NASA 

Technical 

Memorandum 

NASA TM-86541 

A COMPUTATIONAL STUDY OF MULTIPLE JET 

AND WALL INTERACTION 

By Warren Campbell 

Systems Dynamics Laboratory 

National Aeronautics and 

Space Admi ntstratton 

George C. Marshall Space Flight Center 

MSFC - Form 3190 (Rev. May 19831 

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 flow 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 injecThe 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 contamination 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 (Hl, H18, H19, H36, 

H37, and H54) 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 is 

rerouted through the other unpinned elements. 

operate in a more oxygen rich mode making the remaining unplugged injectors burn 

hotter and erosion more likely. 

As more and more are 

This causes the injector elements to 

This study was initiated to investigate the possibility that contamination might 

not always be required to cause wall and baffle erosion. Jet attachment to adjacent 

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 

boundaries are investigated. Figure 3 depicts the boundary conditions and a sample 

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 accomplished 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 bounddary 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 boundary 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 =dkh 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 + ul . '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. As 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 with 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 

23 to 0.1. 

values of incoming kinetic energy. 

recirculation zones increased in length as expected. 

turb 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 

As 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. 

As 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 with 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 limit 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 consistent with turb = 0.01. The reverse was also true. As 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 flow 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 TITLE 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 ZAT~ON 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, 

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 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 anda 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 

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