Exhaust diffuser for a gas turbine, and method thereof

Abstract

An exhaust diffuser assembly is provided, particularly for a stationary gas turbine. The exhaust diffuser assembly includes a longitudinal axis, a diffuser inlet for receiving a turbine mainflow gas, a diffuser outlet, and a diverging diffuser wall having an adjustable geometry and forming a conduit for flow of the gas therethrough from the diffuser inlet to the diffuser outlet. The diffuser wall has a divergence angle ‘α’ with respect to the longitudinal axis. The diffuser assembly also has a diffuser geometry control device for controlling a recovery of pressure from the gas between the diffuser inlet and the diffuser outlet by adjusting the divergence angle ‘α’ of the diffuser wall to cause a resultant flow field of the gas that is attached to the diffuser wall.

1 - 15 . (canceled) 
     
     
         16 . An exhaust diffuser assembly for a stationary gas turbine, comprising:
 a longitudinal axis,   a diffuser inlet for receiving a turbine mainflow gas,   a diffuser outlet,   a diverging diffuser wall having an adjustable geometry and forming a conduit for flow of the gas therethrough from the diffuser inlet to the diffuser outlet, the diffuser wall having a divergence angle ‘α’ with respect to the longitudinal axis, and   a diffuser geometry control device for controlling a recovery of pressure from the gas between the diffuser inlet and the diffuser outlet by adjusting the divergence angle ‘α’ of the diffuser wall to cause a resultant flow field of the gas that is attached to the diffuser wall.   
     
     
         17 . The diffuser assembly according to  claim 16 , wherein the diffuser geometry control device comprises one or more actuators disposed on a surface the diffuser wall, the one or more actuators being adapted to exert an adjustable pressure the diffuser wall to resultantly adjust the divergence angle ‘α’ of the diffuser wall. 
     
     
         18 . The diffuser assembly according to  claim 17 , wherein the one or more actuators adapted for increasing the divergence angle ‘α’ to cause a resultant flow field beyond a point of flow separation of the gas from the diffuser wall and subsequently reducing the divergence angle ‘α’ to re-attach the flow of the gas to the diffuser wall, so as to cause a resultant flow of the gas through the diffuser wall that is substantially proximate and prior to the point of flow separation. 
     
     
         19 . The diffuser assembly according to  claim 18 , further comprising a pressure probe disposed in a flow path of the gas inside the diffuser wall, wherein the point of flow separation is detected based on a decrease in sensed pressure between two progressively increasing settings of the divergence angle ‘α’. 
     
     
         20 . The diffuser assembly according to  claim 18 , further comprising a sonic probe disposed in a flow path of the gas inside the diffuser wall to detect the point of flow separation. 
     
     
         21 . The diffuser assembly according to  claim 18 , wherein the point of flow separation is determined by a flow visualization device adapted for detecting local direction of flow. 
     
     
         22 . The diffuser assembly according to  claim 16 , wherein the diffuser wall is made of a piece of sheet metal wound to spiral form. 
     
     
         23 . The diffuser assembly according to  claim 16 , wherein the diffuser wall is made from a piece of sheet metal wound into a conical shape, wherein the edges of the piece of sheet metal are slidable against each other. 
     
     
         24 . The diffuser assembly according to  claim 16 , wherein the diffuser wall comprises an adjustable portion having a rectangular cross-section, wherein the diffuser wall at the adjustable portion is flexibly attached to a fixed portion by a hinge. 
     
     
         25 . The diffuser assembly according to  claim 16 , wherein the diffuser wall has a rectangular cross-sectional geometry formed by angular plates forming corners of the rectangle, the angular plates being interspaced by and flat plates over which the angular plates are slidable such that the rectangular cross-sectional shape is adjustable along diagonal directions. 
     
     
         26 . A method for operating an exhaust diffuser for a stationary gas turbine, comprising:
 receiving a turbine mainflow gas at a diffuser inlet,   passing the gas through a diverging diffuser wall having an adjustable geometry defining a conduit for flow the gas between the diffuser inlet and a diffuser outlet, the diffuser wall having a divergence angle ‘α’ with respect to a diffuser longitudinal axis, and   controlling a recovery of pressure from the gas between the diffuser inlet and the diffuser outlet by controlling a geometry of the diffuser wall, the controlling of the geometry comprising adjusting the divergence angle ‘α’ of the diffuser wall to cause a resultant flow field of the gas that is attached to the diffuser wall.   
     
     
         27 . The method according to  claim 26 , wherein controlling the geometry of the diffuser wall comprises disposing one or more actuators on a surface of the diffuser wall and controlling the one or more actuators to exert an adjustable pressure on the diffuser wall to resultantly adjust the divergence angle ‘α’ of the diffuser wall. 
     
     
         28 . The method according to  claim 27 , comprising controlling the one or more actuators to increase the divergence angle ‘α’ to cause a resultant flow field beyond a point of flow separation of the gas from the diffuser wall and subsequently reducing the divergence angle ‘α’ to re-attach the flow of the gas to the diffuser wall, so as to cause a resultant flow of the gas through the diffuser wall that is substantially proximate and prior to the point of flow separation. 
     
     
         29 . The method according to  claim 28 , further comprising disposing a pressure probe in a flow path of the gas inside the diffuser wall, and detecting the point of flow separation based on a decrease in sensed pressure between two progressively increasing settings of the divergence angle ‘α’. 
     
     
         30 . The method according to  claim 28 , further comprising detecting the point of flow separation by a sonic probe disposed in a flow path of the gas inside the diffuser wall.