Influence of fillet shapes on secondary flow field in a transonic axial flow turbine stage

Numerical experiments were conducted to investigate the effect of leading edge modifications via fillet shapes near vane/blade-endwall juncture in a transonic environment within the highly loaded high pressure turbine stage. The investigated fillet shapes were designed based on geometric parameters: leading edge radius and included angle. The geometrical modifications were achieved to achieve variation in fillet radii at vane/blade endwall juncture along the stream-wise direction, namely variable fillet and constant fillet. Further their influences were studied in both nozzle guide vane and rotor passage secondary flow field. Computational Fluid Dynamics (CFD) method was used to resolve the flow features inside the turbine passage for planar and fillet cases. The presented data highlight the secondary flow features and their behavior using topological properties of flow field aided with the streamline and iso-contour plots. The flow-field results show a significant reduction in the total pressure losses associated with the horse shoe vortex near the leading edge region as the fillet radii are varied. Overall in both vane and rotor passages, variable fillet outperforms the constant fillet by reducing the penetration length of three-dimensional regimes along its span, mitigating the boundary layer growth and improving the loss coefficients.