Shape Memory Alloy Adaptive Control of Gas Turbine Engine Blade Tip Clearance

Blade tip clearance in a gas turbine is critical; each increment of tip clearance reduction increases efficiency and reduces fuel consumption. In this study only the compressor section will be treated. Using a Lycoming T55L-712 turboshaft engine, which has wide commercial and military application, two stages of the compressor section will be modified to accept a shape memory alloy ring whose inner diameter changes with temperature. The compensator ring will be fabricated of an alloy whose transformation temperature is suited to the stage 2 and stage 3 of this turbine, and the design and thermo-mechanical processing of the ring will be such that when the turbine has reached operating temperature, the ring diametral change will reduce the tip clearance to approximately 0.001". Performance will be evaluated for a range of ambient air temperatures encountered, and the stability of the compensator ring as a function of cycles of operation and dwell time at operating temperature. The tip clearance compensation by the shape memory induced diameter change of a ring insert would substantially improve engine efficiency and fuel consumption. Systems for accurately locating the rings in the shroud in both the axial and radial direction will be developed as well as concepts to facilitate assembly. Considerations will be given to extending the concept to the entire compressor section.