New microwave sensing system for blade tip clearance measurement in gas turbines

Real-time clearance control in turbine engines allows improving their efficiency and safety, by enabling prognostics and optimized condition-based maintenance in the turbine hot section. This paper presents a novel 24 GHz microwave sensing system for real-time blade tip clearance monitoring suitable for small-size turbines (aero-engines and aero-derivatives). The system principle of operation is similar to the short range radar technique and employs high temperature resistant circular waveguide resonator probes mounted into the shell of the turbine. Probes concept was proven through simulation and prototypes where built and tested, showing agreement of results. The system was validated in laboratory, where the harsh turbine environment was reproduced on dedicated test rigs. Finally, the system was tested on a real engine, showing its suitability for real-time blade tip measurement.