Introduction ind Turbine Noise and Vibration Dr. Colin Kestell colin.kestell@adelaide.edu.au Colin Kestell Senior ecturer School of Mechanical Engineering The University of Adelaide Engineering Manager until 1997 PhD (Active control of sound in a small single engine aircraft cabin with virtual error sensors) in 000 Teach Engineering Design Noise, here does it come from? An audible vibration transorted to the observer through an elastic solid or fluid. 3 Sound Our ercetion of sound 4 vibrating body malleus (hammer) 50dB A weighting cochlea disturbed viscous fluid tymanic membrane (eardrum) incus (anvil) staes (stirru) 0Hz 1KHz KHz Sound db= 10log = 0log ref ref ref = 0 x10-6 Pascals Imortant to state distance from source 350m away µpascals 100,000,000 10,000,000 1,000,000 100,000 10,000 1000 100 0 150dB 140dB 130dB 10dB Pain 110dB 100dB 90dB 80dB 70dB db 50dB 40dB 30dB 0dB 10dB 0dB Hearing threshold 5 For a oint source radiating into a free field, where the object is small relative to the distance w = = = = 0og( r ) 8dB + 0og( r ) + 8dB 1 1 r 0og( ) r 6dB 1 if r = r r 1 = 10og( = 10og( source ref meas. ref 1 ref = 1x10 atts ref = 0µPascals Fundamentals of Noise and Vibration. M.P.Norton ) 6 ) 9/05/008 1
ind Turbine Noise and Vibration 7 8 For a line source radiating into a free field, where the object is small relative to the distance r = 10og(r ) 5dB = 10og( source ) ref w = + 10og (r ) + 5dB = 10og( r = 1 10og ( ) r1 = 1 3dB meas. ) ref 50 ref = 1x10 1atts if r = r1 db ref = 0µPascals Fundamentals of Noise and Vibration. M.P.Norton 9 Tyes of noise Time domain (s) 10 Time averaged Frequency domain (Hz) Tonal Noise 440Hz 1000Hz 10000 Hz Time (s) Random Noise 53 T = 10og(10 1 10 + 10 10 db +...) 11 Instrumentation - sound A windsock A Microhone A Sound evel Meter hite Noise Pink Noise Conditioning amlifier Vibration 1 Structure-borne vibration transmits energy throughout the entire system. The dislacement of a surface is the combined contribution of all of its modes. hich mode is excited the most is deendent on the source. Each and every exterior surface will radiate sound energy The effectiveness of this radiation is known as the radiation efficiency Sectrum Analyser 9/05/008
13 14 Measuring Vibration Vibration Measured in terms of Dislacement Velocity Acceleration sometimes in terms of g (gravity) Measuring sound and vibration Instrumentation - vibration Conditioning amlifier db also used or absolute units on either a logarithmic or linear scale Be careful of units! aser vibrometer All this and more covered in Part IIA 3C6 Vibration and Part IIB 4C6 Advanced inear Vibration Accelerometer Strain gauge Sectrum Analyser Measuring sound and vibration Calibration 15 ind Turbine Noise 16 hat generates the noise in wind turbines? 17 ind Turbine Noise 1. Blades 18. Rotor 3. Pitch 4. Brake 5. ow seed shaft 6. Gear box 7. Generator 8. Controller 9. Anemometer 10. ind Vane 11. Nacelle 1. High seed shaft 13. Yaw drive 14. Yaw Motor 15. Tower 9/05/008 3
Note, much larger gearbox and hence many more moving arts 19 Aerodynamic Noise Blade asses through turbulent, often gusty flow Blade motion causes turbulence ing ti vortices cause turbulence Turbulence creates sound (broadband audible ressure erturbations) Turbulence higher as each blade asses tower Consider a 3 blade, 6 rotor will have a BPF of 1.3 Hz 0 Aerodynamic Noise 1 A 3 blade, 6 rotor will have a tower BPF of 1.3 Hz, or a eriodic time of 0.77 seconds 0.77s Shaft noise unbalanced bent shafts non-concentric alignment 3 Shaft noise 4 frequency ( Hz) = frequency ( Hz) = 9/05/008 4
Shaft noise 5 Shaft noise 6 Amlitude Varies with shaft seed frequency ( Hz) = Vary with seed 7 8 Shaft frequency( Hz) = Amlitude Mesh frequency( Hz) = N. Gear with N teeth Consider gear airs with a simle ratio: :1, 3:1 etc Periodically the same teeth will mesh At a frequency equal to the shaft frequency of the larger gear One full revolution of the large gear, also returns the small gear to the same lace Gears that share common multiles also mesh the same two teeth eriodically. Consider: a 40 tooth inion and a tooth srocket, Turn the srocket TO FU turns, moving 10 teeth ast a oint. This moves 10 teeth on the inion, driving it THREE FU turns. 9 This cyclic nature is known as the HUNTING TOOTH. The frequency is equal to: Gear mesh frequency owest Common Tooth Multile This causes uneven wear Choose tooth numbers that result in a high lowest common multile to kee this frequency as low as ossible This is why gears have aarently strange teeth numbers 30 9/05/008 5
31 3 Probable 14 tooth gear issue Drive seed F F 1 htt://www.vibanalysis.co.uk/ Gear Box Failure 33 Normal sur gears cost effective 34 Helical gears smoother mesh, more exensive, roduce an axial force comonent as well as a tangential Herring bone gears (far more exensive) realign the resultant force Bearing Noise htt://www.vibanalysis.co.uk/ 35 Generator Noise 36 A tyical 3-hase generator will have 3 airs of (6) oosing wound coils 4 rotating ermanent magnets Producing 1 ulses er revolution 9/05/008 6
Vibration isolation m Acoustic resonance 38 ω = k m c k Increase mass or decreased stiffness The large tower will act like an organ ie Broadband and tonal noise will roagate through the duct and excite standing wave resonances Increased daming Dislacement Radiation 39 Examles Vesta V5-850 k, 3 Blade, 6 40 Psycho-acoustic characters of relevance for annoyance of wind turbine noise. K. Persson aye and E. Og Hrstrog M. journal of sound and vibration (00) 50(1), 65-73 Examles indorld 0k, Enecon 500k 41 Examles Canadian 1.5 M ind Turbine Sectogram 4 5000 0 0 40 dbafrom 70m Psycho-acoustic characters of relevance for annoyance of wind turbine noise. K. Persson aye and E. Og Hrstrog M. journal of sound and vibration (00) 50(1), 65-73 ind turbines and sound: Review and best ractice guidelines. HGC Engineering 5 0 5 10 Time (s) 9/05/008 7
Examles Acoustic model of tyical wind turbine sound roagation ind turbines and sound: Review and best ractice guidelines. HGC Engineering 43 Noisy or quiet? db= 10log = 0log ref ref ref = 0 x10-6 Pascals Imortant to state distance from source 350m away µpascals 100,000,000 10,000,000 1,000,000 100,000 10,000 1000 100 0 150dB 140dB 130dB 10dB Pain 110dB 100dB 90dB 80dB 70dB db 50dB 40dB 30dB 0dB 10dB 0dB Hearing threshold 44 Machinery health monitoring Noisy or quiet? 46 In-situ microhones, strain gauges and accelerometers on Rotating machinery Critical structures Baseline measurement Subsequent measurement Many claim that the noise is worse at night or in the early hours of the morning. ess masking (other noises covering it u) Physiological issues Meterological effects Noisy or quiet? 47 Noisy or quiet? 48 Normal conditions One of a few meteorological effects armer air thermal inversion layer 9/05/008 8