Unsteady Heat Transfer Topics in Gas Turbine Stages Simulations

Abstract

High pressure gas turbine stages are nowadays working under very challenging conditions. An usual HP stage design is based on transonic highly loaded blades cooled through impingement and film cooling techniques. An important research field for such type of turbine stages is presently represented by the investigation of unsteady performances for loss reduction and heat transfer optimization. Two special issues related to the unsteady stage interaction are addressed in the present work: the first concerns the casing/tip leakage flow, the second the effect and redistribution of inlet temperature hot-spots. The investigation of both requires unsteady modeling since these phenomena are mostly driven by the rotor-stator interaction. High temperature spots, for example, travel through the stator vane as a “hot streaks” of fluid that is mainly redistributed and steered: a simple model of this process is known as Kerrebrock and Mikolajczak’s “segregation effect”. A series of steady and unsteady simulations have been made on the HP MT1 turbine stage test rig of QinetiQ. Given an inlet uniform total pressure field, three different total temperature distributions have been simulated. The first is a uniform reference distribution of total temperature, while the other two non-uniform distributions have been obtained from experimental data with a different alignment with respect to the NGV leading edge. The numerical results have been compared with the experimental values provided by QinetiQ. The comparisons have been discussed focusing on the rotor blade and casing unsteady pressure and heat transfer rate.