Rotating Blade Tip Clearance Measuring Technique Using Blade Tip-timing And Dual-frequency Laser Phase Ranging

Tip clearance refers to the small distance between the rotating blade tip and the enginecasing of large-sized rotating machinery, for example aircraft engines, steam turbines,gas turbines.It is an important parameter for these machinery, since it has a greatinfluence on the machinery’s healthy and safe operation, and the energy conversionefficiency of the engines. Therefore, the real-time and high precision tip clearancemeasurement technique is one of the key technologies to carry out the engine’s healthmonitoring and the active control of tip clearance, and one of the main bottlenecksthat restricts the development of the engines.A tip clearance measuring technique ofrotating blades using blade tip-timing is proposed in this thesis, besides, themeasurement model of the measuring system is established.In accordance with themeasurement model, the design requirements of each part is analyzed and detailedlydesigned.Then the error sources of the measurement system is analyzed in theory, andthe corresponding performance optimization schemes are proposed. Basing on theexisting experimental platform, the preliminary tip clearance measurementexperiments are undertaken to test the performance of measuring system.In addition,the main disadvantages of the tip clearance measuring system using dual frequencylaser with large frequency difference is also analyzed in this thesis. The anti same-frequency crosstalk optimization is designed and the double optical fiber transmissionphase tip clearance measuring experiment is accomplished.The main work includesthe following four sections.Firstly, based on laser triangulation method and optical fiber sensing technology, a tipclearance measuring technique of rotating blades using blade tip-timing is proposed,and the mathematical model of the measuring system is established. Using the risingedge of the blade tip arrival signal as the tip timing signal overcomes the influences inprinciple from the factors,such as the instability of the laser,the change and the drift ofthe reflected light intensity caused by the different blade surface scatteringcharacteristics and the change of the medium inside the rotating equipment, thechanges of the signal amplitude caused by the changes of some circuit parameters.Thus, the measuring system has many advantages, for instance, a fast speed atdynamic response, high stability, good ability of anti-electromagnetic interference andhigh measuring precision.Secondly, the error sources of tip clearance measuring system based on blade tiptiming is analyzed systematically according to the mathematical model. On top on this,the main error factor of the measuring system is infered. Also the the improvementmeasures and the corresponding technical solutions are suggested. Then the potentialaccuracy of the measuring system is discussed in detail. Thirdly, through introducing the blade tip timing sensor and the tip clearancecalculation software, the debugging experiment of the blade tip clearance measuringsystem is completed based on the existing experimental rotating platform and theblade vibration detection system using blade tip timing. In addition, a group of tipclearance measuring experiments from low constant speed to high constant speed ofrotating blade were carried out. The experiment data verifies the correctness, thefeasibility and the advantages of the measuring system preliminarily.Finally,the optimization design of the processing circuit of the tip clearancemeasuring system using dual frequency laser with large frequency difference is doneto improve the ability of anti-electromagnetic interference of the measuring system.