Investigation On The Turbine Blade Tip Clearance Measurement Active Clearance Control And Dumping Identification

Blade tip clearance has been and continue to be a fundamental concern in turbomachinery,which are closely bound up with the efficiency,reliability and structural integrity.The efficiency and reliability of turbomachinery will be improved by BTC measurement and ACC based on blade tip timing(BTT)method.The BTC value does have a significant effect on aerodynamic damping and rotating stall inception.It can not warning early,which is one of the key points for restricting safety operation for turbomachinery,because of the lack of BTC measurement and ACC module,as well as the inaccurate identification of blade damping.Several types of sensors such as eddy-current,capacitance,optical and microwave probes are used to realize this objective.Compared with other probes,eddy current sensor(ECS)is an ideal choice with its advantage of durablity and that it is unaffected by gas stream properties such as contamination,water vapor,and moisture.The purpose of this paper is three fold including BTC measurement,ACC and blade damping identification based on the ECS.(1)In this paper,a eddy current pulse-trigger method(ECPTM)was presented.This method optimizes the static radial and circumferential calibration technology to obtain the sensitivity of the ECS in the different relative locations against the tip of blade.The information from the clearance sensor will be fused with that from the once per revolution(OPR)or key phase sensor.The method is more generally applicable in the condition where the ECS is insufficient sampling caused by the limit of narrow bandwidth,especially under the high blade tip velocity condition.A small scale BTC measurement rig is established to validate the feasibility of this method,which is easy to calibrate with high accuracy based on the designed satic calibration system.Experimental research is carried out on testing rig at different rotating speed.The results show that the method presented in this paper can improve the accuracy of tip clearance monitored by ECS very well.Finally,the precision verification,stability verification and finite element method verification are emploied to prove the efficiency of ECPTM.(2)The second portion of this paper addresses the BTC measurement in different rotating speeds based on the larger scale rig,where a high-bandwidth(100 kHz)eddy current sensor is employed.In this apparatus,the axial displacement and radial displacement of rotor vibration as well as the clearance can be monitored together so that further investigation can be conducted.And the implementation of ACC by axial displacement of the blisk is novel and this paper is the first to present the technique.Besides,an electro-hydraulic proportional position control system(EHPPCS)is employed as the actuator.EHPPCS has the advantages of small size,fast response,resistance to load stiffness,large output and simple operation,which is widely applicable to the automatic control system of industrial power.This system optimizes the geometry shapes of casing and the blade tips to create a linear relationship of BTC values related to the axial displacement of the rotor.And then a voltage/current-BTC values characteristic can be obtained based on proportion integration control method by employing EHPPCS in different rotating speeds.The results show that the BTC value decreases monotonically with the rotating speed increasing and the relative errors are not much bigger than 20%.Finally,the precision verification and error analysis are made.(3)Based on the vibration differential equation of n-degree-of-freedom viscously damped system,the blade damping identification using generalized proportional real modal damping is deduced.And error propagation in this damping identification method is analyzed.The first ten orders mode modal shape of testing blisk are obtained by taking these steps,whih including geometry,channel setup,impact scope,impact setup,measure,validate and modal analysis.And then the frequency-damping ratio characteristic curve of testing blisk was obtained by Gaussian fitting,with a perfect fitting effect.Furthermore,the research addresses advantages and disadvantages of several kinds of rotating blade excitation method,such as inlet turbulent flow excitation,piezoelectric actuator excitation,electromagnet actuator excitation and acoustic excitation method.Finally,a blade damping identification scheme is made based on the larger scale BTC measurement and ACC rig.However,this work is a proof-of-concept demonstration using a laboratory setup providing the basis for BTC active control and blade health monitoring(BHM)based on ECS.