Analyses of steady and unsteady flows in a turbocharger's radial turbine

This study presents the aerodynamic behaviours of a twin-entry radial inflow turbine under steady and transient conditions. The influence of the volute tongue is depicted by a low momentum wake propagating toward the rotor entry, but its effect does not extend beyond a circumferential position of 60 degrees, and more total pressure loss is revealed with respect to the hub side. The transient simulations carried out at different operating conditions and Fast Fourier Transform analysis of static pressure fluctuations induced by the components' interactions have revealed a space-time periodic behaviour which has been described by a double Fourier decomposition. The flow simulations considering the two sides subject to both non-pulsatile and pulsatile flows conditions have revealed the existing rotor and tongue potential effects and interaction effects the rotor and volute, in addition to the circumferential and spanwise flow non-uniformities at the volute exit, which are more accentuated with a pulsatile flow at inlet. The results of Fast Fourier Transform analysis of temporal pressure fluctuations at the inter-space depict an unsteady behaviour related to the pulsatile frequencies which are characterised by high amplitudes. On the other hand, the spatial pressure fluctuations for the non-pulsatile and pulsatile flows conditions seem to have the same dominant modes since Fast Fourier Transform analysis was carried out at a fixed instant.