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Blade tip clearance is a key design parameter for gas turbine designers. This parameter is often measured during engine testing and development phases as part of design validation but has yet to be utilized during normal engine fleet operation. Although blade tip clearance measurements are often mentioned for fleet operation in the context of active clearance control, the use of blade tip clearance measurements can provide an additional benefit for engine health monitoring. This paper explores the use of blade tip clearance sensors for engine condition monitoring of hot section blades. Blade tip clearance, especially in the first stage turbine, has an impact on exhaust gas temperature. The use of tip clearance measurements can provide supplementary information to traditional EGT measurements by providing a direct measurement of wear on the blade tips.

Time Domain Reflectometery (TDR) is a Radio Frequency (RF) technology that has been used for many years to find cable breaks and measure fluid levels in industrial processes. The technology uses picosecond length pulses and the associated reflections off the fluid surface in a time of flight measurement to determine fluid height. TDR signals have additional information that can be processed and utilized for Integrated Vehicle Health Management (IVHM) applications. For example, when water collects in the fuel tank, TDR is capable of identifying and measuring the amount of water. This can allow the water sumps to be drained on condition instead of on a schedule. In addition, electromagnetic properties of the fluid can be determined, such as the dielectric constant, which can be used to identify mis-fueling situations, contaminants in the fluid, and potentially other fluid health properties.