Airfoil Self Research Articles

Numerical simulation of far field acoustics of an airfoil using vortex method and 2-D FW-H equation

Airfoil self noise is the main noise source of large wind turbine blades and aircraft wings. Unsteady flow field of NACA0012 airfoil has been simulated numerically in this paper using vortex method, and validation has also been done. Far field acoustics of circular cylinder at Reynolds number equals 150, 200 and 2000 have been simulated and validated numerically in this paper, as unsteady load of target object being acoustic source. The result of far field acoustics of circular cylinder shows that the maximum sound pressure points are in the line perpendicular to the coming flow, which is consistent with other papers. And comparison with paper about NACA0012 airfoil at Re=200 shows that the directivity is in a good agreement. Work of this paper paves the way to further investigation of acoustics prediction of wind turbine blades.

Airfoil self noise reduction by non-flat plate type trailing edge serrations

This paper represents the results of a preliminary study which aims to reduce the airfoil trailing edge self noise by employing non-flat plate type trailing edge serrations. This configuration offers better structural strength and integrity, as well as a more straightforward manufacturing process compared to the conventional flat plate type serrations. We found that the non-flat plate serration not only reduces the broadband self noise significantly, but also eliminates the high-frequency noise that was observed by others who used flat plate type serration. However, due to the presence of certain bluntness at the sawtooth root, vortex shedding noise in a narrow frequency bandwidth is also produced. This extraneous noise is found to be less significant if a wider-angle serration is used. To increase the effectiveness of the proposed serration geometry a hybrid configuration composed of a non-flat plate type trailing edge serration with woven-wire mesh screen is employed for the reduction of the narrowband vortex shedding noise.

Integrated numerical method for the prediction of wind turbine noise and the long range propagation

Characteristics of noise propagation from wind turbine have been studied by using the integrated numerical methods based on Ray theory. There are two numerical approaches in this paper. Those are constructing noise sources of wind turbine and computing the noise level on the ground. First of all, the flow fields around the wind turbine blade are calculated using Wind Turbine Flow, Aeroacoustics and Structure analysis (WINFAS). WINFAS is an unsteady vortex lattice methods based on potential flow. The results of flow analysis are used for predicting tonal noise, turbulence ingestion noise, and airfoil self noise. Tonal noise is induced by the displacement of fluid and loading fluctuation of the blade and those are predicted by Farassat 1A equation. Moreover, semi-empirical formulas are used for the prediction of broadband noise such as the airfoil self noise and turbulence ingestion noise. Before the beginning of the next step, the acoustic pressure is integrated at the each point of virtual acoustic sphere considering retarded time. It also represents the noise directivity on wind turbine. Then, the noise level on the ground has been predicted including the effects of air absorption, ground reflection and diffraction.

대형 풍력발전기 소음원 분석

Wind turbine noise become main environmental problem as wind energy have been installed all around. Noise from large wind turbine give annoyance to listener, moreover it increase loading to whole system by restricting blade tip speed. However accurate noise mechanism of wind turbine is not yet examined. This paper reviewed noise source and analysis theory. Broadband noise if main component of wind turbine noise and airfoil self noise is main noise source. These make acoustic analogy hard to apply for analysis. For this reason, experimental equation is method for wind turbine noise prediction up to now. Spectrum analysis shows that vortex shedding noise exists around Hz. This region is most sensitive frequency range to human. Thus it is necessary to reduce this noise source.

An overview of the acoustical activities at the National Wind Technology Center.

The National Wind Technology Center (NWTC) has been involved in wind turbine acoustics since the 1980s. The areas of work include standards development, measurement and analysis, prediction code development, and acoustic arrays. Most measurements are conducted to the IEC 61400‐11, a standard specifically for acoustic measurements of wind turbines. The NWTC is involved in the development of this standard. The standard results in reports of overall levels as well as tonality. The NWTC has also developed a semiempirical acoustic noise prediction code for wind turbines. Validation of this code with test data (both wind tunnel and field measurements) shows reasonable prediction accuracy for both airfoil self noise and turbulent inflow noise. Lastly, to assist with wind turbine noise reduction and to identify the loudest components an acoustic array was developed to better locate noise on wind turbines. This paper will describe the NWTC’s past and current activities in wind turbine acoustics including test methods and results.