A technique for the measurement of blade tip clearance in a gas turbine

This paper describes a capacitance-based tip clearance measurement system which engineers have used in the most demanding turbine test applications. The capacitance probe has survived extended use in a major European gas turbine manufacturer's high-temperature demonstrator unit, where it functioned reliably at a turbine entry temperature in excess of 1800 degrees Kelvin. This paper explores blade by blade tip clearance measurement techniques and examines probe performance under laboratory conditions in support of high-temperature installations. The paper outlines the blade by blade tip clearance measurement technique and describes the experimental facility used to study tip clearance measurement. The paper also fully describes the method used to calibrate the measurement system in order to ascertain measurement accuracy. The paper clarifies how the practical problems were overcome associated with making blade by blade tip clearance measurements in both compressor and turbine environments. Since its initial development, gas turbine development programmes have routinely used the clearance measurement system. The inherent robustness of the system has resulted in reliable in-service measurement of clearance in real world applications.

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Blade by Blade Tip Clearance Measurement

: Turbine tip clearance design and prediction techniques have been limited to analytical methods for lack of an accurate direct measurement device. It was the purpose of this program to substantiate prediction correlations utilizing direct measurements from a laser-powered miniaturized turbine tip clearance device (MTCMD) previously developed under Applied Technology Laboratory support. The resultant comparisons of measured versus analytically determined clearances based on measured temperatures would be used to verify or to improve the analytical techniques.

Lawrence C Baker

Papers

Turbine Tip Clearance Measurement.