Blade Tip Deflection Research Articles

Integrated fiber optic light probe: Measurement of static deflections in rotating turbomachinery

This paper describes the design, fabrication, and testing of an integrated fiber optic light probe system for monitoring blade tip deflections, vibrational modes, and changes in blade tip clearances in the compressor stage of rotating turbomachinery. The system comprises a set of integrated fiber optic light probes which are positioned to detect the passing blade tip at the leading and the trailing edges. In this configuration measurements of both blade vibrations and steady-state blade deflection can be obtained from the timing information provided by each light probe, which comprises an integrated fiber optic transmitting channel and a number of high numerical aperture receiving fibers, all mounted in the same cylindrical housing. A spatial resolution of 50 μm is possible with the integrated fiber optic technology, while keeping the outer diameter below 2.5 mm. Additionally, one fiber sensor provides a capability of monitoring changes in the blade tip clearance of the order of 10 μm. Measurements from a single stage compressor facility and an engine-fan rig in a 9 ft×15 ft subsonic wind tunnel are presented.

Noninterference Technique for Measurement of Turbine Engine Compressor Blade Stress

A noninterferenc e technique for measuring stress in compressor blades of turbine engines is being developed to alleviate disadvantages associated with conventional strain-gage measurement systems. The noninterference technique uses blade-tip deflection measurements and special data-processing algorithms to infer local blade stress. A prototype of the noninterference technique equipped with a nonintegral blade vibration dataprocessing algorithm has been experimentally validated. The validation consisted of comparing the test results of the prototype noninterference system with those of a conventional strain-gage blade stress data system during an aeromechanical test of a turbine engine. Direct comparisons were made of amplitude and spectral results and real-time monitoring capabilities between the prototype noninterference and strain-gage systems for compressor instability and stall conditions. Expansion of the prototype noninterference processing algorithms to include the capability for inferring blade stress from blade vibrations integral to engine speed is planned for the near future. Longer term efforts will identify the necessary criteria for a multistage compressor noninterference stress measurement system for routine support of aeromechanica l testing.