Developing a quieter wind turbine – Understanding the effects of blade

generated turbulence and noise

Associate Professor Con Doolan

School of Mechanical Engineering

University of Adelaide, SA 5005

1

The Flow and Noise Group: What we do

• Fundamental and applied research in the area of flow-induced noise (aeroacoustics/hydroacoustics)

• Application areas: Jet noise/airframe noise/helicopter noise/wind turbines/submarine noise/automotive wind noise/fan noise…

• 3 Postdocs

• ~11 HDRs

Facilities

• Anechoic Wind Tunnel

• Anechoic Chamber

• Reverb Chamber

• Large Wind Tunnel

• Excellent Acoustic Instrumentation, including arrays and high-channel-count DAQ systems

• World-class flow instrumentation, hot-wire, laser diagnostics, surface pressure, etc

• Supercomputer facilities

Anechoic Wind Tunnel

Slide 4

Fan

Anechoic Chamber

Collector

Diffuser

Contraction

Silencer

Settling Chamber

Outlet: 275 mm x 75 mm Velocity Range: 3-38 m/s T.I. = 0.3%

Dual Beamforming Arrays

Acoustic “image” for wall-mounted hydrofoil

Adelaide Wind Tunnel

•Cross-section area: 2.75 x 2 square metres •Maximum air speed: 50 m/s (180 km/h) •Turbulence intensity: less than 0.8%

Wind Turbine Wind Tunnel Measurements: about to start

Projects

Airfoil/Hydrofoil Noise Turbulent/Laminar edge noise

Hydrofoil

Recessed Hydrophone

Flow

Wall Mounted Air/Hydrofoils

Cavity/Feedback Loop

RANS-Based CAA

Flow

CFD

Wind Turbines

CAA/DNS

Jet Noise

Wind Turbine Noise: Why is it important?

• Noise emissions are regulated

• Lower turbine noise emissions can ease planning and possibly allow greater numbers of turbines

• Community engagement: sometimes the issue of noise becomes emotive and can affect planning approval

• Quality scientific advice required based on evidence

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This talk…

• How is wind turbine noise generated?

• Blade Swish

• Multiple Turbines

• Atmospheric effects

• Trailing edge noise control

• Future Challenges

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Wind Turbine Unsteady Aerodynamics and Noise

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Convected atmospheric turbulence

Incoming turbulent atmospheric boundary

layer

Wind turbine blade

Gearbox

Blade passes tower as it rotates

Tower

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Blade motion

Tip vortex

Boundary layer turbulence

passing over trailing edge

Atmospheric

turbulence ahead

of moving blade

Blade boundary

layerTrailing edge

Blade Tip

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Spectral Content and Sources

Flow

Turbulence interaction with leading edge: Noise

Turbulence interaction with trailing edge: Noise

Airfoil Noise

Airfoil noise is… • Hard to predict

– Turbulent structure, statistics, anisotropic, non-homogeneous, adverse pressure gradient – too much reliance on empirical models

– Laminar/Transitional Tonal noise: controversial area – feedback loop or global instability with facility effects?

• Hard to measure

– Broadband signal, sometimes hard to distinguish from other sources

– Requires sophisticated techniques: multi-microphone, beamforming arrays – time reversal?

• Hard to control

– Passive noise control methods are difficult to implement and don’t agree with theoretical predictions.

Swish? Trailing Edge Noise Directivity + Convective Amplification

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Phased Array Measurements*

*Oerlemans, S., Sijtsma, P. & Mendez Lopez, B., 2007. Location and quantification of noise sources on a wind turbine. Journal of Sound and Vibration, 299(4-5), pp.869–883. 17

Propagation & Weather Effects

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Atmospheric Boundary Layer

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Day

Night

van den Berg, G., 2004. Effects of the wind profile at night on wind turbine sound. Journal of Sound and Vibration.

Terrain Effects

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Son, E. et al., 2010. Integrated numerical method for the prediction of wind turbine noise and the long range propagation. Current Applied Physics, 10(S), pp.S316–S319.

Reinforcement Model

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Owls: Slient Flight – Silent Turbines?

Sarradj et al. (2010) 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, June.

Tyto Alba – Barn Owl

Oerlemans et al. Reduction of Wind Turbine Noise Using Optimized Airfoils and Trailing-Edge Serrations. AIAA JOURNAL (2009) vol. 47 (6) pp. 1470-1481

Noise Control: Trailing Edge Serrations

Noise Control: Numerical Optimisation of Blades

Marsden et al. Trailing-edge noise reduction using derivative-free optimization and large-eddy simulation. Journal of Fluid Mechanics (2007) vol. 572 pp. 13

Noise Control: Trailing Edge Modifications

HERR and DOBRZYNSKI. Experimental investigations in low-noise trailing-edge design. AIAA Journal (2005)

Brushes

Porous Trailing Edge

Geyer et al. Measurement of the noise generation at the trailing edge of porous airfoils. Experiments in Fluids (2010) vol. 48 (2) pp. 291-308

Passive Control: Serrations

Mean Chord = 165 mm Re = 160,000 – 420,000

Narrow serrations with λ = 3 mm. Wide serrations with λ = 9 mm.

Experiment

Theory

Active Control?

• Amplitude modulation MAY be caused by time-varying reinforcement of nearly synchronised blade motion • Can this be overcome by phase de-synchronisation? • What mechanism dominates – Trailing edge noise? • How many turbines in a row contribute? • Can an active control system be devised?

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Slide 30

UpWind: Design limits and solutions for very large wind turbines, EU 6th Energy Framework, March 2011

Blade Reynolds number Increases with Capacity

Re 9-25 Million

Future Challenges

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Highest Reynolds No. Data we have…

10−1

100

95

100

105

110

115

120

125

130

135

140

St

SP

L1

/3 S

cale

d (

dB

)

NASA 81, Re = 2.88e6

IAG, Re = 2.8e6

VT, Re = 3.05e6

More fundamental experiments are needed to properly understand blade noise, at higher Reynolds number, with better techniques.

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0 2 4 6 8 100

1000

2000

3000

4000

5000

6000

Re/106

f pea

k (

Hz)

Peak radiating frequency vs Size

SIZE

Error ≈ 30%

Thanks

• Australian Research Council, ASC, DSTO, US Air Force, the Sir Ross and Sir Keith Smith Fund

• All my postgrads and postdocs for making me look good

Questions?