Variable geometry turbine

A variable geometry turbine comprising: a housing; a turbine wheel supported in the housing for rotation about a turbine axis; an annular inlet passage upstream of said turbine wheel defined between respective inlet surfaces defined by an annular nozzle ring and a facing annular shroud: the nozzle ring being axial movable to vary the size of the inlet passage; a circumferential array of inlet vanes supported by the nozzle ring and extending across the inlet passage; the shroud covering the opening of a shroud cavity defined by the housing inlet passage and inboard of the shroud, and defining a circumferential array of vane slots, the vane slots and shroud cavity being configured to receive said inlet vanes to accommodate axial movement of the nozzle ring; wherein the annular shroud comprises an outer flange around its radially outer periphery, the outer flange defining a circumferential flange groove for receiving a retaining ring for securing the shroud in the opening of the shroud cavity, the flange groove