Fluid dynamic analysis and design strategies for a deswirler device for the direct measurement of radial turbine isentropic efficiency in experimental test rig

Turbocharging remains a key technology for improving the performance of automotive engines and plays a significant role in reducing fuel consumption, particularly when combined with downsizing and engine hybridization. Experimental information on the steady flow performance of turbochargers remains a crucial requirement for optimizing engine-turbocharger matching. This aspect is even more important referring to turbine efficiency, particularly in a radial inflow turbine used for turbocharging. The isentropic efficiency, which is directly evaluated based on measurements of thermodynamic parameters at the inlet and outlet sections, is affected by significant errors. This inaccuracy is mainly due to the non-uniform distribution of flow field and temperature at the outlet measuring section, which results in incorrect evaluation of the turbine outlet temperature, thus of turbine isentropic efficiency. This paper presents an experimental campaign aimed at evaluating the impact of a specific flow field conditioning device at the turbine outlet, with the goal of obtaining a direct evaluation of the turbine isentropic efficiency. A CFD model, which was validated using experimental data, was developed to better understand the performance of the flow field-conditioning device. Additionally, a simplified theoretical model was proposed to generalize the swirl boundary conditions, without the need to model the turbine. A porous medium was calibrated to simulate the honeycombs of the flow field. An optimization procedure was then integrated into the CFD model to provide design suggestions to improve the performance of the flow field conditioning device.