Experimental Work on the Characterization of the Hysteresis Behavior of the Vaned and Vaneless Mixed-Flow Turbocharger Turbine

Abstract

It has been proven that the turbocharger turbine operates differently under unsteady flow conditions as compared to steady flow. Despite this, the turbine wheel is still designed under the assumption of steady flow conditions. This results in overprediction of the efficiency during actual conditions, which are always pulsating because of the reciprocating nature of an internal combustion engine. The difficulties in characterizing turbine behavior under pulsating flow conditions is attributable to complexities in characterizing the mass flow imbalance and its deviation from steady-state conditions. This paper attempts to describe the mass flow hysteresis properties that occur as a result of the filling and emptying phenomena as the flow frequency is increased from 20 to 60 Hz for vaned and vaneless turbine stators. The phenomena, coupled with difficulties in obtaining instantaneous mass flow rate, resulted in a complex experimental arrangement. Results indicated that the hysteresis properties of each frequency differ substantially, depending on the differences of the propagation velocity between the bulk flow and pressure. The hysteresis loop for vaned turbines also seems to have a larger range than its vaneless counterpart.