Experimental and numerical investigation of an automotive mixed flow turbocharger turbine under pulsating flow conditions

Abstract

It is commonly known that the turbocharger turbine is still designed using the quasi-steady assumption despite its highly pulsating unsteady working conditions. The positioning of a turbocharger in close proximity to the exhaust valve in order to extract substantial energy ultimately necessitates a thorough investigation regarding its performance under pulsating flow conditions. This thesis presents experimental and numerical work, as well as the design of new advanced stator concept to improve turbine performance under pulsating flow conditions. A cold flow test facility is setup mainly to isolate the effect of pulsating flow conditions and therefore allowing the performance deviation from the quasi-steady approach to be properly recorded and documented. Since experimental data alone is not sufficient for understanding the detailed flow field within the turbocharger turbine stage, a complete 3-D Computational Fluid Dynamics model is developed using commercial software Ansys CFX. The model is validated against experimental data for all steady and pulsating conditions. During pulsating conditions, the incidence angle close to the rotor inlet changed significantly which directly affected the turbine performance. A study on the turbine performance improvement by aggressive reduction of nozzle vanes are conducted and experimentally tested. Results of steady and pulsating conditions suggested that the new vanes arrangement delivered significantly improved performance under both operating conditions especially at 50% speed (equivalent to 30000 rpm). At 80% speed (48000 rpm), the turbine efficiency is either similar or better (up to 8 efficiency point improvement) than the baseline arrangements.