erosion patterns in the fuel preburner suggestive of 
the Coanda effect ................................................... 2 
3. Model preburner showing boundary conditions and sample 
uniform recirculation zone calculation ............................... 3 
4 .  Preburner f low for turb = 0.01 ..................................... 5 
5. Preburner flow for turb = 0.001..  .................................. 6 
6.  Recirculation zone length as a function of the upstream 
boundary condition on turbulent kinetic energy ..................... 6 
iii 
TECHNICAL MEMORANDUM 
A COMPUTATIONAL STUDY OF MULTIPLE JET AND 
WALL INTERACTION 
INTRODUCTION 
Combustion of hydrogen and oxygen in the preburner of the High Pressure 
Fuel Turbopump of the Space Shuttle Main Engine drives the turbine and energizes 
the pump which circulates hydrogen fuel through the engine. 
has 264 coaxial injector elements and three baffles (Fig. 1). 
The fuel preburner 
Erosion patterns on the preburner faceplate and baffles suggest that the injec- 
The preburner operates in a very fuel rich condition and efforts are made 
tor jets have attached to the walls. 
Figure 2.  
to keep combustible oxygen away from walls by using sheets of hydrogen. 
Examples of this type of erosion are given in 
The fluid in the outer concentric jet of each injector element is hydrogen. 
most instances, baffle or wall discoloration or erosion have been attributed to this 
outer hydrogen sheet being disrupted by contamination lodged in the narrow clearance 
between the inner and outer annuli of the injector. In some cases, the obstructing 
contamination was located during visual inspection. In other instances, no contamina- 
tion was apparent. 
In 
FUEL INLET (REF) 
li 
FGld 
FUEL PREBURNER 
BAFFLES 
Q 
Q 
Figure 1. Baffle and injector configuration. 
for the fuel preburner . 
cd a 
a, 
5 
F1 
.rt 
[II 
2 
When significant erosion occurs, repairs are made on faceplate and baffles and 
the central, oxygen-injector region is plugged permanently. In the course of testing 
the development engines, a number of the injector elements may be pinned shut. At 
present, all six of the outer wall-baffle corner-injector elements ( H l ,  H 1 8 ,  H 1 9 ,  H 3 6 ,  
H 3 7 ,  and H 5 4 )  are pinned before testing. In the course of testing, wear and erosion 
make the pinning of additional injector elements encessary. 
pinned, erosion becomes more likely. Because each central injector element is fed upstream 
by a common oxygen supply manifold, the normal flow through pinned elements i s  
rerouted through the other unpinned elements. 
operate in a more oxygen rich mode making the remaining unplugged injectors burn 
hotter and erosion more likely. 
A s  more and more are 
This causes the injector elements to 
This study was initiated to investigate the possibility that contamination might 
Jet attachment to adjacent not always be required to cause wall and baffle erosion. 
walls, i-e. ,  the Coanda effect, is studied as an alternative mechanism. 
PREBURNER MODEL 
A two-dimensional "preburner" consisting of three jets, a baffle, and symmetry 
Figure 3 depicts the boundary conditions and a sample boundaries are investigated. 
calculation. 
Patankar Spalding algorithm [l] with upwind differencing. Reynolds number of the 
incoming jets, based on jet diameter, was 6,000,000.  Turbulent closure was accom- 
plished using the k - E  model with wall functions 121. 
Computational modeling was done with a version (PHOENICS) of the 
FRICTIONLESS BOUNDARY 
Figure 3 .  Model preburner showing boundary conditions and sample 
Z 
E 
R 
0 
P 
R 
E 
S 
S 
U 
R 
E 
uniform recirculation zone calculation. 
3 
Referring to Figure 3,  the dimensions of the flow 
The incoming jet dia 
s paper, the cross-st 
Downstream 
but for this st 
The computational grid was composed of 94 
and 51 in the longitudinal direction. This basic 
but was expanded to 94 by 100 for one run to t 
EFFECT OF UPSTREAM BOUNDARY CONDITIONS 
Initially, a nonunique solution of the steady equations was anticipated as a 
result of the Coanda effect. 
was given a positive y component of velocity and a converged solution wap obtained. 
