Indirect noise generation in a high pressure turbine stage

In order to enhance the insight into core noise generation mechanisms in aero-engines this work investigates the noise generation by accelerated entropy and vorticity fluctuations in a high pressure turbine stage. The experiments are conducted in the high pressure turbine facility at Politecnico di Milano in the framework of the European funded project RECORD (Research on Core Noise Reduction). The entropy and vorticity perturbations are produced by a custom-built injection system. The sound fields up-and downstream of the turbine stage are analyzed by the application of two microphone arrays with more than 200 microphones in total. The results indicate that on the upstream section of the turbine stage the generated noise is potentially dominated by the vorticity noise or the direct noise from the injection system. On the downstream side of the turbine stage a clear linear dependence of the generated entropy sound power from the squared values of the injected temperature fluctuation amplitudes is detected for the different operation conditions. This confirms the basic theoretical understanding of entropy noise generation and gives the opportunity for exploiting this knowledge to full-scale application on aero-engines.