Fundamental Mechanism of Entropy Noise in Aero-Engines: Numerical Simulation Available to Purchase

Entropy noise is generated by entropy non-uniformities being accelerated for example in the turbine section downstream of gas-turbine combustion chambers. The entropy noise was experimentally investigated in the test facility Entropy Wave Generator (EWG) [1, 2]. The EWG induces entropy waves by supplying energy pulses to a tube flow. The air stream is accelerated in a convergent-divergent nozzle where entropy noise is excited. In order to investigate entropy noise generation mechanism the numerical simulation of thermo-acoustics was done. This paper shows results concerning the numerical simulation of a reference test case of the EWG applying a compressible URANS approach. The simulations indicate that both fully reflective and non-reflective boundary conditions are inappropriate for modeling of the propagation of entropy noise in this case. The change of cross sectional area in the downstream tube section at a certain position requires the application of a partially reflective boundary condition in the numerical simulation. The variation of the length of the tube section upstream the nozzle proves the existence of entropy noise. Changing the tube length downstream the nozzle results in a phase shift of the superposed downstream and partially reflected upstream propagating pressure fluctuations. Furthermore, the influence of the amount of energy supplied to the system on the generated entropy noise is shown. All numerical results show a good agreement with experimental data.