Gas turbine engine active clearance control

Abstract

An active clearance control system utilizes a working fluid stream to control radial thermal growth and thereby a clearance between turbine blades and a corresponding shroud of a gas turbine engine. Conduits disposed about a turbine case and proximate to pads defined within the turbine case include a flow surface parallel to the pads. The pads are an area of increased thickness in the turbine case that receives impingement flow from the conduits. Grooves within the pads further increase impingement cooling flow effectiveness. The increased thickness of the pads provides the thermal mass desired to effect thermal expansion and contraction responsive to the cooling airflow.

1 . An active clearance control system for a gas turbine engine, the system comprising:
 a turbine case disposed about an axis including at least one pad encircling the turbine case, the at least one pad substantially parallel to an outer surface of the turbine case; and   a conduit circumferentially encircling the turbine case and the at least one pad, the conduit including a flow surface parallel to and spaced apart from the at least one pad, the flow surface including impingement openings for directing a flow stream onto the at least one pad for controlling a clearance.   
     
     
         2 . The active clearance control system as recited in  claim 1 , wherein the turbine case includes a first thickness and the at least one pad comprises a second thickness greater than the first thickness. 
     
     
         3 . The active clearance control system as recited in  claim 2 , wherein the second thickness extends for an axial distance equal to or less then the flow surface of the conduit. 
     
     
         4 . The active clearance control system as recited in  claim 1 , wherein the at least one pad includes axially orientated grooves for guiding impingement airflow. 
     
     
         5 . The active clearance control system as recited in  claim 4 , wherein the axially orientated grooves provide an increased area of the corresponding pad to increase impingement cooling. 
     
     
         6 . The active clearance control system as recited in  claim 1 , including an inlet communicating the flow stream into the conduit, wherein an opening area of the impingement openings increases in a direction away from the inlet. 
     
     
         7 . The active clearance control system as recited in  claim 6 , wherein a size of each of the impingement openings increases in a direction away from the inlet. 
     
     
         8 . The active clearance control system as recited in  claim 6 , wherein a number of impingement openings for a defined area increases in a direction away from the inlet. 
     
     
         9 . The active clearance control system as recited in  claim 1 , including at least one turbine rotor rotatable about the axis within the turbine case and the at least one pad comprises at least one pad corresponding with each of the at least one turbine rotors. 
     
     
         10 . The active clearance control system as recited in  claim 1 , wherein the conduit comprises a substantially rectangular cross-section. 
     
     
         11 . The active clearance control as recited in  claim 1 , wherein the conduit comprises a first portion extending a first circumferential distance about the turbine case and a second portion extending a second circumferential distance about the turbine case. 
     
     
         12 . The active clearance control as recited in  claim 11 , wherein each of the first portion and second portion are in fluid communication with a common inlet. 
     
     
         13 . The active clearance control as recited in  claim 1 , wherein the flow surface of the conduit is spaced apart a fixed distance common over an entire axial distance of the at least one pad. 
     
     
         14 . The active clearance control as recited in  claim 1 , including a blade shroud disposed radially outward of a turbine blade, wherein the controlled radial growth of the turbine case controls a clearance between the blade shroud and a tip of the turbine blade. 
     
     
         15 . The active clearance control as recited in  claim 1 , wherein the at least one pad comprises at least two pads and the conduit includes an axial length that extends over the at least two pads. 
     
     
         16 . The active clearance control as recited in  claim 1 , wherein the conduit defines a flow area determined to provide a substantially equal airflow through each of the impingement openings. 
     
     
         17 . A method of actively controlling clearances within a gas turbine engine comprising:
 providing a case including a pad of a thickness greater than surrounding portions of the case, the pad encircling the case and extending substantially parallel to a surface of the case;   providing a conduit encircling the pad and spaced circumferentially apart from the pad a defined distance along an axial length of the conduit; and   flowing a working fluid through the conduit and a plurality of impingement openings onto the pad; and   controlling thermal growth of the case by adjusting a temperature of the working fluid flowing onto the pad.   
     
     
         18 . The method of actively controlling clearances within a gas turbine engine as recited in  claim 17 , wherein the case comprises a turbine case that supports a shroud movable responsive to the controlled thermal growth of the turbine case and defining a clearance between the shroud and a tip of a turbine blade by controlling thermal growth of the turbine case. 
     
     
         19 . The method of actively controlling clearances within a gas turbine engine as recited in  claim 17 , including uniformly controlling thermal growth about a circumference of the case. 
     
     
         20 . The method of actively controlling clearances within a gas turbine engine as recited in  claim 17 , wherein the conduit includes a flow surface that is substantially parallel to the case and the pad, the impingement openings disposed within the flow surface.