Simplified Description of Heat Release Oscillations for Assessing Combustor Stability

Abstract

A simplified description of heat release oscillations associated with vortex-driven combustion instabilities is developed that can greatly reduce the amount of data required for determining the linear stability of combustor eigenmodes. The simplification is achieved by first representing heat release fluctuations as sinusoidal oscillations and then modeling the amplitude of the oscillations using a heuristic assumption of proportionality between the mean and the fluctuating components of local heat release. It is shown that by simply knowing 1) the average heat release, and 2) the heat release at any particular phase of the oscillations, complete spatiotemporal description of heat release oscillations can be reconstructed, and the linear stability of a given eigenmode can be determined. The description is shown to correctly determine the linear stability of a 150 Hz vortex-driven marginal amplitude instability in a laboratory-scale dump combustor with local and global Rayleigh indices within 16% of the experimentally obtained values. The approach opens up the possibility of predicting modal stability in the future without experiments, by using other forms of data, such as computational data on time-averaged heat release distribution and physics-based modeling data on phase-specific heat release rates.