Fluid recirculation turbine system

A turbine configured to receive a pressurized exhaust gas stream, and to convert its total energy into mechanical kinetic energy, comprising:

• a housing forming a scroll directing the exhaust gas stream inward toward an axis of rotor rotation;
• a rotor rotatably mounted within the turbocharger housing to rotate around the axis of rotor rotation, the rotor including a radially directed turbine wheel and a shaft extending along the axis of rotor rotation, the shaft connecting the turbine wheel to bearings within a portion of the housing, wherein the turbine wheel is configured with a hub and a plurality of turbine blades, wherein the hub defines a blade-side surface, and wherein the turbine hub forms an axially-extending wheel gap radially between the blade-side surface and the housing that allows a small amount of flow between inlet exhaust gas and the area behind the hub;
• wherein the turbine hub defines a turbine-wheel back-disk surface facing the housing, and the housing defines a turbine-end wall having an outer surface facing the turbine hub, a turbine-wheel back-disk cavity being defined between the turbine-wheel back-disk surface and the turbine-end-wall outer surface;
• wherein the turbine hub forms a ring-shaped primary axial protrusion extending circularly around the turbine-wheel back-disk surface into a circular channel in the housing, separating the back-disk surface into an outer back-disk surface region and an inner back-disk surface region, and separating the turbine-wheel back-disk cavity into an outer back-disk cavity and an inner back-disk cavity;
• and
• wherein the circular channel leads into a bypass that bypasses the turbine blades.