Analyses of flow structure through radial turbine twin-entry volute under pulsatile flows

摘要

In turbocharging applications, twin-entry radial turbines will better use the energy of pulsating exhaust gas flows by avoiding expansion losses into exhaust manifolds and interference between exhaust pulses. In the present study, the flow structure through a twin-entry volute is investigated, by means of code ANSYS-CFX, under the engine-like conditions to have a better insight into the unsteady flow behavior and effects of pulsating gas flows. The unsteady boundary conditions imposed at the inlet and outlet of this radial turbine are related to the engine real operating environment, which were combined from average and instantaneous experimental data. The obtained results show that the flow in the spiral part of twin-entry volute is subject to centrifugal forces which induce a secondary flow in the form of counter-rotating vortices. Also, there is a typical dissymmetrical behaviour characterized by high non-uniformities at the rotor inlet in both spanwise and circumferential directions. The flow incidence at rotor inlet is highly affected circumferentially around the tongue due to interactions between the main flow and that infiltrating to feed the rotor, hence generating extra mixing losses. On the other hand, in the spanwise direction, the flow is affected by the Dean vortices formed within the hub side. The swirling flow motion is only seen at the hub entry side and convected from the outer wall to the rotor entry, and then leaves the volute before a circumferential position of 180 deg from the tongue.