Modeling of indirect combustion noise through a stator

Abstract

In gas turbines, flow fluctuations generated by the flame are accelerated through the turbine and produce sound that may trigger combustion instabilities when propagating back to the combustor and contributes to community noise when leaving the engine. The development of safe and quiet engines requires fast and reliable models to predict these noise sources. Following the recent theoretical developments of Brind and Pullan (2021), a frequency-dependent analytical model is developed to predict noise scattering as well as entropy- and vorticity-noise production through a 2D stator cascade. The flow is inviscid and subsonic and perturbations are one-dimensional (planar waves). Validations are provided with comparisons to numerical simulations and the sensitivity of the results to input parameters is highlighted. Noise scattering is correctly captured by the model for all the frequencies considered, whereas the agreement is limited to a few hundred Hertz for entropy forcing when shear dispersion is not accounted for analytically. When shear dispersion of the entropy waves is included in the model, entropy-based transfer functions collapse with the numerical results for all the frequencies considered. The model also qualitatively predicts vorticity noise production. This noise comes from the acceleration and deviation of vorticity perturbations by the mean flow upstream of the blade leading edge and its contribution to the global indirect noise is negligible.