Vaneless diffuser for low flow rate centrifugal compressor stage

Authors

Olga Solovyeva - Peter the Great St.Petersburg Polytechnic University R&D Laboratory “Gas dynamics of turbo machines”
Yuri Galerkin - Peter the Great St.Petersburg Polytechnic University R&D Laboratory “Gas dynamics of turbo machines”
Aleksandr Drozdov - Peter the Great St.Petersburg Polytechnic University R&D Laboratory “Gas dynamics of turbo machines”

Abstract

Experiments and CFD-analysis of vaneless diffusers demonstrate that in wide range of relative width there is a risk of flow separation at design flow rate as a flow angle after an impeller is too small. To avoid it the inlet part of a diffuser is made with decreasing width along radius. By the elementwise calculation the diffuser with relative width about 2%, narrowed initial part and conical surfaces with the divergence angle 30 between them is turned out to be the best variant of the considered.The diffuser within the stage with narrowed initial part and zero divergence angle has the highest efficiency when relative flow rates are less than design regime flow rate. The stage with diffuser with walls divergence angle 0045’ after narrowed part is less effective on 0.5% when relative flow rates are less than design regime. The maximum efficiency of this stage is 1.5% higher and efficiency is sufficiently higher at big flow rates.