Patent ID: 7140836
Filing Date: 2006-11-28
Classification: F01D

Abstract:
1. A casing arrangement for surrounding a rotary component of a gas turbine engine comprises an annular supporting structure, a circumferentially extending array of part annular members suspended from the supporting structure, a fluid chamber arranged to receive a supply of heat transfer fluid from a source thereof at a pressure dependent upon engine speed, fluid conduit means in open communication with the fluid chamber at one end and a region of lower pressure at the other end, and in thermal contact with the supporting structure whereby to influence the extent of thermal expansion and contraction of the supporting structure in accordance with a pressure differential between the fluid chamber and the region of lower pressure, and at least one fluid pressure bleed hole leading from the chamber, the size of the at least one pressure bleed hole relative to the total inlet area of the fluid conduit means being chosen such that, when fluid chamber pressure increases during engine acceleration, above a predetermined pressure the bleed flow from the chamber is choked so that further increases in pressure act across the fluid conduit means, and when fluid chamber pressure decreases during engine deceleration and the bleed flow is no longer choked a greater proportion of total flow passes through the at least one fluid pressure bleed hole.