Beginning again from the converged, perturbed solution but with an unperturbed bound- 
dary condition, a new solution was calculated. In early runs, a nonunique solution 
was obtained, but with an unrealistic downstream pressure bou ry condition. The 
length of the calculation domain was so short that a downstream zero pressure bound- 
ary condition was physically unrealistic. 
farther away from the inlet, the calculated flow appeared to be unique. 
To test for the suspected Coanda effect, the central jet 
When the boundary condition was moved 
Next, a parametric study of changes in upstream boundary conditions on k and 
E was done. Inlet values for k and E were input according to equations (1) and ( 2 ) .  
E. 111 = d k h  3 /2 /L  . 
In these equations, turb and d were constants, and L is a fixed turbulent length 
scale. For the k- E model, the effective viscosity is calculated from equation ( 3 ) .  
( 3) 2 = 0.09 p k / E  + u l  . 'e 
Here p is the fluid density, and p is the fluid laminar (molecular) viscosity. 
From the above three equations, if the incoming kinetic energy of turbulence is 
increased, the incoming viscosity increases as k1l2. The effective viscosity affects 
diffusion of mean energy of the flow. 
diffusion would increase. Increased diffusion means that recirculation zones should 
decrease. In spite of these expectations, the contrary result was obtained. A s  the 
If 1-1 e increases, one would expect that the 
4 
incoming kinetic energy was increased, the extents of the four recirculation zones 
increased, 
the size of the recirculation zones is expected. 
This  is obviously a computational effect because physically a reduction in 
The effect described above was elimjiiated by fixing the incoming value of E at 
a constant value as the incoming kinetic energy was varied. 
variation of recirculation length wi th  input kinetic energy was obtained over a fairly 
broad range of values. Even here some care was necessary. 
In this case the correct 
To illustrate, a class of problems were run in which turb was varied from 0.001 
2 3  to 0 .1 .  
values of incoming kinetic energy. 
recirculation zones increased in length as  expected. 
tu rb  in this range is shown in Figure 4 .  
tin was fixed at 191,000 m /sec . This value of E. is consistent with high ln 
A s  turb was decreased from 0 .1  to 0.01, all four 
A typical set of streamlines for 
1 
Figure 4. Preburner flow for turb = 0.01. 
A s  turb was made smaller than 0 .01 ,  an unusual effect was observed. Before, 
When turb was set below 0.01, 
all four recirculation zones (1 to 4 counting from the baffle) remained approximately 
the same length and increased with decreasing turb.  
shortened while 2 and 4 remained long. 
Figure 6 depicts the change in recirculation zone length wi th  turb.  All  four curves 
have similar variation for 0.01 5 turb 5 0.1.  For turb < 0.01, the curves for zones 
2 and 4 reached a maximum l i m i t  while the curves for zones 1 and 3 experienced a 
discontinuous decrease. 
P the result depicted in Figure 5 was obtained. Recirculation zones 1 and 3 were 
The result was both dramatic and abrupt. 
This effect was quite stable. An iteration begun with a converged solution for 
turb = 0.009, but with turb = 0 .01  for the new run, ends up with a solution con- 
sistent with turb = 0.01. The reverse was also true. A s  desired, the final solution 
is sensitive to the boundary conditions but not to the initial guess. 
5 
Figure 5. Preburner flow for turb = 0.001. 
- RECIRCULATION ZONE 1 
---RECIRCULATION ZONE 2 
RECIRCULATION ZONE 3 
-*-RECIRCULATION ZONE 4 
RECIRCULATION 
L LENGTH 
0 INLET JET 
DIAMETER 
- =  
10 
8 
6 
4 
2 
0 
t 
I 
10 1 0.01 
TURB 
(kin = TURB * Uin*) 
P 
a 
1 
Figure 6 .  Recirculation zone length as a function of the upstream boundary 
condition on turbulent kinetic energy. 
6 
If the value of E. was decreased to a value consistent with turb = 0.01, the 
The next step in this study is to 
in 
discontinuous behavior was no longer observed. 
vary this value of over a range and see where the discontinuity begins. 
MESH DEPENDENCY 
The flow calculations presented above were done with a 94 by 51 mesh. To 
determine the amount of grid dependency, a mesh 94 by 100 was used. Turb was set 
at 0.009, and a nonuniform pattern of recirculation zones was observed as before but 
with one difference. Whereas before the recirculation zones were in the pattern of 
long-short-long- short, for the refined mesh the pattern was short-long-short-long! 
