THE EFFECT OF PURGE AIR ON THE AERODYNAMIC PERFORMANCE OF A STATE-OF-THE-ART TURBINE-REAR-FRAME GUIDE VANE

It is well known that the total pressure ratio and the turbine inlet temperature need to be increased to raise the thermal efficiency of a turbine stage. Therefore, a high exit gas temperature of the combustion chamber is essential to increase the thermal efficiency of aero engines. Consequently, the fluid temperature at the inlet of the Turbine Rear Frame (TRF) rises, too. Without any countermeasures, too hot fluid can enter the cavities between stationary and rotating parts through axial gaps causing damage to structural parts. To prevent such ingression of hot fluid, cold purge air is blown out of the cavities and hence interacts with the main flow of the low-pressure turbine. The present paper investigates the effect of purge air on the aerodynamic performance of a state-of-the-art Turbine Exit Guide-Vane (TEGV) design. For this purpose, five-hole-probe data for three different purge-air flow rates are compared at the inlet and the exit plane of a scaled full annular TEGV cascade. It was found that purge air migrates along the hub end wall toward one TEGV suction side, corresponding to the cross-flow pressure gradient, where it accumulates. The accumulated purge air curls into one vortex. The influence of three TEGV incidence angles, high-negative and high-positive values, is discussed for the nominal purge condition. The investigation was conducted at the Institute of Thermal Turbomachinery and Machine Dynamics of the Graz University of Technology.