| Wind turbines operate in a complex atmosphere all year round,often accompanied by the rapid change of wind direction and wind speed,so that the wind wheel can't face the wind in time and is in a yaw operation state.In yaw operation,the effective contact area between wind wheel and wind decreases,and the ability to capture wind energy decreases,which makes the actual output power of wind turbine decrease.Therefore,it is of great significance to study the aerodynamic characteristics and wake field characteristics of wind turbine in yaw state.In this paper,through the field test and numerical simulation of 33 kW horizontal axis wind turbine with two blades,the aerodynamic characteristics and near-wake field structure characteristics of the wind wheel operated under different yaw angles were obtained.The surface pressure distribution,blade surface streamline characteristics,wake characteristics and the three-dimensional rotation effect of the wind wheel had studied at the wind wheel blades under experimental conditions.The effects of yaw angle on the wind wheel aerodynamic characteristics and wake field structure were analyzed.?1?Numerical simulation of wind turbine based on experimental conditions of blade surface pressure measurement.The external field experiment platform was used to measure the blade surface pressure,incoming flow,and the operating parameters of the wind turbine,and the numerical simulation of the experimental conditions was performed on the wind wheel.The pressure distribution of blade surface,streamline of blade surface,velocity and turbulence characteristics of wake zone was analyzed.The study found that the pressure difference from the blade tip to the root of the blade increased first and then decreased.The numerical calculation results of the#1to#4 airfoil coincided well with the experimental pressure distribution curve.The predictive ability of the unsteady characteristics caused by the scale separation flow was limited,which caused a large deviation between the experimental results of the#5 to#7 airfoil pressure distribution near the blade root and the calculation results.Under this working condition,a large area of flow separation occured on the suction surface of the blade,and the flow separation range was larger as it gets closer to the blade root.A study of wake characteristics found that the wind turbine wake was tilted under this condition;the speed loss was the most serious at 1D,and the speed recovered at 6D to 87.4%of the axial component of the incoming wind speed as the vortex develops downstream;the vortex volume at the center of the vortex core decreased,and the radius of the vortex core increased;at 1D,the turbulence intensity reached 5.4×10-2.With the increase of the distance from the wind turbine plane,the turbulence intensity gradually decreased,and at 6D the intensity was 2.1×10-2.By comparing and analyzing the velocity and turbulence distribution on both sides of the wake centerline,it was found that there is obvious asymmetry on both sides of the wake.?2?Study on the three-dimensional blade rotation effect under experimental conditions.Based on the numerical simulation of the experimental working conditions,the two-dimensional numerical calculation of the corresponding inflow of the 7 blades corresponding to the airfoil is carried out.By comparing and analyzing the second and three-dimensional calculation results,the three-dimensional rotation effect of the wind wheel is studied.By comparing and analyzing the airfoil pressure distribution and lift characteristics,it is found that due to the effect of the three-dimensional rotation effect,the three-dimensional calculation results of the pressure difference and lift coefficient of the upper and lower airfoil of the airfoil are larger than the two-dimensional calculation results,and the deviation is more obvious at the blade tip and root.At the position where the absolute value of the pressure on the suction surface of the#1 airfoil is the largest,the absolute value of the surface pressure in3D calculation increases by 58.4%compared with that in 2D,and the lift coefficient increases by 22.23%;the surface of the 3D calculation result in the 19.8%chord length of the suction surface of the#5 airfoil The absolute value of pressure is increased by 56.9%compared with the two-dimension,and the lift coefficient is increased by 14.8%;the absolute value of the surface pressure of the#3 calculated surface pressure points of the#6and#7airfoil in front of the suction is increased by 45%and 259.5%respectively compared with the two-dimension,and the lift coefficient is respectively The increase was 24.1%and 87.6%,and the difference between pressure difference and lift was most obvious at the root of the leaf.At the same time,the three-dimensional effect reduces the flow separation area on the airfoil surface,delays the flow separation,and the separation point moves along the chord to the trailing edge.The#5airfoil delay phenomenon is most obvious,and the separation point lags behind by 12.33%.?3?The effect of yaw angle on aerodynamic load and wake characteristics of wind turbines.By changing the yaw angle of the wind turbine,the influence of the yaw angle on the thrust,torque,power,wake speed and turbulence characteristics of the wind turbine,as well as the pressure distribution on the blade surface and the three-dimensional rotation effect are studied.The study found that as the yaw angle increases,the aerodynamic thrust,torque and power of the wind wheel decrease.When the yaw angle is 45°,the power of the wind turbine drops to 8.1 kW,which is 38.3%lower than that at 0°yaw;As the yaw angle of the wind wheel increases,the energy of the thrust of the wind wheel increases.When the wind wheel operates at different yaw angles,the thrust power spectrum shows a significant peak,and the frequency corresponding to the peak is 1.86 Hz,which is the same as the passing frequency of the blade equal.As the yaw angle increases,the pressure difference between the upper and lower wing surfaces of the airfoil of each section decreases,the pressure distribution near the blade tip is not sensitive to yaw,and the pressure distribution near the front edge of suction is most sensitive to yaw.When the wind turbine is in yaw operation,the airfoil of the same section of the blade has the smallest pressure difference at 0°azimuth angle,the largest pressure difference at 180°azimuth angle,and moderate pressure difference at 90°and 270°azimuth angle,and the pressure difference value is basically the same.As the yaw angle increases,the asymmetry and deflection in the wake area become more obvious.The longer the wake area periodically changes after the wind wheel,the greater the maximum axial speed loss,but the axial speed loss recovers Faster.The turbulence intensity distribution no longer exhibits a symmetrical distribution as the yaw angle increases.The inverted"W"distribution gradually transforms into a single-peak distribution,and the recovery speed of the turbulence intensity is accelerated. |
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