A Stall Margin Design Method for Planar and Axisymmetric Diffusers

Abstract

An inverse design method is presented which gives the user control over stall margin, or distance from detachment, along the walls of planar and axisymmetric diffusers. It is proposed that optimum diffuser designs have continuous incipient detachment along their wall boundary layers. This hypothesis is supported by experimental and computational results plus physical arguments concerning the detachment process. Several computed optimum planar diffuser shapes are presented and discussed. For short diffusers with healthy inlet boundary layers, these optimum shaped wall units can have significantly higher pressure recovery than their straight-wall counterparts (up to 40 percent higher Cp in certain favorable cases). In most cases, however, the gains from wall contouring are small when compared to optimum straight-wall designs. This paper differs from earlier discussion in two ways: (i) it employs an improved physical model and correlation of detachment, and (ii) it uses improved boundary layer procedures based on (i).