Aero-thermal performance of a rotor blade cascade with stator-rotor seal purge flow

The present paper investigates the effects of purge flow from a stator-rotor seal gap on the aerodynamic and thermal performance of a rotor blade cascade. Particular attention is paid to thermal results in the leading edge area that is typically difficult to protect. Experimental tests have been performed on a seven-blade cascade of a high-pressure rotor stage of a real gas turbine at low Mach number (Ma2is=0.3). To simulate the rotational effect in a linear cascade environment, a number of inclined fins have been installed inside the stator-rotor gap, making the coolant flow to exit with the right tangential velocity component. Tests have been carried out at different blowing conditions, with mass flow rate ratios up to 2.0%. Aerodynamic effects of purge flow on secondary flow structures were surveyed by traversing a 5-hole miniaturized pressure probe in a plane 0.08cax downstream of the trailing edge. Film cooling effectiveness distributions on the end wall platform were obtained by using Thermochromic Liquid Crystals technique. Results allowed to investigate the effect of purge flow injection from the upstream gap on the secondary flows development and on the thermal protection capability. Purge flow injection of 1.0% reduced secondary flow losses and was found to effectively protect the front end wall region, up to about 0.5cax downstream of the leading edge. Increasing the purge flow up to 1.5% - 2.0% provided a better thermal protection not only stream wise, but also in the region close to the leading edge because of the weakened washing activity of the horseshoe vortex.