HIGH-SPEED ROTOR TIP CLEARANCE MEASUREMENTS IN A TRANSONIC COMPRESSOR

Performance of a gas turbine compressor is directly dependent on the size of the region between the rotor blade’s tips and the surrounding casing, the tip clearance, which dynamically changes with rising rotor speed due to rotor blade radial growth from centrifugal loading. Too large a tip clearance introduces disruptive air flow that will lower compressor efficiency and lead to stall conditions, whereas too small a tip clearance will increase the risk of blade tip rubbing with the casing inner wall and may lead to catastrophic failure. This experiment is a part of a program of research that characterizes the Naval Postgraduate School Military Fan (NPSMF) in the Turbopropulsion Lab’s (TPL) Transonic Compressor Rig (TCR). This study involves the design, creation, and use of two benchtop rigs with a capacitive proximity probe blade tip clearance measurement system to develop mathematical methods to post-process capacitive probe output signals for calibration and tip clearance measurements. The mathematical methods developed in this study are validated against the tip clearance measurement system manufacturer’s method, showing improvement. A comparison of the different calibration rigs’ resulting calibration curves is discussed. The post-process method is then applied to high-speed tip clearance measurements of the NPSMF in the TCR and the results are compared to a model.Office of Naval Research, Arlington, VAOutstanding ThesisLieutenant, United States NavyApproved for public release. Distribution is unlimited