Ph.D. Thesis Proposal

Christopher Lioi

Thursday, November 30rd, 10:00 A.M.

Montgomery Knight 317

Theoretical Acoustic Stability Analysis of Oxidizer-Rich Staged Combustion Engine Thrust Chambers

Dr. Vigor Yang (AE)

Dr. Lakshmi Sankar (AE)

Dr. Krish Ahuja (AE)

Dr. Timothy Lieuwen (AE)

Dr. Kenneth Cunefare (ME)

SUMMARY

The development and operation of liquid propellant rocket engines (LREs) remains hampered by the occurrence of combustion instabilities.  These large amplitude, coherent pressure disturbances result from complex feedback between unsteady combustion and the acoustic and hydrodynamic oscillations within the chamber.  Only a small portion of the energy liberated from chemical reactions must be transferred to the oscillatory motions for the resulting pressure amplitudes to become large enough to damage or destroy engine hardware.  For very energy dense systems such as LREs, the concern is especially high as the risk of catastrophic failure is increased.  Combustion instabilities have historically been addressed during the design stage of an engine in a rather ad-hoc manner.  Famously, the F-1 engine developed as part of the Apollo program underwent over 2000 full-scale tests before an acceptable configuration was achieved.  Such an empirical approach is expensive and time consuming, and better methods are required for accurately and consistently determining a priori the stability of a candidate engine.  Many theoretical investigations have materialized over the intervening decades but additional work is still needed, especially for systems with complex geometry and flowfields.

This thesis aims to broaden the existing capacity for combustion stability assessment by exploring the acoustics of a configuration representative of an oxidizer-rich staged combustion (ORSC) engine, and particularly one employing a gas-centered swirled coaxial (GCSC) injector design.  Whereas other configurations may be idealized acoustically as consisting only of the main thrust chamber terminated upstream by some impedance condition, this is insufficient for the engine described here.  A continuous gas phase region may be identified as connecting the main chamber to an oxidizer dome via the GCSC manifold, such that acoustic coupling with these components must be accounted for in a more comprehensive manner.  To this end, an eigenmode matching technique is employed to connect the three distinct subdomains and derive wave characteristics for the composite system.  Numerical results for the complex eigenfrequencies are compared with finite element solutions, and eigenvalue asymptotics will be employed to study the parametric dependence of the system stability on model inputs, particularly combustion response parameters.  As part of the investigation, a simplified combustion response model appropriate to the geometry and turbulent flow conditions will be developed.