Analysis of turbulent combustion and stability characteristics in liquid propellant rocket engines

Date

2023-12

Author

Öztürkmen, Musa Onur

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Combustion instability is a critical phenomenon in the field of combustion dynamics. It occurs as a result of the complex interplay of fluid dynamics, heat transfer, and chemical kinetics within combustors, resulting in undesirable, self-sustaining pressure oscillations and hence posing considerable difficulty in the design and operation of various combustion systems. Therefore, predicting combustion instability and mitigating it during the design of a combustion chamber is critical. The main objective is to develop a computational framework for characterizing the chamber dynamics of liquid propellant rocket engines under linear thermoacoustic effects, which can be used to assess stability characteristics for safe operation. The linear thermoacoustic stability of a combustion chamber may be determined by solving the nonhomogeneous wave equation with the interactions between the acoustic and heat release fluctuations, which are usually encoded in a flame transfer function. Due to the frequency dependent nature of it and the chamber boundary conditions, the problem becomes a nonlinear eigenvalue problem with frequency dependent coefficient matrices. This nonlinear problem requires linearization to reduce it to a solvable form. Three different linearization approaches are investigated in this study, one of which is proposed within the scope of the thesis, and all of them result in an iterative algorithm. The proposed solution methodology is implemented and validated against a canonical problem. An experimental combustor, also known as a Continuously Variable Resonance Combustor (CVRC) in the literature, is also studied to acquire the frequency dependent flame transfer functions required in thermoacoustic calculations by utilizing large eddy simulation (LES) for verification purposes. The acquired results of the study show that the proposed solution methodology and linearization approach perform well, especially with frequency dependent source terms.

Subject Keywords

Helmholtz equation, Thermoacoustic instability, Frequency dependent flame transfer function, Nonlinear quadratic eigenvalue problem, Impedance boundary condition

URI

https://hdl.handle.net/11511/107675

Collections

Graduate School of Natural and Applied Sciences, Thesis