The effects of tip gap variation on transonic turbine blade tip leakage flow based on VLES approach

Transonic turbine blade Over-Tip Leakage (OTL) flow has significant effects on turbine efficiency and blade thermal load. At present, most of the numerical studies on OTL flow are based on Reynolds-Averaged Navier-Stokes (RANS) method. However, it is difficult to characterize the physical mechanisms of transonic OTL flow accurately due to the inherent shortcomings of RANS method, especially for the unsteady characteristics. To understand the underlying loss mechanisms and aerothermal characteristics of the transonic OTL flow with tip gap variations, the present study applies a Very Large Eddy Simulation (VLES) method based on Wilcox k–ω model to study a transonic cascade OTL flow. The feasibility and accuracy of the VLES turbulence model in OTL flow simulations are confirmed by numerical assessments comparison with the experimental results. The detailed flow structure and its effect on the losses of tip leakage flow are studied for different cases with varying tip gap heights. It is observed that the flow structures including separation vortex and shock waves in the gap become more complex with increasing the tip gap. The mass flow rate, pressure loss, entropy generation, and aerothermal performance for different tip gap heights are further discussed.