Effects of Gap Leakage on Fluid Flow in a Contoured Turbine Nozzle Guide Vane

Abstract

Computations were performed to study the three-dimensional flow in a nozzle guide vane with leakage issuing from a narrow gap with a backward-facing step located upstream of the airfoil on each endwall. The nozzle guide vane investigated has one flat and one contoured endwall. For the contoured endwall, two configurations of the same contouring profile were investigated with and without gap leakage. In one configuration, all contouring is upstream of the airfoil passage. In the other, the contouring starts upstream of the airfoil passage and continues through it. Results obtained show that when there is gap leakage, secondary flows are reduced at all endwalls for both nozzle configurations investigated. Without gap leakage, secondary flows are reduced only on the contoured endwall in which the contouring started upstream of the airfoil passage and continued through it. When all of the contouring is located upstream of the airfoil passage, there is considerable hot gas ingestion into the gap at both endwalls. When the contouring starts upstream of the airfoil passage and continues throught it, hot gas ingestion was minimal at the contoured endwall and greatly reduced at the flat endwall. This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy. Effects of turbulence were modeled by the low Reynolds number shear-stress transport k-ω model. Solutions were generated by a cell-centered finite-volume method that uses third-order accurate flux-difference splitting of Roe with limiters and multigrid acceleration of a diagonalized ADI scheme with local time stepping on patched structured grids.