Obviously, no claim for grid independence can be made at the present time. 
plans call for finer mesh solutions. 
Future 
SUMMARY 
A two-dimensional model rTpreburner7r was investigated in an attempt to simulate 
conditions which result in preburner wear in the Space Shuttle Main Engine. 
physically realistic conditions, no multiple steady-flow solutions were observed. Wall 
attachment was observed in every instance. While significant, drawing conclusions 
about the real preburner based on these results should be done carefully since not 
all aspects of the f low were included in the simulation, e .g . ,  the coaxial nature of 
the jets. 
For 
A range of phenomena were observed which as yet are poorly understood. The 
discontinuity and nonuniformity of the recirculation zone lengths is the prime example. 
If the effect is a physical rather than a numerical phenomenon, then it would have 
a significant effect on the performance of the preburner. 
can be drawn as to whether or  not it is a real physical effect. 
At present no conclusion 
7 
REFERENCES 
1. Patankar, S. V .  and Spalding, D .  B . :  A Calc 
and Momentum Transfer in Three-Dimensional P 
Mass Transfer, Vol. 15, p .  1787. 
2.  Launder, B .  E .  and Spalding, D .  B . :  The Nu ion of Turbulent 
Flows. Comp. Meth. in Appl. Mech. Eng., Vol. 3,  19 
8 
APPROVAL 
A COMPUTATIONAL STUDY OF MULTIPLE JET AND 
WALL INTERACTION 
By Warren Campbell 
The information in this report has been reviewed for technical content. 
of any information concerning Department of Defense or nuclear energy activities or 
programs has been made by the MSFC Security Classification Officer. This report, 
in its entirety, has been determined to be unclassified. 
Review 
G .  F. McDONOUGH . 
Director, Systems Dynamics Laboratory 
r 
*U. S. GOVERNMENT PRINTING OFFICE 1986-631Q58/20103 
9 
TECHNICAL REPORT STANDARD T I T L E  PAGf 
1.  REPORT NO. 2. GOVERNMNT ACCESSION NO. 3. RECIPIENT’S CATALOG NO. 
NASA TM -86541 
a TITLE AND SUBTITLE 5. REPORT DATE 
A Computational Study of Multiple Jet and 
Wall Interaction 
7. AUTHOR(S) I 8. PERFORMING ORGANI Z A T ~ O N  REPOR r J 
I 
February 1986 
6. PERFORMING ORGANIZATION CODE 
Warren Campbell 
3. PERFORMING ORGANIZATION NAME AND ADDRESS - t  10. WORK UNIT, NO. 
1 A-1 rl I ’  \ 
George C .  Marshall Space Flight Center t 1. CONTRACT OR GRANT NO. 
Marshall Space Flight Center, Alabama 35812 ’ 
13. TYPE OF REPOR; & PERIOD COVERE1 
2. SPONSORING AGENCY NAME AND ADDRESS 
National Aeronautics and Space Administration 
Washington, D .C . 20546 
Technical Memorandum 
1.1. SPONSORING AGENCY CODE 
I 
5. SUPPLEMENTARY NOTES 
Prepared by Atmospheric Sciences Division, Systems Dynamics Laboratory, 
Science and Engineering Directorate. 
6. ABSTRACT 
In the fuel preburner of the Space Shuttle Main Engine, face plate, injector, 
The observed patterns of erosion suggest and baffle erosion have been observed. 
that flame attachment to the walls is a contributing factor. To better understand the 
physical phenomena involved, a portion of the preburner was modeled computationally. 
The simulated qlpreburnerlf had three two-dimensional jets entering a cavity adjacent 
to a baffle. The computational model employed the Patankar Spalding algorithm with 
functions. 
to these boundary cond’tions over certain ranges of values. 
upwind differencing. 
and dissipation, k a n d a  was studied. The results 
The turbulence model was a standard 
The effect of incoming bouqdary conditions on 
7. KEV WORDS 
Turbulence 
Fluid Dynamics 
Computational Fluid Dynamics 
Separated flow 
Jets 
Turbulent mixing 
9. SECURlTY CLASSIF. (ol thh report) 120. SECURITY CLA! 
18. DISTRIBUTION STATEMENT 
Unclassified - Unlimited 
1 F. (02 this pas.) 121. NO. OF PAGES 122. PRICE 


A computational study of multiple jet and wall interaction

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