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HEATED TRAILING EDGE PATCH FOR REDUCTION OF FLOW-INDUCED NOISE IN A COMPRESSIBLE FLUID

IP.com Disclosure Number: IPCOM000245996D
Publication Date: 2016-Apr-25
Document File: 6 page(s) / 190K

Publishing Venue

The IP.com Prior Art Database

Abstract

A technique for reducing flow-induced noise in a compressible fluid of a wind turbine airfoil is disclosed. The technique includes transferring heat from a surface of the airfoil into the compressible fluid on a short patch upstream of a trailing edge of the airfoil. The heat transfer can change shape of a mean boundary layer profile and its fluctuation parameter distribution beneficially, such that noise emission is reduced. Further, heat transfer into the compressible fluid via a heated surface patch allows the compressible fluid to expand, thereby, reducing density of the compressible fluid in a lower part of the BL. The expansion also results in a small local acceleration, which affects convective velocity with which the turbulent structures are moving over the TE. Furthermore, the heating patches may be spanwise segmented to avoid loss of a complete patch in case of damage, to adapt to the locally different flow velocity causing inhomogeneous heating and to enable a spanwise detection of separated regions.

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HEATED TRAILING EDGE PATCH FOR REDUCTION OF FLOW-INDUCED NOISE IN A COMPRESSIBLE FLUID

BACKGROUND

 

The present disclosure relates generally to wind turbines and more particularly to a technique for reducing flow-induced noise in a compressible fluid of a wind turbine airfoil.

Generally, wings and rotor blades, for example, those on wind turbines, suffer from turbulent boundary layer (TBL) noise emitted at a trailing edge (TE) of the blade. TBL noise can place expensive constraints on operating parameters of the wind turbine while working within limits of noise emission. TBL noise is generally generated by two mechanisms. One mechanism is scattering of pressure fluctuations the TBL eddies impose on the wall, creating a typically non-compact dipole source. Another mechanism is the quadrupole sources in the TBL itself.

Regulations pertaining to wind parks require working within prescribed noise limits. When application of strong Noise Reduced Operating (NRO) modes is required, working within noise limits can cause severe loss of Annual Energy Production (AEP) of the wind park.  Reduction in wind turbine source noise level can improve the net present value of a wind park or allow reduction of liquidated damages payments.

It would be desirable to have a technique to reduce source noise level in a wind turbine.

 

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 depicts a patch on a blade or a wing to introduce heat into a boundary layer.

Figure 2 depicts an arrangement of a thermal insulator and a heating element on an airfoil.

Figure 3 depicts graphs comparing change of spectrum with a heated patch in the airfoil to that without the heated patch.

Figure 4 depicts a Constant Temperature Anemometer (CTA) circuit for temperature control.

Figure 5 depicts spanwise segmented heating patches over the airfoil.

DETAILED DESCRIPTION

A technique for reducing flow-induced noise in a compressible fluid of a wind turbine airfoil is disclosed. The technique includes transferring heat from a surface of the airfoil into the compressible fluid on a short patch upstream of a trailing edge of the airfoil. The heat transfer can change the shape of a mean boundary layer profile and its fluctuation parameter distribution beneficially, such that noise emission is reduced.

Heat transfer into a boundary layer of the airfoil results in increase of temperature, thereby, reducing density of the compressible fluid close to a wall of the airfoil. This principle is used to alter a boundary layer (BL) profile shape to optimize turbulent boundary layer (TBL) - trailing edge (TE) noise emission by adjusting to a shape parameter that is beneficial for noise. Further, turbulent fluctuations are influenced to have less kinetic energy close to the wall. As scattering of turbulent fluctuations into sound is approximately inversely proportional to the square of distance from the airfoil (~1/r²), radiated noise can be reduced. As a positive side effect, the airfoil can then be optimized to be...