Numerical analysis of two-dimensional unsteady turbulent flows in a turbine stage.

Abstract

A numerical technique for the analysis of three-dimensional unsteady turbulent flows in a turbine stage is presented. To calculate the unsteady interaction flow fields in a nozzle and bucket simultaneously, the nozzle outlet elements and the bucket inlet elements are overlapped in the axial direction and are used for unsteady data transfer between flow regions. On the periodic and connecting boundaries, a time phase shift boundary condition is introduced for computations of different blade number between nozzle and bucket. To calculate the flows in arbitrarily shaped geometries, a control volume method combined with a body-fitted curvilinear coordinate system is used to obtain spatially discretized governing equations, while the second-order accurate Adams-Bashforth method is employed for time integration. In the present analysis, a two-equation model of turbulence is introduced to estimate the turbulence effect. In order to assure the effectiveness of the present method, computations are carried out for the flow in a subsonic turbine stage of three different axial distances between nozzle and bucket. It is shown that unsteady flow phenomena such as the nozzle wake and pressure field interactions are well predicted, and the periodic aerodynamic forces acting on the buckets, including the effect of the axial distance difference, are obtained by the present method.