Influence Of Turbulence On Aerodynamic Characteristics Of Wind Turbine Airfoil

Incident flows on wind turbines are often highly turbulent.The existence of turbulence will have a significant impact on the aerodynamic performance of wind turbines.Wind turbine blades are composed of numerous airfoil sections,so it is of great importance to study the aerodynamic characteristics of wind turbine airfoils in turbulence.Fluent software with large eddy simulation(LES)method is used to verify the flow field of Tongji University 6×5×05 grid.The comparisons between test and calculation results show that the turbulence intensity distribution of grid-generated flow field agrees well with each other,which proves that the calculation method is suitable for predicting grid-generated flow field.Based on this method,the flow field generated by 4×8×03 grid is predicted.The calculation results show that the calculated flow field is in accordance with the decay laws of turbulence.At the distance from the grid 1?2 m,the turbulence intensity range is about 8%?10%,which is in line with the requirements of the airfoil test in the turbulent condition.The flow field of five different grids is measured by hot wire anemometer in the wind tunnel.The results show that the influence of different wind speeds on the turbulence intensity and the turbulence integral scale is small.The turbulence intensity in the flow field decreases with the increase of distance,and the trend of the turbulence integral scale is opposite.Turbulence intensity decreases a bit with the gap between bars decreases.When the width of grid bar widens,the turbulence intensity and integral scale will increase significantly.Adding transverse bar will increase turbulence intensity and reduce integral scale.The analysis of typical grid flow field of turbulent power spectral density shows that the measured power spectrum in wind tunnel is in good agreement with Karman spectrum.The power spectral density decreases with the increase of the grid distance,and increases with the increase of turbulence intensity and wind speed.The power spectrum characteristics of fluctuating wind in different directions are the same.The experiments of DTU-LN221 airfoil under different turbulent conditions are carried out in wind tunnel.When turbulence is less than 0.5%,with Reynolds number changes from 5.0×10~5 to 1.4×10~6,lift coefficient changes very little and drug coefficient decreases gradually,resulting in the increase of the maximum lift resistance ratio as Reynolds number increases.Reynolds number has little influence on the aerodynamic performance of airfoil When turbulence is greater than 9%.Comparing the aerodynamic characteristics of airfoil in different turbulent conditions,it is found that the stall angle of airfoil is delayed from 12.4° to 17.4° in high turbulence level,and lift coefficient is obviously improved,and the maximum lift coefficient is up to 1.953 when turbulence intensity is 19%.Drag coefficient increases with the increase of turbulence intensity,and the trend of moment coefficient is opposite.Lift drag ratio decreases significantly with the increase of turbulence intensity in main attack angle area.The increase of turbulence integral scale leads to the increase of the maximum lift coefficient and the increase of drag coefficient,and the lift drag ratio will decrease.The influence of pressure fluctuation on the lift coefficient of airfoil increases with the increase of attack angle,and the most obvious is in the stall area.In general,aerodynamic performance of airfoil will decrease significantly in high turbulence level.It can be seen from analysis of pressure coefficient distribution on airfoil surface,the influence of turbulence on aerodynamic characteristics of airfoil is attributed to the change of flow state on airfoil surface,and turbulence postpones the occurrence of flow separation.