Aerodynamic Structural Noise - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 199

7

Aerodynam ic Structural Noise

7.1 Introduction

Low-noise.wind.turbine.blades.are.being.manufactured.with.hybrid.iber-
glass-reinforced.materials.that.are.capable.of.bearing.directional.loads.and.
are.used.in.the.construction.of.wind.turbine.blade.parts.or.entire.sections..
The. use. of. such. materials. inluences. the. air. low. over. them. in. such. a. way.
that.the.resulting.boundary-layer.turbulence.is.damped.in.a.controlled.way,.
thus.weakening.the.noise-scattering.mechanism.at.the.trailing.edge,.and.the.
scattered.acoustic.waves.are.absorbed.and.attenuated.by.the.material.acting.
as.an.acoustic.liner.

7.2 WindTurbineAerodynamics

The.wind.turbine.aerodynamics.of.a.horizontal.axis.wind.turbine.(HAWT).
are. not. straightforward.. The. air. low. at. the. blades. is. not. the. same. as. the.
airlow.farther.away.from.the.turbine..The.very.nature.of.the.way.in.which.
energy.is.extracted.from.the.air.also.causes.air.to.be.delected.by.the.turbine..
In.addition,.the.aerodynamics.of.a.wind.turbine.at.the.rotor.surface.exhibit.
phenomena. that. are. rarely. seen. in. other. aerodynamic. ields. 1 . Wind. speed.
increase.during.hurricanes.is.shown.in.Figure 7.1.
Wind.turbines.with.vibration.damping.are.acoustically.optimized.to.reduce.
the.resonant.vibrations.and.enhance.the.sound.transmission.loss.of.the.blade.
structures.. Damping-covering. layers. also. provide. maximum. absorption. of.
sound.with.minimum.thickness.and.weight.

7.2.1 Axial Momentum and the Betz Limit

We.can.show.schematically.upwind.and.downwind.rotor.emissions..Energy.
in. luid. is. contained. in. four. different. forms:. gravitational. potential. energy,.
thermodynamic. pressure,. kinetic. energy. from. the. velocity,. and,. inally,.

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