Effects of Near-Wall Streamwise Vortex on the Film Cooling Performance of a Fan-Shaped Hole

Fan-shaped hole is a typical shaped hole frequently used in gas turbine film cooling, which may operate in a complex vortical flow environment of turbine blade rows. It is critical to understand the destructive mechanism of the film cooling by near-wall vortex on the endwall surface. A vortex generator (VG) was installed in front of a discrete fan-shaped hole to produce a vortical environment on a flat plate. Heat transfer effects were experimentally studied for mainstream velocities of 20 m/s by measuring the adiabatic film cooling effectiveness at blowing ratios M = 0.5 to 2.5. Fluid dynamics effects of vortical upwash and downwash movements were numerically analyzed. Results show that near-wall streamwise vortex destroys the film flow and intensifies the mixing of hot gas and coolant flow, which leads to the deterioration of film cooling performance. Film coverage area varies remarkably with respect to the positions of streamwise vortex. An efficient blowing ratio has a strong ability to mitigate the influence of near-wall vortex. At M = 2.5, streamwise vortex can restrain liftoff tendency of coolant jet and retard the decrease of film cooling effects.