Unsteady winglet-cavity tip on leakage flow in a high-pressure turbine stage of low-aspect ratio

Abstract

In an unshrouded high-pressure turbine, the upstream vane wake, vane–blade interaction and blade tip leakage flow indicate complex and unsteady flow characteristics. Considering a high-pressure turbine stage of low-aspect ratio, the effects of the flat tip, cavity tip and winglet-cavity tip on the unsteady flow characteristics are investigated by numerical simulation. The exit Mach number and Reynolds number based on the chord of vane are 0.9 and 5.5×105, respectively. The pressure ratio of stage is 2.4. The time-resolved results indicate that the winglet-cavity tip scheme has smaller time variation of the total performance parameters and obtains a smaller tip leakage mass flow and a higher turbine stage efficient than the other cases. The vane–rotor interaction affects the pressure distribution at the region of blade leading edge remarkably and leads to a large time variation of tip leakage mass flow at the front of blade tip. The unsteady aerodynamic performance is analyzed with entropy-increase distribution at stage outlet and the vane–rotor interaction is discussed by the entropy-increase phase–time and phase–phase diagrams at blade outlet. Compared with the flat tip and cavity tip, the upper passage vortex loss is reduced obviously by the winglet-cavity tip. Thus, it is evaluated that the improvement of turbine stage coefficient with winglet-cavity tip results from the reduction of the upper passage vortex loss.