Aerodynamic and Mechanic Analyses of An Asymmetrically Scalloped Radial Turbine

Abstract

In order to reduce the aerodynamic efficiency loss of deeply scalloped radial turbines, asymmetrically scalloping of turbines’ backdisc has been invented for a number of years. However, the mechanism how this works and its mechanical implication have not been reported in the open literature. In this paper, taking the symmetrically scalloped turbine of a turbocharger for marine generator application as the baseline, two asymmetrically scalloped turbines were developed from it: one with scalloping bias to the pressure side, and the other to the suction side of the blades. Mechanic and aerodynamic analyses of these three turbines were carried out using ANSYS Workbench. The results indicate that the asymmetrically scalloped turbine with scalloping bias to the pressure side can reduce the backdisc-heat shield cavity leakage flow going into the blade suction surface through the scalloped backdisc, due to the influence of the high pressure near the pressure surface of the blade, thus decrease the size of vortices the leakage flow generated near the suction surface inside the blade passages and associated mixing loss. Compared to the symmetrically scalloped turbine, it increases the maximum principal stress by 0.39% and 5.2% at blade fillet and backdisc respectively, but the aerodynamic efficiency of the turbine is increased by 0.78% point at a turbine U/C value of 0.43, and the smaller the value of the U/C is, the greater the efficiency advantage will be. By contrast, the turbine with suction side bias scalloping shows the poorest aerodynamic performance, due to an increased leakage flow through its scalloped backdisc.