Numerical Investigations of the Aerothermal Performance of Modern Turbine Blade Tip Geometries at Design and Off-Design Conditions and Under Stationary and Moving Shroud

Abstract

High-pressure turbine blade tips operate under extreme thermal stress, generating significant aerodynamic losses that must be continually optimized to improve engine efficiency and durability. This study uses computational fluid dynamics (CFD) to investigate the aerodynamic and thermal behavior of advanced turbine blade tip configurations, specifically GE's vertical and inclined shelf tips, under both design and off-design transonic conditions. Conventional designs, such as flat and squealer tips, were also analyzed for comparison. Shroud motion effects were included to simulate turbine stage rotation. The simulations are performed by solving the three-dimensional, steady and turbulent form of the Reynolds-Averaged Navier-Stokes (RANS) equations using the Ansys-CFX. A two-equation turbulence model, Shear stress transport (SST) with Gamma-Theta transition formulation is used. CFD results showed strong alignment with experimental data, validated through isentropic Mach number and heat flux measurements. The results revealed that cavity-based designs (squealer and shelf tips) exhibited complex secondary flow structures within the tip cavity, including the formation of suction-side and pressure-side cavity vortices (SSCV and PSCV), which contribute to the tip leakage vortex (TLV) and associated aerodynamic losses. The vertical shelf tip demonstrated the lowest leakage rate in both stationary and moving conditions, attributed to its narrow cavity width and reduced PSCV size, while the inclined shelf exhibited the highest heat transfer coefficient (HTC), beneficial for cooling applications but paired with higher leakage and mixing losses. Notably, these findings differ from previous results on GE's shelf tip, where the inclined shelf had the lowest leakage rate.