Noise mechanisms in a transonic high-pressure turbine stage

Abstract

In modern ultra-high by-pass ratio turboengines, the noise contribution of both turbine stages and combustion chamber is expected to increase drastically. In the present work, both noise sources are evaluated in the realistic, fully three-dimensional transonic high-pressure turbine stage MT1 using large-eddy simulations (LES). An analysis of the basic flow field and the different turbine noise generation mechanisms is performed for two configurations: one with a steady inflow and one with an unsteady inflow, where a plane entropy wave train at a given frequency is injected at the inlet and propagates across the stage generating indirect noise. The noise is evaluated through Fourier analysis, dynamic mode decomposition of the flow field, and estimates of propagation coefficients. The steady case show three different dominant noise mechanisms: the usual stator wake brushing of the rotor blades, the several pulsating shocks in the stage and the vortex shedding. The forced results have additional tonal noise caused by the indirect noise mechanism generated by the acceleration and distortion of entropy spots. They are compared with previous two-dimensional (2D) simulations of a similar stator/rotor configuration, as well as with the compact theory. Results show that the upstream propagating entropy noise is reduced due to the choked turbine nozzle guide vane. Downstream acoustic waves are found to be of similar strength as the 2D case and larger than the blade passing frequency of the wake-interaction mechanism, highlighting the potential impact of indirect combustion noise on the overall noise signature of the engine.