Numerical investigation of non-axisymmetric end wall contouring effects in a low-speed compressor tandem stator

Abstract

The present paper reports about a numerical investigation on the effects of non-axisymmetric endwall contouring on a low-speed compressor tandem stator. Usually related to a stochastic or meta-heuristic optimization approach, this technique reserves still several unknowns regarding its global applicability and general effectiveness, in particular concerning its application to compressor stages. The scope of this paper is to provide clarity over fundamental effects of nonaxisymmetric endwall contouring on tandem configurations, in order derive some fundamental guidelines to be used in future contouring definition and tandem stator aerodynamic design. The reference geometry used in this research is a standard tandem vane arrangement with smooth endwall and designed to represent a datum stage configuration for future investigations of such blade geometries, experimental work on a low-speed research compressor being a next step. This paper reports about a thorough flow field analysis of the optimized geometry in order to understand local mechanisms occurring with non-axisymmetric contouring in the tandem stator passage flow field and its overall performance. An improvement of 0.7% polytropic stage efficiency was identified at near stall condition. Furthermore, characteristics of reference and contoured geometry are compared at design and off-design conditions. One key interaction of the endwall contouring with the tandem stator passage flow field has been identified as origin of major flow field improvement at hub and shroud: the reduction of the cross-passage flow, which results in reduction of the strength of the passage vortex and of the hub corner separation on both blades. The paper concludes with some guidelines to derive on how endwall contouring can be most effectively applied in tandem vanes of low-speed compressor stages.