A nonaxisymmetric endwall design approach and its computational assessment in the NGV of an HP turbine stage

Nonaxisymmetric endwall contouring has recently become one of the ways to minimize the secondary flow related losses in a turbine nozzle guide vane (NGV) passage. In this study, a specific nonaxisymmetric endwall contouring design methodology is introduced. Fourier series based splines at different axial locations are generated and combined with the help of streamwise B-Splines within solid modeling program. Eight different contoured endwalls are presented in this paper. Computational study of these designs is performed by the finite-volume flow solver. The SST k-ω turbulence model is selected and a bodyfitted structured grid is used. Total pressure distribution at the NGV exit shows that contouring the endwall effectively changes the results. From among these various designs, the most promising one is with the contouring extended in the upstream of the vane leading edge. Mass-averaged value of 3.2% total pressure loss reduction is achieved at the NGV exit plane. The current study was performed in a rotating turbine rig simulating a state of the art HP turbine stage. An NGV only simulation is performed. This approach is helpful in isolating rotor-stator influence and the possible upstream flow modifications of the rim seal cavity flow existing in the rotating turbine research rig. The investigation including the rotor-stator interaction and rim seal cavity flow is the topic of a subsequent paper currently under progress.