Research On The Influence Of Dimples Structure On The Aerodynamic Noise Of Wind Turbine Airfoil

Compared with traditional energy,wind energy is a clean and pollution-free renewable energy source,and it is valued by countries all over the world.However,with the rapid development of the wind power industry,the issue of wind turbine noise radiation has also attracted more and more attention.In order to reduce the impact of noise on the structure of the blade itself and the environment,it is very necessary to design low-noise blades.The airfoil is the basic unit that constitutes the blade,and the research on airfoil noise reduction will help the design of low-noise blades.Based on the correlation between flow and noise,Using flow control is an effective way to control noise.The dimples structure was first used for flat plate flow control,which has the functions of reducing drag and enhancing heat transfer.In terms of airfoil flow control,there are currently problems such as unclear applicable working conditions,so the influence of dimples structure on airfoil aerodynamic noise needs to be studied in depth.This paper applies the dimples structure to the airfoil surface.First,the large eddy simulation(LES,Large Eddy Simulation)is used to analyze the flow around NACA4415 under different Reynolds numbers and the airfoil with dimples arranged on its surface.The unsteady state calculation of the flow field is carried out,and the working conditions in which the dimples structure has a better control effect on the flow separation are determined by comparing the results of the flow field.In order to further reveal the influence of the structural parameters of the dimples on the flow,the dimples with different structural parameters are selected and arranged on the smooth airfoil surface under specific working conditions,and the flow control principle and the influence of the structural parameters on the flow separation are analyzed.Use the FW-H equation of acoustic analogy to predict the aerodynamic noise of the smooth airfoil and the airfoil with dimples of different structural parameters arranged on the surface,obtain the sound field information and analyze the noise characteristics,and study the dimples The influence of structure on airfoil aerodynamic noise.Through the above research,it is found that at low and medium Reynolds numbers,the dimples structure can weaken the laminar separation phenomenon that occurs and reduce the separation vortex near the trailing edge;arrange the dimples structure at the position containing the separation point to make the reattachment Compared with the smooth airfoil,the separation area is reduced by about 25% of the chord length;the dimples structure can reduce drag and improve the lift-drag ratio.At the separation point of laminar flow,the depth-to-diameter ratio h/d= 0.15,the lift-to-drag ratio of the airfoil is the largest and the aerodynamic performance is improved.Also when the separation point is included and the depth-to-diameter ratio h/d=0.15,the sound pressure level value in the7.5k Hz～14k Hz frequency band is lower than the sound pressure level value and pressure pulsation in the smooth airfoil and the sound pressure level directivity distribution graph The area is the smallest,and the maximum difference between the sound pressure level of the smooth airfoil and the smooth airfoil is 4.25 d B,dimples has a certain noise reduction effect.This paper provides a new idea for the flow separation and noise control method of the airfoil under the conditions of low Reynolds number and small angle of attack,and provides a reference for related research.