The Design of Curved Endwall with Leading-edge Deformation

Zhang Xuyang

doi:10.11648/j.ijepe.20200901.11

Abstract

The inlet boundary layer separates in front of the leading edge of the blade on the endwall and forms the pressure side leg of horseshoe vortex and the suction side one. The pressure side leg of the horseshoe vortex immediately moves toward to the suction side and form a stronger vortex, ”passage vortex”, in the cascade. These vortices mentioned above are called secondary flows which will result in an increase of secondary flow losses and a reduction of stage efficiency. In this paper, the flow characteristics are analyzed in the leading edge region and inside the cascade based on the numerical simulation results of the Langston cascade. A new type endwall design method, curved endwall structure combined with the deformation in the leading edge region, is established and optimized. It can be observed that the new structure can efficiently reduce the strength of the horseshoe vortex and suppress the generation of the leading edge separation line and saddle point. The uses of the new structure also decrease the pressure gradient between the pressure side and the suction side in the streamline direction, which suppresses the deviation of the pressure side horseshoe vortex from the pressure side of the endwall to the suction side and delays the formation position of the passage vortex. The rate of increase in the total pressure loss coefficient along the mainstream direction also decreases 25.34% in the exit of the cascade.

Highlights

The inlet boundary layer separates in front of the leading edge of the blade on the endwall and forms the pressure side leg of horseshoe vortex and the suction side one
The use of the curved endwall will reduce the pressure gradient between the pressure side and the suction side of the endwall, which will efficiently suppressing the deflection of the horseshoe vortex on the pressure side leg of horseshoe vortex to the suction side and delay the formation of the passage vortex
The non-uniform rational B-spline surfaces (NURBS) is used for the endwall deformation in the leading edge position of the endwall based on the model with curved endwall

Summary

Introduction

The inlet boundary layer separates in front of the leading edge of the blade on the endwall and forms the pressure side leg of horseshoe vortex and the suction side one. The pressure side leg of the horseshoe vortex immediately moves toward to the suction side and form a stronger vortex, ”passage vortex”, in the cascade These vortices mentioned above are called secondary flows which will result in an increase of secondary flow losses and a reduction of stage efficiency. Between actual endwall flow and the inviscid midspan flow At the exit plane, HPV gets merged with HSV and forms a forms a vortex above the endwall It moves through, entrains passage vortex (PV). Geometries of blade hub section including airfoil and hub the exit flow angle in the endwall region is over or under surface, which intends to alleviate the BTB pressure gradient turned, which generates an extra incidence loss on the so as to low the strength of the PV. Langston [2], Goldstein [3] and Wang et al [4] have edge position, a structure which is called fillet are often used

Methods

Results

Conclusion