Combining LES of combustion chamber and an actuator disk theory to predict combustion noise in a helicopter engine

Abstract

A method to predict combustion noise in real aero-engines using Large Eddy Simulations (LES) of the combustion chamber coupled with an analytical approach to model the acoustic transmission of acoustic and entropy noise through the turbine stages is described. The proposed strategy is tested by comparing predictions of the computed noise with experimental results obtained for a full helicopter engine with high frequency pressure sensors located in the chamber and in all turbine stages. First, an extensive experimental database is used to localize the acoustic sources responsible for the “core-noise” by a three-sensor technique constituting the reference data against which predictions will be assessed. Second, LES of the combustion chamber for two representative operating points are achieved and discussed. The waves leaving the combustion chamber are extracted from these simulations at the outlet of the chamber, and an analytical method based on actuator disk theory and compact assumptions gives noise levels at the various turbine stages using the waves amplitudes at the chamber outlet. Excellent agreement is found at low frequencies between simulations and engine measurements. These results also confirm the importance of indirect combustion noise (due to entropy waves) generated in a helicopter turboshaft engine for the first time.