Influence of Slot Blowing Operating Parameters on Shock-Induced Separation in a Low-Pressure Turbine Cascade

A numerical investigation is carried out to assess the effect of actuation parameters on flow field and losses in a transonic low-pressure turbine cascade subject to shock-induced separation. Active flow control is implemented through spanwise uniform steady slot blowing on the suction surface. The effect of slot blowing ratio and injection angle are studied by means of two-dimensional unsteady calculations performed using the in-house solver HybFlow. Slot blowing is studied at different blowing ratios and three injection angles, from 15° to 35° to the wall tangent. Slot blowing reduces separation height, but this does not coincide with loss reduction. Wake total pressure losses actually increase with higher blowing ratios because of the shock strengthening connected with increased passage diffusion. Unsteadiness is enhanced with blowing and the wake spans a larger pitchwise portion. The higher vorticity generated at the lambda shock triple point by the local shear interacts with the wake oscillation, enhancing the loss mechanism connected with the wake mixing and shear between vortices. The penetration of the jet depends on the injection angle but the positive effect of near-wall injection that fills the low-momentum portion of the boundary layer is outweighed by the higher losses connected to the increased shock intensity. The enhanced passage diffusion is independent of the injection angle, confirming that it is entirely a consequence of massflow injection rate.