A Low Pressure Turbine With Profiled Endwalls and Purge Flow Operating With a Pressure Side Bubble

Abstract

This paper presents an experimental and computational study of non-axisymmetric rotor endwall profiling in a low pressure turbine. Endwall profiling has been proven to be an effective technique to reduce both turbine blade row losses and the required purge flow. For this work, a rotor with profiled endwalls on both hub and shroud is considered. The rotor tip and hub endwalls have been designed using an automatic numerical optimization that is implemented in an in-house MTU code. The endwall shape is modified up to the platform leading edge. Several levels of purge flow are considered in order to analyze the combined effects of endwall profiling and purge flow. The non-dimensional parameters match real engine conditions. The 2-sensor Fast Response Aerodynamic Probe (FRAP) technique system developed at ETH Zurich is used in this experimental campaign. Time-resolved measurements of the unsteady pressure, temperature and entropy fields between the rotor and stator blade rows are made. For the operating point under investigation, the turbine rotor blades have pressure side separations. The unsteady behavior of the pressure side bubble is studied. Furthermore, the results of unsteady RANS simulations are compared to the measurements and the computations are also used to detail the flow field with particular emphasis on the unsteady purge flow migration and transport mechanisms in the turbine main flow containing a rotor pressure side separation. The profiled endwalls show the beneficial effects of improved measured efficiency at this operating point, together with a reduced sensitivity to purge flow.