Aerodynamic influence of rim seal purge flow injection on the main flow in a 1.5-stage axial turbine with nonaxisymmetric end wall contouring

This paper presents an investigation of the aerodynamic influence of rim seal purge flow injection on the main flow in a 1.5-stage turbine with non-axisymmetric end walls and a bowed stator using experimental flow measurements and unsteady RANS simulations. The study focuses on the secondary vortex structures formed in the rotor passages of the 1.5-stage axial turbine rig. Through performance map measurements, it was found that the efficiency gain of the non-axisymmetric configuration is partially eliminated by the injection of purge flow. Numerical investigations, which are supported by detailed flow measurements with five-hole probes and hot-wire probes, revealed that the injection of purge air flow intensifies vortex structures near the hub, thereby generating additional losses. These resulting vortex structures are highly similar both in the axisymmetric baseline and the non-axisymmetric configuration and are the result of jet-like vortices emerging from the cavity. From these findings, it can be concluded that the non-axisymmetric contour and the bowed stator no longer provides any efficiency benefit near the hub. Only the near the casing, where the flow is not affected by the purge flow, the optimized configuration continues to improve the efficiency of the rig by homogenizing the stator outflow and thus reducing the secondary flow structures in the rotor passages.