Electromechanical Measurement of Turbomachinery Blade Tip-to-Casing Running Clearance

Abstract

It is difficult to make a reliable measurement of running clearance in the hostile environment over the blading of modern gas turbines. When the engine manufacturers require the measurement to be made during tests lasting many hours, or even days, measurement system ruggedness and reliability are of primary importance. This paper describes how a second generation tip clearance measurement system of much reduced size and weight was developed. The reduction of size and weight facilitates the use of this measurement system for blade tip-to-casing measurements on all engine development tests from rig to flight worthy engines. During the course of commissioning, the measurement system was tested first in the laboratory, then on progressively more demanding test vehicles. The final test was on the high pressure turbine of a modern military full scale development single spool core. During the course of this test, the mean engine Turbine Entry Temperature through the blading over which clearance was measured, exceeded 1800 K and is typical of the applications for this second generation system.