LASER DOPPLER VIBROMETRY ON ROTATING WIND TURBINE BLADES

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1 Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung IOSB - Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB - LASER DOPPLER VIBROMETRY ON ROTATING WIND TURBINE BLADES P. Lutzmann a, B. Göhler a, C. Scherer-Kloeckling a, N. Scherer-Negenborn a, S. Brunner a, F. van Putten a and C. A. Hill b a Fraunhofer Institute of Optronics, System Technologies and Image Exploration IOSB, Ettlingen, Germany b Malvern Lidar Consultants, Malvern Link, United Kingdom 18 th Coherent Laser Radar Conference June 27-July 1, 2016 Boulder, Colorado Ettlingen Karlsruhe Ilmenau Lemgo Fraunhofer IOSB 1

2 Status of Wind Turbine Engines Very strongly expanding market of WTG (on-shore and off-shore plants) Costs for plants and components rising with powering and sizing Need to monitor and analyse their performance are growing steadily Quality standards gaining weight Construction Installation Operating control Maintenance Growing willingness to invest in innovative sensors Vibration loading (caused by mechanical, wind and aerodynamic effects) One essential failure factor Fraunhofer IOSB 2

3 Present Sensor Techniques for Vibration Diagnostics Accelerometers (i. e. condition monitoring systems / CMS) Microfon arrays ( acoustic camera ) Photogrammetry (stereo cameras) Accelerometer Condition Monitoring System (CMS) Source: µ-sen GmbH Acoustic Camera Source: Photogrammetry Source: Laser Doppler vibrometry useful supplement to the existing sensors? Fraunhofer IOSB 3

4 Laser Doppler Vibrometry Benefits: Contactless and remote sensing Very flexible (number of conventional sensors are limited) No direct installation at the plant Mobile and low setting-up time Various scanning strategies possible Vibration measurement at mast, nacelle as well rotating blades LDV? However, a multi-channel receiver is difficult to realize (mode analysis) Range: ~ 300 m or more! Fraunhofer IOSB 4

5 Application Areas Using Laser Doppler Vibrometry Condition monitoring Fault diagnostic Optimizing of wind power plants with regard to vibration loading Sound emission exspection Avoiding of powering down because of component failures Validation of simulation models Valueable in WTG development phase (i.e. modal analysis test, correlation to CAE models) Fraunhofer IOSB 5

6 Concept of Image Based Tracking System Why new concept? Present status of LDV Scanning of stationary objects Only spinning objects viewed from a point on their spin axis Limited range laser vibrometer tracking camera pan/tilt head Optional: Fixed LDV (phase sychronisation) Fraunhofer IOSB 6

7 Concept of Image Based Tracking Image processing steps of the real-time software Initialisation phase Identifying the three blade tips Tracking phase Generating of a dynamic 3D model of the moving rotor Locating the laser spot by using a hotspot detector ( fine tracking ) SWIR images (under different weather conditions) Fraunhofer IOSB 7

8 Laser Doppler Vibrometer Using Polarisation Diversity Parameters of laser Doppler vibrometer Wavelength 1.56 µm Output power up to 1W (typ. 200 mw) Macro Doppler shift (max.) +/- 60 MHz Laser divergence 100 µrad Laser safety class 1M (200 mw), 4 (1 W) Receiver VIS zoom camera Transmitter Pilot laser (532 nm) In-house-developed laser Doppler vibrometer Fraunhofer IOSB 8

9 SNR Improvement by Using Polarisation Diversity Technique Laser beam Screen Speckle Pattern Measurement result Diffuse object Lens s-pol. and p-pol. pattern uncorrelated p-pol + = s-pol p-pol s-pol Combined polarisation states Frequency is detectable ony after combining! Fraunhofer IOSB 9

10 IF Time sequence of macro Doppler Progress of measurement: green already done red still to measure I&Q data Fraunhofer IOSB 10

11 Field Trial on June 2016 First Measurements of a Wind Turbines Fraunhofer IOSB 11

12 Estimated Line-of-Sight Macro Doppler Shifts Geometrical model Wind turbine scale model Real wind turbine (Vestas V90 2.0) Symbol Parameter h 0 Sensor height 1.4 m 1.4 m d Rotor diameter 2 m 90 m h Spinner height 4.15 m 95 m R a Range (measuring system base point of WTG) Angle between rotor plane normal and horizontal 7.5 m 250 m 500 m 0 5 T Revolution period (typ.) 5.1 s 6.2 s LOS velo LOS velocity (max.) 0.43 m/s 15.3 m/s 8.9 m/s Df macro Macro Doppler shift (max.) +/- 558 khz +/ MHz +/ MHz Fraunhofer IOSB 12

13 Measurements on Rotating Wind Turbine Blades Macro Doppler Shift Wind turbine scale model Hub height = 4,15 m Range to base point = 7,5 m Radius to measurement point = 0,8 m Wind turbine Vestas V90 Hub height = 95 m Range to base point = 335 m Radius to measurement point = 36 m Fraunhofer IOSB 13

14 Measurement on Rotating Outdoor Wind Turbine Model Stationary Shaker External excitation by shaker Sychronized on exciting shaker frequency (phase) Setup FFT (arbitrary point) 2. Mode (cantilever slab) Dynamic External excitation by shaker Sychronized on exciting shaker frequency (phase) Fraunhofer IOSB 14

15 Static Measurements: Mast and Nacelle SWIR 1 SWIR Laser spot 2 3 vibrometric image ( Hz) IF deviation Vibations transferred mainly from the drive shaft onto the nacelle body shell First natural frequency of 0.33 Hz (rotor diameter: 25 m,hub height: 70 m) Fraunhofer Institute of Optronics, System Technologies and Image Exploitation

16 Final remarks We have developed a new system based on a laser Doppler vibrometer - for measuring wind turbine vibrations, especially rotating blades With our constructed system we have demonstrated the functionality of the concept and the required accuracy of the technology Developing of tracking algorithms and hardware configuration Laser Doppler vibrometry could be a supplemental sensor of high potential for inspecting and designing new wind turbines Showing first measurements on rotating wind turbine blades Future work: measurements of different real wind turbine engines, deeper analysis and further system improvements Fraunhofer Institut für Optronik, Systemtechnik und Bildauswertung 16