Study of the Flow in a Vaneless Diffuser at Part Speed Operating Conditions

Abstract

The aim of the current paper is to investigate the evolution of the flow in the vaneless diffuser of a scaled-up turbocharger compressor, using the steady-state viscous calculations. First, the predicted flow patterns are compared with the detailed LDA and probe measurements, acquired at different operating conditions. Then, the numerical results are analyzed further to understand the origins of the flow features, observed in the measurements. It is shown that despite the complexity of the flow, the main flow features in the vaneless diffuser can be predicted at different operating conditions, using a simple mixing length turbulence model. It is also demonstrated that in the compressor studied, a vortical flow feature develops near the diffuser shroud at high flow coefficients. This flow feature is generated by strong pressure variations downstream of the impeller trailing edge, and disappears at low flow coefficients, where the static pressure gradient becomes almost radial in the vaneless diffuser.