A METHOD FOR PREDICTING AERODYNAMIC NOISE FROM HAWT Alexandru DUMITRACHE * Horia DUMITRESCU * * Institute of Statistics and Applied Mathematics, Bucharest dalex@ns.ima.ro The aim of this paper is to give a new prediction model for the aerodynamical generated noise from horizontal axis wind turbines (HAWT). Aerodynamic noise is generated when the rotor encounters smooth flow. It contains airfoil self-noise and turbulence inflow noise. The present semiempirical model is coupled with CFD and aerodynamic calculation so as to improve the accuracy of the prediction model. By doing CFD computations, boundary layer parameters for some relevant airfoil profiles are stored as a database which is used directly for the noise prediction model. The total noise spectrum for a given wind turbine is compared with experiment and encouraging result is obtained.. Key words: airfoil self-noise, wind turbine noise, Lighthill’s acoustic theory 1. INTRODUCTION The future of using wind energy is so exciting that it has many advantages such as: no air pollution, no need of any fossil or nuclear resources during operation. But with the fast increase of wind energy development, it also gives rise to the problems concerning public acceptance of wind energy. The noise and visual impact are the main drawbacks. The noise from wind turbines may annoy people who live around. Therefore it's necessary to estimate the noise level in the field where the wind turbines are installed. Generally, the noise from wind turbine is composed with mechanical noise and aerodynamic noise. The mechanical noise is caused by the different operating machine elements which can be reduced efficiently by many engineering methods and will certainly not reduce the power output. However, the way to reduce aerodynamic noise from wind turbines should be studied together with power efficiency. A fully established method to predict the wind turbine noise is still limited. For engineering purpose of use, several semi-experimental noise prediction models are available. Some of the models are originally developed for application on helicopter and aircraft wings. One of the first model was carried out by Grosveld [1] in 1985. In 1981, Viterna [2] applied a method to the low-frequency noise estimation from a wind turbine. Brooks, Pope and Marcolini [3] performed a set of experiments for NACA0012 airfoil sections. However, the aerodynamic and acoustic measurements were only based on NACA0012 airfoil which may not suitable for other airfoil profiles. Therefore, the boundary layer parameters at trailing edge should be calculated instead of using experimental data from NACA0012 airfoil. Unweighted, or linear-weighting, was used in the presentation of data, while the standard regulations, typically used in measuring the acoustic emissing from wind turbines, specify A-weighting, which de- emphasizes frequencies below 1000 Hz and correlates extremely well with human subjective response. 2. NOISE AND SOUND FUNDAMENTALS When the fluctuating pressure in fluids is at the level about 10 -4 times the standard atmospherical pressure, the correspond sound pressure level is up to 120 dB in the normal air condition. This sound pressure level is extremely high which is close to the threshold of pain. The governing equations for the aerodynamic sound generation and propagation are the well-known control equations of fluid dynamics: i) The mass equation; ii) The momentum equation; iii) The energy equation. To express the equation with the dynamic sound pressure, the result is the linear wave equation: