Hybrid Large-Eddy Simulation of Tip-Leakage Flow in a 1.5-Stage High Pressure Turbine

In gas turbines, tip-leakage flow (TLF) could account for up to one-third of the total stage loss in the turbine component. This study used hybrid LES-RANS (IDDES) to examine the flow in a 1.5-stage high-pressure turbine under geometric, pressure (P), temperature (T), rotational speed, mass-flow rate, Mach number, and Reynolds number conditions that are relevant to land-based, electric-power-generation gas turbines. Though IDDES was used, 95% of the flow field from the trailing edge of the firststage stator vane to the inlet of the second-stage stator and up to 80% of the tip gap was simulated by LES. Results are presented that show details of the unsteady vortex shedding from the firststage vane, effects of stator-rotor interactions on secondary flows in the blade passage, and the tip-leakage flow structures about the tip-gap region. The unsteadiness in the flow was found to cause the adiabatic-wall temperature and the pressure on the blade surface to vary by as much as 150 K and 0.5 MPa. In addition, the dominant frequency produced by vortex shedding at the trailing edge of the first-stage stator vane was found to be an order of magnitude higher than the frequency from blade passing. Based on the results obtained for the mean flow structures in the tip-gap region, two designs were proposed. One is where transpiration cooling should be implemented. The other is an appendage on the blade tip’s pressure side to reduce the amount of TLF.