Study On Drag Reduction Characteristics Of Airfoils For Wind Turbine With Microstructures On Surface

Studies of drag reduction and lift enhancement by microstructures on airfoil have great significance both to improve aerodynamic performance and increase rotor power coefficient, which finally enhance generating efficiency. The simple and effective technology will make huge contribution to the long-term development of wind power.Based on existing smooth airfoil experiments for DTU-LN221 and Ris(?)-A1-21 designed for wind turbine, combined with theoretical analysis, ANSYS Fluent software with Transition SST turbulence model is used for numerical simulation of the airfoils. Verification for independence of grid and reliability of numerical calculation lays the foundation for further studies of microstructure on surface.SST k-ω turbulence model is used for hybrid grids of airfoils with microstructure. Layout position, size and shape of microstructures on DTU-LN221 airfoil are studied. V-microstructures with size of 0.13mm and angle of 56°decorated before 0.6c on suction side can obtain a certain lift enhancement at high angle of attack. Microstructures without distance are better than those with distance.Layout position, size, length, groove or riblet, AOA and Re of microstructures on Ris(?)-A1-21 airfoil are studied. Maximum drag reduction rate is 16.224%, and maximum lift enhancement is 14.796%. V-grooves at the back Within the scope of suction side is better. Pressure side with grooves is better than one without grooves. Drag reduction and lift enhancement are less affected by closed sizes or lengths. When difference between lengths is large, the longer one can obtain larger drag reduction and lift-drag ratio enhancement, but smaller lift and moment enhancement. Groove and riblet with same size and length can obtain similar effects. Before stall, effects of drag reduction and lift enhancement increase with AOA, besides, lift and moment enhancement decrease with increase of Re, but drag reduction and lift-drag ratio enhancement increase.Mechanisms of drag reduction by effective microstructures on the two airfoils are studied from 6 aspects, like viscous and pressure components of drag or lift, pressure coefficient, velocity distribution, wall shear stress, turbulent kinetic energy and turbulence dissipation rate. The pressure components of drag or lift plays a decisive role to the total value. Effective microstructures increase integral area of pressure coefficient, which lead to increases of lift coefficient. Effective microstructures keep the air into the structures forming "micro air bearings" to raise the boundary layer, what’s more, the structures reduce the energy within the boundary layer and decrease thickness of boundary layer after that, which are essence and mechanisms of the drag reduction by microstructures.