The need to seal between co-rotating rotor disks in the turbine or other sections of a gas turbine engine is a continuing problem. The environment which such seals must withstand includes exposure of at least one portion of the interdisk seal to the turbine working fluid having temperatures up to 2500F, withstanding the induced centrifugal force caused by high speed disk rotation, and accommodating thermal transient conditions caused by engine throttle changes. It is common for such seals to carry a portion of the rotating seal structure which is located between a stator vane assembly located axially intermediate the turbine disks. This rotating seal is typically comprised of an annular abradable member secured to the radially innermost portion of the stator vanes, and a series of knife edges extending circumferentially about the interdisk seal and extending radially outward into close contact with the abradable annular member. As will be well known to those skilled in the art, radial movement of the interdisk seal can cause the circumferential knife edges to move into contact with the abradable ring, opening a leakage path between the ring and knife edges during normal operating conditions.
One technique in the prior art to provide such interdisk seals has been the use of full ring seal members wherein a monolithic seal structure is established having a radially inner ring spanning the axial gap between the rotor disks, an annular outer wall member sealingly secured at axially opposite ends to the adjacent rotor disk rims, and a radially extending web member secured between the supporting ring and the outer wall for supporting the axially central portion of the outer wall. A drawback with this prior art seal member has been the occurrence of a thermal expansion mismatch between the rotor disks and the seal supporting ring.
During periods of rapid engine acceleration, the working fluid temperature increases rapidly causing the disk rims and seal assembly to also increase in temperature. The interdisk seal, being of significantly lower mass than the disk members, increases in temperature more rapidly and hence experiences more rapid thermal expansion. The differential thermal expansion induced by the uneven temperature rise can cause excessive hoop stresses in portions of the full annular interdisk seal member which may be as great or greater than the hoop stress resulting from the rotation induced centrifugal force. Such monolithic interdisk seals must be fabricated of high strength materials in order to withstand the hoop stresses induced by rotation and the thermal growth mismatch discussed hereinabove. Such strength requires a heavier seal structure further penalizing the overall engine by imposing additional weight adjacent the rotor disk rims.
What is needed is a lightweight interdisk seal which is able to accommodate differential thermal growth between the seal member and the adjacent turbine disks, which can withstand the rotation induced forces, and which is dimensionally stable in the radial direction to avoid excessive radial movement of the rotating knife edges.