Combined Effects of Surface Trips and Unsteady Wakes on the Boundary Layer Development of an Ultra-High-Lift LP Turbine Blade

An experimental investigation of the combined effects of upstream unsteady wakes and surface trips on the boundary layer development on an ultra-high-lift low-pressure turbine blade, known as T106C, is described. Due to the large adverse pressure gradient, the incoming wakes are not strong enough to periodically suppress the large separation bubble on the smooth suction surface of the T106C blade. Therefore, the profile loss is not reduced as much as might be possible. The first part of this paper concerns the parametric study of the effect of surface trips on the profile losses to optimize the surface trip parameters. The parametric study included the effects of size, type, and location of the surface trips under unsteady flow conditions. The surface trips were straight cylindrical wires, straight rectangular steps, wavy rectangular steps, or wavy cylindrical wires. The second part studies the boundary layer development on the suction surface of the T106C linear cascade blade with and without the recommended surface trips to investigate the loss reduction mechanism. It is found that the selected surface trip does not induce transition immediately, but hastens the transition process in the separated shear layer underneath the wakes and between them. In this way, the combined effects of the surface trip and unsteady wakes further reduce the profile losses. This passive flow control method can be used over a relatively wide range of Reynolds numbers.