End-Wall Boundary Layers in Axial Compressors

Abstract

Various aspects of an end-wall boundary-layer theory in axial compressors, as formulated originally by Mellor and Wood, are analyzed. This analysis contains three parts. In the first part the original formulation is used with a mainstream flow calculation in order to predict overall performances on a single stage compressor. Comparison with experimental data shows the limitation of the assumption of constant shape factor and skin-friction coefficient. In the second part, through an analysis of existing detailed experimental profiles of flow properties behind blades, empirical values for the coefficients of the theory are deduced. It appears that the skin-friction coefficient takes up unusual high values near the tip of the rotor blades and that the hub boundary layer at the outlet is not collateral. In the last part, the basic equations are reformulated in streamline coordinates. This should allow eventual incorporation of the shape factor variation and the Reynolds number effects as well as the introduction of the wall skewing angle. A modification of the original closure equation is proposed allowing for the noncollateral character of the boundary layer at the blade outlet. The original formulation appears as a limit for low skewing angles.