A simultaneous use of a leading-edge fillet and a non-axisymmetrically contoured endwall in a turbine stage

Secondary flow minimization is a crucial problem in a turbine passage. In the present paper, three different strategies are investigated to reduce the secondary-flow-related total pressure loss. These are leading-edge fillet, non-axisymmetric endwall contouring, and combining these two approaches. An experimental investigation in a single-stage turbine facility and RANS-based computations are performed to evaluate the designs. The experiments are carried out in the large-scale Axial Flow Turbine Research Facility AFTRF. A reference Flat Insert is installed on the nozzle guide vane passage's hub surface to allow future endwall design implementation during the experimental phase. The stereolithography manufactured reference insert has a constant thickness with a cylindrical shape. This investigation also uses four different leading-edge fillets, and they are attached to cylindrical Flat Insert initially. The same fillets are also attached to a contoured endwall. Simultaneous use of a leading-edge fillet and a non-axisymmetric contoured endwall for secondary flow control is the main objective of this research. Total pressure measurements are taken at the rotor inlet plane with a Kiel probe. The probe traversing is completed along one vane pitch and from 8% to 38% span. The leading-edge fillets effectively managed to weaken the horseshoe vortex occurring in front of the leading-edge. In one of the fillet cases sitting on the Flat Insert, the computational results at the NGV exit showed that the mass-averaged loss value was reduced by 1.31%. Three fillet designs decreased the area-averaged loss with a maximum reduction of 15.06%.