Oil mist separation in gas turbine engines

Abstract

A rotor stage is provided which comprises a shank passage for separating liquid from secondary air system (SAS) air. The shank passage is formed between a radially outer surface of a disc post, a radially inner surface of one or more blade platforms, and the shanks of two neighbouring blades. In use, SAS air is supplied to the shank passage. Any liquid, such as oil, is separated from the SAS air due to the centripetal acceleration of the rotation of the rotor disc. The separated oil can then flow, or seep, past the blade platform and into the working fluid. The remainder of the SAS air passes through a hole in a sealing plate at the downstream end of the rotor stage, thereby providing SAS air with a lower liquid content for use downstream of the rotor stage.

1 . A rotor stage for a gas turbine engine, the rotor stage having axial, radial and circumferential directions and comprising:
 a rotor disc having a plurality of radially extending disc posts;   a plurality of rotor blades, each rotor blade comprising:
 an attachment portion configured to engage with circumferentially neighbouring disc posts to attach the rotor blade to the rotor disc; 
 a platform from which an aerofoil extends; and 
 a shank extending from the attachment portion to the platform, wherein: 
   the rotor stage further comprises a sealing plate positioned radially inward of the platform and axially downstream of the disc posts and attachment portion, wherein:   the sealing plate comprises at least one shank flow opening located radially inboard and axially downstream of a shank passage formed by the shanks of two neighbouring rotor blades, a radially outer surface of a disc post, and radially inner surfaces of the respective platforms of the two neighbouring blades, the shank flow opening allowing internal flow to pass through the shank passage and the sealing plate to a downstream side of the rotor stage via a tortuous flow path between the shank passage and the shank flow opening such that, in use, any oil passing through the shank passage is centrifuged towards the platforms and thereby separated from the rest of the internal flow.   
     
     
         2 . A rotor stage according to  claim 1 , wherein the or each shank flow opening has an axis that is substantially aligned with the axial direction of the rotor stage. 
     
     
         3 . A rotor stage according to  claim 1 , wherein the tortuous flow path turns from a substantially axial direction in the shank passage, to a substantially radial direction between the shank passage and the shank flow opening, and back to a substantially axial direction to pass through the shank flow opening. 
     
     
         4 . A rotor stage according to  claim 1 , wherein the sealing plate comprises a plurality of shank flow openings, each shank flow opening being configured to allow flow from one or more shank passages to pass therethrough. 
     
     
         5 . A rotor stage according to  claim 1 , wherein the sealing plate comprises at least as many shank flow openings as the number of disc blades in the rotor stage. 
     
     
         6 . A rotor stage according to  claim 1 , wherein the sealing plate is a circumferential sealing plate that extends circumferentially at the downstream side of the rotor stage. 
     
     
         7 . A rotor stage according to  claim 1 , wherein the sealing plate comprises a plurality of sealing plate segments. 
     
     
         8 . A rotor stage according to  claim 1 , wherein the one or more shank flow opening or openings are the only openings provided in the sealing plate, such that the only flow that passes through the sealing plate is from the shank passage. 
     
     
         9 . A rotor stage according to  claim 1 , further comprising a platform opening provided in the platform of a rotor blade and/or between platforms of adjacent rotor blades, the platform opening being configured to allow, in use, oil to pass therethrough into a working gas of the gas turbine engine. 
     
     
         10 . A rotor stage according to  claim 9 , wherein the number of platform openings is the same as the number of rotor blades. 
     
     
         11 . A rotor stage according to  claim 1 , wherein:
 each rotor blade further comprises a cooling flow inlet formed on a radially inner surface of the attachment portion and configured to allow cooling flow to enter into the blade;   a cooling flow supply passage is formed between the radially inner surface of the attachment portion and the rotor disc; and   a downstream end of the cooling flow supply passage is blocked by the sealing plate, such that, in use, substantially all of the fluid that passes through the cooling flow supply passage enters the cooling flow inlet.   
     
     
         12 . A method of separating oil from an internal flow through a rotor stage of a gas turbine engine, the rotor stage having axial, radial and circumferential directions and comprising:
 a rotor disc having a plurality of radially extending disc posts; and   a plurality of rotor blades, each rotor blade comprising: an attachment portion configured to engage with circumferentially neighbouring disc posts to attach the rotor blade to the rotor disc; a platform from which an aerofoil extends; and a shank extending from the attachment portion to the platform,
 the method comprising: 
   passing the internal flow through a shank passage formed by the shanks of two neighbouring rotor blades, a radially outer surface of a disc post, and radially inner surfaces of the respective platforms of the two neighbouring blades and out through a shank flow opening in a sealing plate positioned radially inward of the platform and axially downstream of the disc posts and attachment portion; and   rotating the rotor stage so as to separate the oil from the rest of the internal flow through centripetal action within the shank passage.   
     
     
         13 . A method of separating oil from an internal flow according to  claim 12 , further comprising passing the separated oil through gaps in the platform or between neighbouring platforms into a working fluid of the gas turbine engine. 
     
     
         14 . A method of separating oil from an internal flow according to  claim 12 , wherein the internal flow passes out through the or each shank flow opening in a direction substantially aligned with the axial direction of the rotor stage. 
     
     
         15 . A method of separating oil from an internal flow according to  claim 12 , further comprising passing the internal flow from which the oil has been separated out of the rotor stage through a tortuous path.