An Optical Fiber Blade Tip Timing Sensor Capable Of Resisting Tip Clearance Fluctuation

It is easy to be damaged and fractured for the rotor blades which is a key component of an aeroengine in bad operation environment,such as high temperature,high pressure,high speed and high load,by which the safety on aeroengine is affected.Therefore,it is necessary to monitor the health status of blades online in real time.The health status of rotating blade affects the vibration and stress distribution,so the operation status of rotating blade can be monitored by measuring the vibration and stress distribution.Due to these advantages of optical fiber,including response quikly,high precision and anti-electromagnetic interference,optical fiber blade tip timing sensor is widely used to monitor the health status of rotating blades.However,the tip clearance between optical fiber tip timing sensor and blade tip will be changed by many factors such as thermal expansion caused by temperature change,assembly error and blade vibration,then the tip timing signal will be changed,the times of arrival will bu changed,which results in the blade tip timing error.Therefore,a new type of optical fiber blade blade tip timing sensor based on the double circular coaxial optical fiber blade tip timing sensor is designed in this thesis.Structure paramaters is adjusted to makes the light intensity modulation function of the new optical fiber blade tip timing sensor be constant in a specific range of tip clearance,so as to prevent blade tip timing signal being influenced by blade tip clearance fluctuations.Therefore,the error of times of arrival can be reduced.This thesis firstly presents research background and significance of rotating blade detection technology,introduces difference blade tip timing sensors which differ in structure and principle,including the optical fiber blade tip timing sensor.And principles and disadvantages of methods of reducing blade tip timing error introduced by fluctuated tip clearance is presentated.Moreover,main works of this thesis is introduced.Secondly,the structure of the sensor probe is introduced.And by means of simulation,while blade tip clearance fluctuats,the influencing mechanism about tip timing error influenced by structure paramaters of the new optical fiber blade tip timing sensor is studied.Optimal structure paramaters of optical fiber blade tip timing sensor are determined.Thirdly,the principle and structure of the new optical fiber blade tip timing sensor is presented.The tip timing error in varing tip clearance is studied by means of a mathematical model.It is conclued that the light intensity modulation function is constant in a specific tip clearance range of 1～1.5 mm.Compared with the traditional coaxial sensor,the new optical fiber blade tip timing sensor can reduce relative error of displacements of arrival by 100 %.Therefore,the feasibility of the new type of optical fiber blade tip timing sensor is proved.Finally,a blade tip timing measurement system is builted.After calibration,the new optical fiber blade tip timing sensor is tested,the tip timing error in varing tip clearance is measuremented.It is concluded that the light intensity modulation function is constant in a specific tip clearance range of 1.25～2 mm.Compared with tip timing error of the traditional coaxial optical fiber blade tip timing sensor,standard deviation of times of arrival of the new optical fiber blade tip timing sensor is reduced by 48.83%.The superiority of the new blade tip timing sensor is verified,which can reduce tip timing error in varing tip clearance.