Cooling system and method for an axial flow turbine

Abstract

An axial flow turbine is described having a casing defining a flow path for a working fluid therein, a rotor co-axial to the casing, a plurality of stages, each including a stationary row of vanes circumferentially mounted on the casing a rotating row of blades, circumferentially mounted on the rotor, with an inner face of the casing exposed to the working fluid having one or more essentially circumferential grooves of increasing depth each ending in an extraction port with a bore.

What is claimed is: 
     
         1 . An axial flow turbine comprising:
 a casing defining a flow path for a working fluid therein;   a rotor co-axial to the casing;   a plurality of stages, each comprising:
 a stationary row of vanes circumferentially mounted on the casing; and 
 a rotating row of blades circumferentially mounted on the rotor, 
   wherein an inner face of the casing exposed to the working fluid includes one or more essentially circumferential grooves of increasing depth in the rotational direction of the rotating blades with each groove ending in an extraction port with a bore; and   wherein the one or more grooves ending at a joint line of the casing and bores for the extraction ports are at the opposite sides of the joint line.   
     
     
         2 . The turbine of  claim 1  wherein the bore of the extraction port is oriented tangentially to the groove. 
     
     
         3 . The turbine of  claim 1  having two grooves in diametrically opposing positions along essentially the same circumference. 
     
     
         4 . The turbine of  claim 1  wherein the one or more grooves in conjunction with the extraction ports are adapted to remove working fluid from a volume in the vicinity of the tip of the blades for the purpose of cooling the tips of rotating blades. 
     
     
         5 . The turbine of  claim 1  wherein the extraction ports have valves designed to open or shut depending on the mass flow flowing through the turbine. 
     
     
         6 . The turbine of  claim 1  wherein the one or more grooves in conjunction with the extraction port are located between vanes and blades of the last stage of the turbine. 
     
     
         7 . The turbine of  claim 1  wherein the one or more grooves in conjunction with the extraction port are located in the vicinity of a row of blades that are at least partly made of composite material. 
     
     
         8 . A method of cooling blades in an axial flow turbine having:
 a casing defining a flow path for a working fluid therein;   a rotor co-axial to the casing;   a plurality of stages, each comprising: a stationary row of vanes circumferentially mounted on the casing; and   a rotating row of blades circumferentially mounted on the rotor, with an inner face of the casing exposed to the working fluid including one or more essentially circumferential grooves of increasing depth in the rotational direction of the rotating blades with each groove ending in an extraction port with a bore,   the method including opening the extraction port and extracting working fluid from a volume close to the tips of the blades through the grooves and the extraction port.   
     
     
         9 . The method of  claim 8 , wherein the extraction port is closed during normal operation of the turbine and opened when the turbine operates under low mass flow conditions.