Optimization of a Vaned Diffuser Geometry for Radial Compressors: Part II — Optimization of a Diffuser Vane Profile in Low Solidity Diffusers

Abstract

In addition to the diffuser parameter study described in part 1 of this paper the influence of diffuser vane profiles on the efficiency and the operating range of a low solidity diffuser has been studied. Ten different diffuser profiles with identical diffuser configuration (12 vanes, σ = 0.7) were numerically compared. Four of them were tested experimentally. The basic diffuser for this investigation was a simple circular are profile of constant thickness with rounded leading and trailing edges. The simplest improvement of the basic diffuser was made with an elliptical leading edge. The ellipses of different k values (k = 2, 4, 8) were examined. In addition to circular are diffusers with constant thickness, six fully profiled diffusers with non-constant thickness along the camber line were investigated. Four of them are conformably transformed NACA profiles. The results show that the diffuser vane profile does not influence the choke of a stage significantly. The choke point is predominantly influenced by the diffuser’s effective throat size, which was kept nearly constant for all investigated diffusers. Near surge the flow field is difficult to predict so that the optimization of a diffuser vane profile does not necessarily result in an improvement of the diffuser performance.