Turbomachinery blade tip measurement technioues

The efficiency of axial flow compressors and turbines is critically dependent on the size of the tip to casing gaps (tip clearance) as is the surge margin of compressors. Optimisation of tip clearance control schemes requires measurements of tip clearances throughout the operating envelope of the engine. The dynamic design of rotor blading to avoid damaging integral order and self excited resonance's is complex and still defies routine right-first time design. This necessitates monitoring of blade vibration during testing which is time consuming and costly with conventional strain-gauging techniques. Both of the above requirements may be addressed by easily mounted tip probes, the design and operation of which are discussed in this paper. Until recently the market for such devices has provided insufficient incentive for instrumentation suppliers to invest in the development of such devices leaving engine manufacturers to develop their own solutions to these unique problems. The Rolls-Royce experience is described.