Numerical Investigation of the Effects of Tip Clearance and Rotor Cavities on the Performance of a 1.5-Stage High-Work Turbine

Abstract

The paper presents CFD simulations about the effects of tip clearance and rotor cavities on the performance of a 1.5-stage high-work turbine. The experimental test case to which the simulation results are compared is the 1.5-stage unshrouded high-work turbine investigated by Behr et al. [1]. The authors performed the simulations on three homogeneously refined meshes. The results on the three meshes were used to quantify discretisation errors applying Richardson extrapolation. The mesh-related discretisation errors for the mass flow rate, total pressure ratio, and mechanical efficiency were below 0.2 % on the finest mesh. The simulation results agreed well with the experimental data. In particular, the loss topologies induced by the hub and shroud passage vortices and the tip-leakage vortex compared well to the measured contours. The simulations showed a consistent and realistic response to the addition of the rotor cavities, with increased mass flow rates and reduced efficiency, shifting the hub passage vortices upwards. Increasing the tip gap decreased the efficiency and strengthened the tip-leakage vortex; decreasing the tip gap had the opposite effect.