The Role of Three-Dimensional Interactions in Fluidic Control of Shock-Induced Separation on a Transonic Turbine Blade

An experimental and numerical investigation is conducted to assess the fluid dynamic mechanisms of control by vortex-generator jets for shock-induced separation in a highly loaded low pressure turbine (LPT) blade. Two- and three-dimensional steady RANS computations are performed to evaluate their ability to reproduce the main features of such a complex flow. The test blade is part of a compressible LPT cascade that exhibits shock-induced separation at an exit Mach number of 0.8. Active flow control is implemented through a spanwise row of discrete vortex-generator jets (VGJs) located on the suction surface. The control performance of VGJs in these transonic conditions has an optimum blowing ratio beyond which losses increase. Three-dimensionalities in the flow field are established by discrete VGJ-boundary layer interaction as suggested by Particle-Image Velocimetry (PIV) acquisitions at different spanwise locations. Blade pressure distributions and wake total pressure losses are acquired to evaluate the control performance and compared with calculations. Two-dimensional numerical investigations by RANS simulations suggest that the effect of increased expansion over the passage is a product of massflow injection only. Three-dimensional RANS results are interrogated to give a more detailed representation of the flow features around the jets, such as the jet vortex dynamics and spanwise modulation of the potential field. The analysis of this experimental and numerical information identifies the mechanisms contributing to the performance of skewed jets for control of shock induced separation in a highly loaded LPT blade. The results provide indications on the accuracy of RANS simulations, identifying the challenges of using RANS (2D or 3D) to solve such complex flows.