Boundary Layer Effects on the Transonic Flow in a Straight Turbine Cascade

Abstract

The analysis presented here deals with two subjects related to the transonic flow in a straight turbine cascade: 1) turbulization of the suction side boundary layer and its subsequent development along the profile 2) influence of side wall boundary layers on cascade flows. The turbulization effect of supersonic compression on the boundary layers which accompany transonic expansion on the suction side of the profile is investigated by independent methods. Both the experimental results and the calculation confirm the loss of stability of the laminar boundary layer and its subsequent transition into turbulence in the region of an adverse pressure gradient. Also the possibility of reverse transition of turbulent boundary layer in a subsequent strong favourable pressure gradient is investigated. The contraction effect of the wind tunnel side wall boundary layers is expressed by means of the AVDR factor over a wide range of flow regimes determined by the incidence angle and the Mach number. A correction of the exit flow angle from the cascade is made to obtain a purely 2D flow although it is apparent that the measured exit angle values and the exit angle obtained for a 2D flow differ considerably.