Investigation of mechanisms for separated flow transition control using surface grooves on a high-lift low-pressure turbine profile

Abstract

Abstract

Large-eddy simulation computations were performed to investigate the passive flow control mechanisms for surface groove placed span-wise across a high-lift low-pressure turbine blade to control the separated flow transition. Three cases of grooves at different locations on the suction surface were involved in simulations. Compared with the smooth suction surface, the numerical results show that all grooves are effective to reduce the calculated loss at Reynolds number of 5×10⁴ (based on the inlet conditions and axial chord length), because of the thinning of the boundary layer behind the groove for the groove case with the groove trailing edge front of the separation point, and because of the earlier transition inception promoted for all groove cases. It is suggested that the grooves change the instability prosperities of the velocity profile downstream and cause instability waves predominating the transition process. Upstream movements of the transition inception on the grooved surfaces are the result of changes in the most unstable frequencies and the initial amplitude of instability waves at the most unstable frequencies. The results at Reynolds number of 1×10⁵ suggest that the effect of groove on the location of transition inception is more significant for higher Reynolds numbers. The transition onset can be induced inside the groove at a high Reynolds number, leading to the turbulent boundary-layer-generated loss predominating in the profile loss and the negative effect of the groove appearing.