Numerical Modelling of Wake-Jet Interaction with Application to Active Noise Control in Turbomachinery

Abstract

Recent experimental work conducted at the German Aerospace Center (DLR) in cooperation with the Technical University of Berlin (TUB) has demonstrated the feasibility of using artificially induced aerodynamic noise sources to generate the secondary (anti-phase) sound field for the active control of tonal noise in axial turbomachinery. One strategy to realize this approach is to disturb the primary flow in the blade tip regions using high-speed air jets located in the casing wall. In the present study the noise generation mechanisms in such a configuration are investigated. Time-accurate numerical simulations using a short-time Reynolds Averaged Navier-Stokes flow solver are performed for a low-speed high-pressure axial fan with and without air injection. To mitigate spurious reflections along external domain boundaries, time-accurate implicit non-reflecting boundary conditions are developed and described in detail. A single jet per blade passage, located aft of the rotor trailing edge, is considered with a prescribed constant mass flow rate for the active control of the dominant plane wave at the blade passing frequency. The analysis focuses on the three-dimensional interaction between the jet and the rotor flow field. The jet flow field is characterized by the formation of a pair of counter-rotating vortices that persist far downstream of the injection nozzle. For the configurations investigated potential flow field interaction eects are shown to play a decisive role in the noise generation process.