Numerical Modelling of a Turbocharger Splitter-Vaned Centrifugal Impeller at off-Design Conditions, Part I: Impeller Flow Field

The 3D unsteady flow field in a centrifugal impeller with splitter vanes, due to a downstream static pressure distortion imposed by the volute collector at off-design operations, is analysed by means of numerical modelling. Two cases are examined: one analysing the impeller flow field at higher than nominal mass flows and one at lower than nominal mass flows. The hub streamsurface, where the channel length is longer reacts with smoother changes with respect to the shroud. For both cases, it is demonstrated that the exit static pressure non-uniformity propagates upstream and creates unsteady flow in the channels between the impeller full blades and splitter vanes resulting in changes in incidence, velocity components and relative flow angles. In the higher mass flow case the unsteady phenomena are more pronounced.