Numerical and Experimental Analysis of the Tip Leakage Flow in a Squealer Low-Pressure Turbine Blade for Different Operating Conditions

This study combines experiments and numerical simulations (3D-Reynolds-averaged Navier-Stokes (RANS)) to achieve a deep understanding of the effects induced by varying key parameters affecting tip leakage flow in a highly loaded low-pressure turbine (LPT) rotor blade. Specifically, results for flat tip configurations are compared with a squealer tip geometry for different clearance heights and mass flow ratios simulating coolant flow ejected from the tip. Experimental results map the effects of these parameters on loss generation, while detailed insights into the interaction between the tip vortex and other vortical structures within the passage are discussed through computational fluid dynamic (CFD) simulations. Available experimental data include 2D distributions of total pressure and flow angles measured with a five-hole pressure probe downstream of the cascade for different operating conditions, enabling comparison with numerical simulations. The RANS solver provides visualizations of streamlines developing close to the tip region, offering a clear interpretation of the mechanism by which cross flow motion in the tip region interacts with the pressure gradient to generate the tip leakage vortex. The study explores how these processes vary with tip gap height and different mass flow ratios, providing a comprehensive view on the development of the secondary flow system. Finally, additional simulations with moving endwall are conducted to evaluate the impact of the relative motion between the blade and casing in the current application.