CAREER: Control of Acoustic Instabilities in Large Combustors

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Abstract: For reasons not entirely understood, combustion chambers that favor high efficiencies and low emissions often exhibit combustion instabilities. These instabilities arise due to a regenerative coupling between chamber acoustics and thermal fluctuations. Some instabilities appear as limit cycle oscillations in the flow variables of basic propulsion and power generation systems. Examples include rocket motors, ramjet engines, gas turbines, afterburners, and large industrial combustors. The research phase of this project aims at developing a comprehensive stability algorithm that can be used as a diagnostic tool in the developmental stages of large combustors. The newly developed algorithm will be based on the latest technological advances that suggest incorporating the effects of acoustical, thermal and vortical waves from the ground up. The new representation of chamber acoustics will permit estimating the growth or decay of the system energy with most rotational flow effects accounted for. In the process, a generalized mean-flow description that mimics realistic chamber conditions will be employed. This representation is expected to enhance the accuracy of both linear and nonlinear stability equations used in the literature. The anticipated improvements in acoustic energy gains are also hoped to explain experimental findings that elude the present stability assessment methodology. As a windfall, it is projected that the origins of several injection-driven instabilities observed in solid, liquid and hybrid rocket motors will be illuminated. The educational phase of this career development plan describes a sequence of activities to be undertaken during the funding period. These include incentives for undergraduate curriculum development, initiatives for promoting research opportunities for both graduates and undergraduates, initiatives for encouraging interdisciplinary interactions, course enhancement methodologies, and recruitment of underrepresented groups.