CAPACITIVE MEASUREMENT OF COMPRESSOR AND TURBINE BLADE TIP TO CASING RUNNING CLEARANCE

It is an established fact that the efficiency of a gas turbine engine has an inverse relationship with the clearance between the rotor blade s and the casing (Tip Clearance, or TC). TC is an essential measuremen t during the testing of development engines. While commercial TC measu rement systems are available, their applicability to an engine is dict ated by engine size, geometry, physical accessibility, and temperature distribution around the measurement region. This paper describes the development of a TC measurement system, based on the capacitive measur ement principle, which was undertaken to satisfy the application requi rements of a specific class of gas turbine engines. The requirements i ncluded a relatively long and flexible cable to route the electrical s ignals out of the engine. The TC measurement system was successfully u sed during engine testing and valuable data were obtained.