Investigation of the Interaction Between Tip Leakage and Main Annulus Flow in the Large Scale Turbine Rig: Comparison of Different Rotor Tip Geometries

Shroudless rotor blades are state-of-the-art in modern high pressure turbines. Tip leakage flow has a crucial impact on turbine efficiency. Specific blade tip designs are a key factor to handle tip leakage losses by controlling tip leakage flow and its re-entry into the rotor passage. Comparative measurements of a cavity squealer type tip and a notch type tip have been conducted at the Large Scale Turbine Rig at Technical University of Darmstadt. The test rig has been operated at the blade tips design point. Experimental data have been acquired at rotor inlet and outlet as well as within the rotor passage. For cavity squealer tips, a tip leakage vortex develops at the suction side as the tip leakage flow is rolled-up and further mixed with main annulus flow. The tip leakage vortex determines the blockage of main annulus flow at the blade tip. The design of the suction side of the notch tip benefits a jet-like re-entry of tip leakage flow into the passage. Results are a tip leakage vortex system with smaller sized vortices and a more homogeneous mass flow redistribution in the outer annulus of the rotor. The zone of affected main annulus flow at the blade tip increases through the dominant tip leakage jet.