Large eddy simulation of unsteady flows in turbomachinery

Abstract

Unsteady computations of flows through a rotor of turbomachinery are very essential, and another challenge is to predict performances at off-design points, and to provide information on source fields as an input to the Ffowcs Williams-Hawkings (FW-H) equation for noise prediction. A deductive dynamic SGS modelling in large eddy simulation (LES) is proposed that does not impose averaging of the SGS model coefficients in homogeneous directions. This approach is tested and applied to the unsteady simulation of turbomachinery flow. The LES results from three typical cases of unsteady flows in turbomachinery, namely a NACA0018 airfoil, a compressor cascade and an axial fan, are reported. The flow characteristics on and around a symmetrical NACA0018 airfoil at moderate Reynolds number are simulated to establish the mechanism of discrete tone noise by unsteady flows near the trailing edge (TE) of the airfoil in a uniform flow. The flow past a compressor blade cascade is simulated to predict aerodynamic losses and self-noise by unsteady flows at off-design points. As a third example, the flowfields around rotating fan blades are simulated and used as an input to the FW-H equation to predict their farfield noise, which is in good agreement with experimental data.