Design, Fabrication and Testing of a High-Sensitive Fibre Sensor for Tip Clearance Measurements

A highly sensitive fibre bundle-based reflective optical sensor has been designed and fabricated for Tip Clearance measurements in a turbine rig. The sensor offers high spatial and temporal resolution. The sensor probe consists of a single-mode transmitting fibre and two concentric rings of receiving multimode fibres that collect reflected light in a differential detection gain configuration, yielding a highly linear calibration curve for distance measurements. The clearance measurement range is approximately 2 mm around the central point fixed at 3.2 mm from the probe tip, and the sensitivity of the probe is 61.73 mm(-1). The fibre bundle has been designed to ensure that the distance security specifications required for the experimental program of the turbine are met. The optical sensor has operated under demanding conditions set by the blade and casing design. The experimental results obtained so far are promising and lead us to think that the optical sensor has great potential for online clearance measurements with high precision.This work was funded in part by the Fondo Europeo de Desarrollo Regional (FEDER), in part by the Ministerio de Economia y Competitividad under project TEC2015-638263-C03-1-R, and in part by the Gobierno Vasco/Eusko Jaurlaritza IT933-16 and ELKARTEK (KK-2016/0030, KK-2017/00033, KK-2017/00089 and KK-2016/0059). The work of Josu Amorebieta is supported in part by a PhD fellowship from the Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (UPV/EHU), Vicerrectorado de Euskera y Formacion Continua