Numerical Investigation of the Fundamental Mechanism for Entropy Noise Generation in Aero-Engines

Abstract In the present work, the generation and propagation of entropy noise is computed using a compressible URANS approach in combination with appropriate acoustic boundary conditions. The Entropy Wave Generator (EWG) experiment is best suited for validating the proposed approach and for investigating the acoustic sources of entropy noise. The EWG involves a non-reactive tube flow, where entropy modes are imposed to an incoming air flow by using a heating module. The generated temperature non-uniformities are accelerated with the mean flow downstream in a convergent divergent nozzle, thus producing entropy noise. Simulation results of pressure fluctuations and their spectra for a defined standard configuration as well as for diff erent operating points of the EWG agree very well with the respective experimental data. Additionally, an analysis of the acoustic sources was performed. For this purpose the acoustic sources caused by the acceleration of density inhomogeneities were calculated. For the first time, a numerical method is introduced for the localization of the acoustic sources of entropy noise in acceleration/deceleration regions.