Computational and Experimental Study of the Unsteady Convection of Entropy Waves Within a High Pressure Turbine Stage

This paper describes the transport and the interaction of entropy waves generated by combustor burners within a HP turbine stage. Experiments and CFD simulations were carried out in the context of the EU Project RECORD. Experimental campaigns considering burner representative temperature fluctuations at the stage inlet have been performed in the test-rig at Politecnico di Milano. The pulsating entropy waves are injected in stream-wise direction at four different azimuthal positions featuring a 7% over-temperature with a frequency of 90 Hz. Detailed time-resolved temperature measurements upstream and downstream of the stage, as well as in the stator–rotor axial gap were performed. Time-accurate CFD simulations with and without entropy fluctuations at the stage inlet were performed with the TRAF code, developed by the University of Florence. A numerical post-processing procedure, based on the DFT of the conservative variables has been implemented to extract the low frequency content connected to the entropy fluctuations. Measurements highlighted a significant attenuation of the entropy wave spot throughout their transport within the stator channel and their interaction with the rotor rows. Simulations show an overall good agreement with the experiments, especially at the stage outlet. By exploiting the combination of experiments and simulations, the aerodynamic and thermal implications of the temperature fluctuation injected upstream were properly assessed, thus suggesting useful information to the designers. The comparison with the experiments confirms the accuracy of the CFD method to solve the periodic low frequency content associated with the entropy wave fluctuation.