Experimental Investigation and Computational Evaluation of Contoured Endwall and Leading Edge Fillet Configurations in a Turbine NGV

Abstract

Secondary flow minimization is a crucial problem in a turbine passage. In the present paper, three different ways are employed to reduce the secondary flow related total pressure loss. These are nonaxisymmetric endwall contouring, leading edge (LE) fillet, and the combination of these two approaches. Experimental investigation and computational assessment are applied for the performance calculations. The experiments are carried out in an annular Axial Flow Turbine Research Facility (AFTRF) having a diameter of 91.66cm. For the experimental measurement comparison, a reference Flat Insert is installed in the nozzle guide vane (NGV) passage. It has a constant thickness with cylindrical surface and is manufactured by stereolithography (SLA) method. Also, Flat Insert has a backward facing step at the NGV exit, and the effect of this step is analyzed computationally. Four different LE fillets are designed, and they are attached to both cylindrical Flat Insert and the contoured endwall. Total pressure measurements are taken at rotor inlet plane with Kiel probe. The probe traversing is completed with one vane pitch and from 8% to 38% span. For one of the designs, area-averaged loss is reduced by 15.06%. The simulation estimated this reduction as 6.95%. Computational evaluation is also performed at the NGV exit plane. The most effective design reduced the mass-averaged loss by 1.84% on the whole passage. The computational study did not include the rim seal flow between the vane and rotor domain and also rotor simulation was absent. The difference between the measurements and the simulation comes from these two important effects.