Effect of Clocking on Entropy Noise Generation Within an Aeronautical High Pressure Turbine Stage

The article reports a detailed experimental and numerical study of the clocking effect between entropy wave spot and stator row on the entropy wave evolution and the indirect noise generation within a high pressure turbine stage. Experimental campaigns considering burner-representative temperature fluctuations injected upstream of an uncooled high-pressure gas turbine stage have been performed in the high-speed closed-loop test rig of the Fluid Machine Laboratory (LFM) of the Politecnico di Milano (Italy). Acoustic measurements focused on entropy noise generation have been carried out by German Aerospace Center, DLR (Germany) with a custom procedure. URANS CFD simulations with and without entropy fluctuations imposed at the stage inlet were performed with the TRAF code, developed by the Università degli Studi di Firenze (Italy). A numerical post-processing procedure, based on the discrete Fourier transform (DFT) of the conservative variables, has been implemented to extract the low-frequency content connected to the entropy fluctuations and indirect noise emissions. Simulations show an overall good agreement with the experiments, especially at the stage outlet thus confirming the possibility to predict entropy noise by means of URANS simulations. By exploiting the combination of experiments and simulations, the evolution of the entropy wave, the identification of the main sources of entropy noise, and the evaluation of indirect noise emissions, for the different clocking positions were properly assessed. Such simulations can be thus used by the designers for parametric studies concerning the clocking position of the perturbation source to reduce the turbine-conbustor interactions and the indirect noise emission with the aim to achieve a design optimization of geometric coupling of a combustor system with a turbine stage.