No abstract

Concurrent experiments and computations are used to analyze combustion instabilities in a transverse mode combustion chamber. The experiments employ a shear-coaxial injector element, positioned within a rectangular chamber and driven by high amplitude transverse acoustics modes by unstable injector elements located near the chamber end-walls. The reacting flow portion of the study element is optically accessible and the chamber is extensively instrumented with high-frequency pressure transducers. Different levels of instability are obtained by varying the operation of the driving elements. High-fidelity computational fluid dynamics simulations are used to model this set-up, although only the study element is fully represented and the transverse acoustics modes are generated by vibrating the side walls at the appropriate frequencies. The computational results are compared quantitatively with the high frequency pressure measurements, and qualitatively by using the CH* chemiluminescence signal from the experiment. The combustion response of the first, second and third transverse modes obtained using a dynamic modal decomposition procedure show excellent agreement between the experiments and simulations. The overall approach shows significant promise for screening the combustion response of candidate injector configurations for rocket applications.

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Computational fluid dynamics simulations are used to study spontaneous combustion instabilities in a rectangular chamber that contains seven coaxial injector elements. The simulation predicts self-excited transverse oscillations that have variable amplitudes, similar to what is seen in a companion experiment. Several processes are identified in the simulation that may promote the rise of instability by increased heat release during a local compression, including the interaction between vortices shed from adjacent injectors and interactions between flames and the combustor walls.