Spectral POD Analysis of Combustion Noise Emitted by a Non-reacting Combustor Simulator

Abstract

Combustion noise represents an important part of the overall emissions of gas turbines and aerospace engines. For modern lean combustors, there are several relevant physical phenomena which contribute to combustion noise, such as fluctuations of heat release in case of so-called direct combustion noise or acceleration of flow inhomogeneities in case of so-called indirect combustion noise. In order to describe the noise production mechanisms, it remains although difficult to distinguish between the different sources and to quantify the corresponding sound emission using classical approaches based on linear acoustics. This study therefore proposes an alternative method to identify the noise components based on an empirical mode decomposition technique, the so-called Spectral Proper Orthogonal Decomposition (SPOD). Using data extracted from a Large Eddy Simulation of a non-reacting combustor simulator, the suitability of the SPOD to identify the relationship between entropy disturbances due to cooling air entering the combustor and sound production was investigated. The comparison of the coherent structures obtained with the SPOD from entropy and pressure fluctuations clearly evidences similarities in spatial distributions and mode orders as well as energy peaks at similar frequencies. This makes the SPOD a promising approach to identify main features and structures of combustor noise components.