Control and Prediction of Acoustic Instabilities in Large Combustors

It is well known that 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 devices. Examples include rocket motors, ramjet engines, gas turbines, preburners, afterburners (or augmentors), and large industrial combustors. Our recent work has focused on developing a comprehensive stability algorithm that can be used as a diagnostic tool in the developmental stages of large combustors. The newly developed algorithm is based on the latest technological advances that suggest incorporating the effects of acoustical, thermal and vortical waves into the energy equation. 

The new representation of chamber acoustics permits 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 is obtained. This representation enhances the accuracy of both linear and nonlinear stability equations used in industry. The improvements in acoustic energy gains also help to explain experimental findings that elude the present stability assessment methodology. The work helps to explain the origins of several injection-driven instabilities observed in solid, liquid and hybrid rocket testing. Our team is currently engaged in evaluating the hydrodynamic energy contributions that must be appended to the most recently developed combustion instability framework.  Our research results are implemented by Software and Engineering Associates and Gloyer-Taylor Laboratories.