Turbo machine tip clearance and vibration measurements using a fibre optic laser Doppler position sensor

Abstract

This paper presents a novel fibre optic laser Doppler position sensor for single blade tip clearance and vibration measurements at turbo machines, which offers high temporal resolution and high position resolution simultaneously. The sensor principle is based on the generation of a measurement volume consisting of two superposed fan-like interference fringe systems with contrary fringe spacing gradients using wavelength division multiplexing. A flexible and robust measurement system with an all-passive fibre coupled measurement head has been realized employing diffractive and refractive optics. Measurements of tip clearance and rotor vibrations at a transonic centrifugal compressor performed during operation at up to 50 000 rpm (833 Hz) corresponding to 21.7 kHz blade frequency and 586 m s−1 blade tip velocity are presented. The results are in excellent agreement with those of capacitive probes. The mean uncertainty of the position measurement was around 20 µm and, thus, considerably better than for conventional tip clearance probes. Consequently, this sensor is capable of fulfilling the requirements for future active clearance control systems and has great potential for in situ and online tip clearance and vibration measurements at metallic and non-metallic turbine blades with high precision.

Model assessment of a composite mock-up bladed rotor based on its vibration response and radial expansion

“…The sensor measures the surface distance with micron uncertainty and was already applied for metallic rotors at velocities of around 600 m/s [16]. Concerning metallic rotors, its capability of measuring the radial expansion with a measurement rate of several 10 kHz was already demonstrated [17].…”

“…The measurement principle of the LDD sensor is based on a MachZehnder interferometer, which employs an interference fringe system and enables the measurement of the velocity v of a rough surface [19]. In order to enable a simultaneous measurement of the axial position z the LDD sensors employ two superposed interference fringe systems [16]. The two scattered light signals s i ðtÞ, with i ¼ 1; 2, are distinguished by wavelength division-multiplexing.…”

Current Status and Prospects of High-Power Fiber Laser Technology (Invited Paper)

“…레이저의 출력 수준이 상승하고, 빔 품질이 향상됨에 따라 레이저는 통신, 정밀 측 정, 바이오, 의료에서부터 대형 구조물의 드릴링, 용접, 절단, 또한, 국방에 이르기까지 폭넓은 분야에서 중추적인 기술 요 소로 자리 매김을 하고 있다 [1][2][3][4][5][6][7][8] . 레이저 시스템은 다양한 방 식으로 구성될 수 있는데, 최근에는 광섬유를 이득 매질로 하는 광섬유 레이저가 벌크(Bulk) 방식 레이저 시스템과 대 비되는 다양한 장점에 힘입어 많은 연구 및 개발 관심을 받 고 있다 [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] .…”

On the development of a magnetoresistive sensor for blade tip timing and blade tip clearance measurement systems

“…For instance, they have been used for comparisons with other sensor type (Cardwell et al [2]), to validate a new tip-timing technique (Gallego [3] and Heath [4]), to realize a laser doppler system (Pfister [5]) or to compare the results with the consolidate strain gauge technique (Rossi et al [6 -8]). However, optical probes suffer of low tolerance to debris and shading problems [9].…”