Patent ID: 8172516

Claim:
A variable geometry turbine comprising a turbine wheel supported in a housing for rotation about an axis, an axially movable annular wall member mounted within a cavity provided within the housing, an annular inlet passageway extending radially inwards towards the turbine wheel and defined between a radial face of the movable wall member and an opposing wall of the housing, the movable wall member being axially movable relative to the housing to vary the axial width of the inlet passageway, an array of inlet guide vanes extending between the radial face and an opposing wall defining a radial vane passage, a first circumferential array of apertures provided through said radial face, each of said first array of apertures lying substantially within the vane passage, and a second circumferential array of apertures provided through said radial face, each of said second array of apertures lying substantially upstream or downstream of said first array of apertures relative to the direction of flow through the inlet, such that the inlet and said cavity are in fluid communication via both the first and second sets of apertures, wherein the total area of the second array of apertures is less than the total area of the first array of apertures by virtue of the second array of apertures having apertures that are substantially different from the first array of apertures in at least one of size, shape, and number.