Numerical simulation of acoustic and entropy waves propagating through turbine blades

The prediction of the transmission coefficients of acoustic and entropy waves propagating through turbine stages is of great importance when dealing with combustion noise. An analytical model considering the compact row assumption is here used for both fixed and rotating blades, including the propagation of waves between blades. Numerical simulations of a stator-rotor turbine stage using two numerical methods for the rotation of the configuration validate the model within the compact assumption and are used to evaluate its precision at non-zero frequencies. Results show that the acoustic wave is correctly predicted with this model for frequencies up to 2000 Hz. The entropy wave, however, is shown to dissipate at non-zero frequencies due to the 2D distortion of the mean flow, which is caused by the no-slip condition at the blades. It is shown that the dissipation of the entropy wave can be reproduced using a simple model based on the mean flow, matching the numerical results.