A coupled experimental/numerical analysis for low solidity vaned diffusers performance optimization

The impact of low solidity vaned diffusers (LSVDs) on rotating stall and performance was investigated in an industrial centrifugal stage initially designed with a vaneless diffuser. The activity was based on the coupled use of advanced measurement techniques and 3D fully-viscous computations. Experimental data at the impeller inlet was used as boundary conditions in 3D computations, in order to reproduce actual test working conditions. In previous studies the effectiveness of LSVDs for stall control was shown. In this work attention was focused on the effects of LSVDs on the performance curve. Three diffusers were designed and tested in order to achieve a stage performance curve close to the vaneless one or even better. The parameters changed are incidence at design point and blade deflection (blade exit angle compared with free vortex stream line at design point). The main results of this activity are presented and discussed.