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For given acoustic frequencies of premixed gas-turbine combustors, a classical method not currently in use is explored for assessing whether acoustically driven oscillatory combustion will occur. The method involves cataloging linear amplification and attenuation mechanisms and estimating magnitudes of their rates. Linear approximations to nonlinear mechanisms are included in an effort to obtain a reasonably complete description. A stability index is defined such that oscillation is predicted to occur when the value of the index exceeds unity. The method is tested on the basis of new experiments and experimental data available in the literature. Moderate success is achieved in rationalizing these experimental results. The objective of the method is to enable quick and inexpensive decisions to be made for a wide variety of potential design configurations and operating conditions, without the complexity of computational fluid dynamics. The approach therefore may complement other approaches already in use.Copyright © 2007 by ASME

A new approach for modeling combustion instabilities using acoustic energy conservation is proposed. This approach allows the flexibility to calculate contributions from amplification and/or attenuation across all frequencies, rather than predicting eigenmodes. It is likely that such a direct acoustic energy approach could be of benefit in determining the susceptibility of all frequencies to growth or decay as operating conditions in a gas turbine change. This approach may also give designers a method for improving passive damping in the initial design phase, with the ability to scan various frequencies and investigate the susceptibility to oscillatory instability at different operating conditions. A linear model, including linear approximations to nonlinear processes, is introduced whereby the mechanisms contributing to amplification and damping of acoustic energy are assessed independently to find a net amplification coefficient, a reciprocal time (or a rate). Stability for each frequency is assessed by examining a ratio between amplification and damping. It is anticipated that this effort may provide a useful new perspective on and enhanced prediction capability for combustion oscillatory instabilities.Copyright © 2006 by ASME