Vibratory Response Characterization of a Radial Turbine Wheel for Automotive Turbocharger Application

Abstract

One of the major challenges in the design and development of a turbine wheel for automotive turbochargers is high cycle fatigue (HCF) due to blade resonant vibrations. This is a result of the design trend towards higher blade loading, thinner blades and higher tip speeds which has led to wheel designs and manufacturing techniques which further accentuate the HCF risk. This paper is directed at investigating the resonant response of a variable geometry radial turbine wheel. Wheel resonant response due to vane count excitation was captured by measuring blade tip timing using the Non-intrusive Stress Measurement System (NSMS). Blade deflections in second mode were measured at various turbine inlet pressures and at various inlet vane openings to study their sensitivity. Time dependent 3D CFD calculations were performed to accurately predict the flow field and hence the blade loading at various operating conditions. A finite element (FE) model of the wheel was created in ANSYS and blade loadings calculated from CFD were transferred to the FE mesh to predict blade vibratory strains. Trends of predicted strains were successfully compared against the blade deflection measurements at different turbine inlet pressures and at different vane openings.