Fluid mechanics of ported shroud centrifugal compressor for vehicular turbocharger applications

Abstract

This thesis presents an investigation of the effects of Ported Shroud (PS) self-recirculating casing treatment used in turbocharger centrifugal compressors for increasing the operable range. Computed results, assessed with experimental measurements on ported and non-ported variants of a representative turbocharger compressor, are used to determine the impact of the PS on the flow field and hence performance. It is shown that the main flow path perceives the PS flow as a combination of flow actuations that include injection and removal of mass flow, and injection of axial momentum and tangential momentum. A computational model in which the presence of the PS is replaced by imposed boundary conditions that reflect the individual flow actuations has thus been formulated and implemented. The removal of a fraction of the inducer mass flow was determined to be the dominant flow actuation in setting the performance of PS compressors. Mass flow removal reduces the flow blockage associated with the impeller tip leakage flow and increases the diffusion in the main flow path. Adding swirl to the injected flow in the direction opposite of the wheel rotation results in an increase of the stagnation pressure ratio and a decrease of the efficiency. The loss generation in the flow path has been defined to rationalize efficiency changes associated with PS operation.