Abstract: Methods and apparatus for controlling the radial clearance between the rotor and stator elements in the turbine section of a gas turbine engine is disclosed. A cooling air valve is operatively disposed at the upstream end of the turbine section to control the admission of cooling air to the turbine in response to engine operating temperatures. In one specific embodiment the thermal growth of the case and the stator elements supported thereby is controlled by the valve. At low power conditions the case and the supported elements grow radially with the rotor in response to increasing gas path temperatures. At elevated conditions cooling air is flowable to the case to retard the thermal growth of the case and allow the rotor to grow radially toward the stator elements.

Abstract: Apparatus forming a portion of the outer wall of the flow path for working medium gases in the turbine section of a gas turbine engine is disclosed. The vanes of each turbine stage are grouped into a plurality of vane clusters which are circumferentially disposed in adjacent relationship about the flow path. A shroud which surrounds the tips of the rotor blades immediately upstream of the vane clusters is segmented in integral ratio to the number of vane clusters. The gap between each pair of adjacent vane clusters is circumferentially positioned in axial alignment with one of the gaps between adjacent shroud segments.