| In the fields of aerospace and fluid machinery,because of the existence of airfoil resistance and aerodynamic noise,the comprehensive energy utilization rate is usually low.Therefore,it is necessary to study the flow field control of the airfoil to achieve the reduction of the resistance and the aerodynamic noise.In this paper,according to the shark skin shield scale structure,the two-dimensional function of the single bionic groove is obtained by curve fitting method,and applied to the NACA0012 airfoil surface to establish three airfoil models with bionic grooves.The bionic grooves are respectively arranged in the airfoil 0.35-0.40 times chord length,0.50-0.55 times chord length,0.65C-0.70 C times chord length,and they are respectively defined as Airfoil-H1 airfoil,Airfoil-H2 airfoil and Airfoil-H3 airfoil.In this paper,large air eddy simulation is used to simulate the airfoil with three bionic groove structures,and the mean pressure coefficient distribution,mean wall shear stress distribution,mean normal velocity distribution,the velocity cloud diagram,the streamline diagram and the vortex structure are used to investigate the influence of the bionic groove structure and it's position on the flow characteristics and aerodynamic characteristics of the airfoil at 6° angle of attack,24m/s and 30m/s.The angle of resistance ratio explores the drag reduction effect of the bionic trench str ucture.The results show that the Airfoil-H1 airfoil drag reduction rate reaches 16.99%,the lift-to-drag ratio increases by 16.34%,the lift coefficient only decreases by 3.43% at 24m/s.And the Airfoil-H2 airfoil drag reduction rate reaches 18.09% at 30m/s,the lift-to-drag ratio increased by 18.86% and the lift coefficient decreased by only 2.63%.This is because the Airfoil-H1 airfoil and the Airfoil-H2 airfoil effectively reduce the separation zone range,allowing the fluid to reattach as early as poss ible at the trailing edge of the airfoil and reducing wake flow losses,thereby returning fluid to good flow characteristics.When the fluid velocity is increased from 24m/s to 30m/s,it can be found that the airfoil with the best aerodynamic performance is gradually transitioned from the Airfoil-H1 airfoil to the Airfoil-H2 airfoil,indicating the position of the bionic groove arrangement and fluid velocity has an optimal match value.Improvements in the flow characteristics of the airfoil surface can have a certain effect on its aerodynamic noise.In determining that the bionic groove structure can improve the flow characteristics of the airfoil,and has a good drag reduction effect,the airfoil is predicted by the LES+FW-H method,from the instantaneous sound pressure,the sound pressure level at the receiving point,and the power spectral density,the total sound pressure level and other angles explore the influence of bionic groove structure on airfoil aerodynamic noise.And the noise reduction mechanism is analyzed from the perspective of pulsating pressure cloud map and vorticity cloud map.The results show that at the 6° angle of attack of 24m/s,the Airfoil-H1 airfoil sound level is reduced by 4dB and the total sound pressure level is reduced by 3.83 d B,which is 7.76%.This is because the Airfoil-H1 airfoil weakens the airfoil surface pressure pulsation,and the height of the airfoil surface vorticity band is significantly reduced,and the vorticity band of the trailing edge is significantly narrowed,which reduces the airfoil surface boundary layer-vortex shedding noise.The Airfoil-H2 airfoil has no obvious noise reduction effect,and the Airfoil-H3 airfoil will increase the airfoil aerodynamic noise.Finally,the existence of the internal vortex of the groove is verified by experiments.It is confirmed that the direction of the fluid flow in the top of the vortex is consistent with the direction of the main motion,which acts like a “rolling bearing”,so that the fluid in the boundary layer is weakened by the viscous resistance of the wall and eventually reduce fluid energy dissipation. |
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