Numerical investigation on film cooling performance and unsteady flow dynamics of the trailing edge cutback in a transonic turbine

With the continuous increase in turbine inlet temperature for advanced aero-engines, effective thermal protection of the trailing edge becomes crucial under transonic flow conditions. This study numerically investigates film cooling mechanisms in the trailing edge cutback region of a transonic turbine guide vane. Steady simulations using the SST k-ω turbulence model and unsteady simulations with the Stress-Blended Eddy Simulation (SBES) approach are performed to analyze flow dynamics and heat transfer. The interaction between the mainstream and coolant is shown to significantly affect the formation of recirculation zones and vortex shedding near the wall, which directly impacts coolant coverage and overall cooling effectiveness. Results show that increasing the mainstream Mach number intensifies shear mixing and degrades film cooling effectiveness by up to 9.20 %. At lower mass flow rate, coolant lift-off and weakened wall attachment are observed, leading to a reduction in thermal protection. The SBES simulations reveal that under higher Mach, vortex fragmentation and turbulent dissipation are enhanced. The simulations capture the unsteady evolution of multiscale vortex structures in the high-velocity shear layer between the transonic mainstream and coolant jet, including the evolution of Kelvin-Helmholtz (K–H) vortices and their role in film breakup and entrainment. Moreover, the periodic shedding of coherent vortices in the mixing and wake regions is found to be closely linked to the degradation of cooling performance. This study provides new insights into the complex coolant–mainstream interaction mechanisms in transonic film cooling, offering a physical basis for optimizing cooling designs for highly loaded turbine applications.