| In order to optimize the aerodynamic characteristics of the downwind wind turbine,this thesis designed a wind turbine imitating the seal whisker tower(bionic tower for short).The wind tunnel test method was adopted to carry out the aerodynamic characteristics of the bionic tower as well as the power characteristics and wake characteristics of the downwind bionic tower wind turbine.Meanwhile,the aerodynamic performance and wake characteristics of the bionic tower and the aerodynamic load and power increase mechanism of the downwind bionic tower wind turbine are analyzed by numerical simulation.The main research achievements are as follows:The concept of aspect ratio(AR)is introduced to design three kinds of bionic tower models.The aerodynamic performance and flow field characteristics of bionic tower and cylindrical tower are compared and analyzed by numerical simulation.The results show that compared with the cylindrical tower,the bionic tower suffers smaller drag coefficient and deformation degree and vibration amplitude,the pressure difference between the front and back of the tower is smaller,the velocity recovery in the far wake area is faster,the turbulence is weaker and the vortex street is more easily dissipated,which can effectively suppress the vortex-induced vibration.In the above research,the aerodynamic performance of the bionic tower with AR=1.2 is the best.The wind tunnel test method is used to compare the turbulence intensity and wake wind speed power spectrum density of the bionic tower and the cylindrical tower with AR=1.2.The results show that the turbulence intensity in the flow field of the bionic tower is obviously less than that of the cylindrical tower.The energy distribution difference of wake wind speed in frequency domain is mainly manifested in the near wake region,where the energy amplitude of the bionic tower is smaller than that of the cylindrical tower,and the peak amplitude is also smaller than that of the cylindrical tower,indicating that the bionic tower can effectively suppress vortex-induced vibration.It is worth noting that the frequency of peak signal in the bionic tower is slightly higher than that in the cylindrical tower.Wind tunnel test is used to compare the power characteristics and wake characteristics of two kinds of tower wind turbines at different yaw angles and different distances from the wind turbine to the tower.The power characteristic study shows that the power coefficient difference of each working condition is mainly reflected in the high tip speed ratio segment:the power coefficient of downwind wind turbine is greater than that of upwind wind turbine.At 0° and counterclockwise yaw.the power coefficient of the bionic tower wind turbine is greater than that of the cylindrical tower wind turbine,but the power coefficient of the bionic tower wind turbine is opposite at clockwise yaw.The output power will decrease with the increase of yaw Angle.The study of wake characteristics shows that the bionic tower structure can cause more downwind velocity loss behind the wind turbine wheel,and the bionic tower structure can improve the velocity loss in the vertical range below the wind turbine when yaw is 0° and 15°counterclockwise.The upwind Angle of attack calculated by BEM theory formula shows that the upwind Angle of the bionic tower wind turbine is closer to the optimal Angle of attack when yaw at 0° and 15° counterclockwise,which proves the above research conclusions of power characteristics.With the increase of the flow distance,the turbulence intensity increases first and then decreases.The maximum turbulence intensity is concentrated behind the wind turbine.In the wake zone of the vertical range below the wind turbine,the turbulence intensity of the downwind bionic tower wind turbine is obviously less than that of the downwind cylindrical tower wind turbine.In addition,different yaw angles have obvious effects on turbulence intensity distribution.By numerical simulation,the aerodynamic load,output power,surface pressure distribution and pressure field variation of two kinds of tower downwind turbines under different tip speed ratios were studied.The results show that the thrust.torque and power decrease rapidly due to the blocking effect of the tower,and the lowest value is reached when the blades are just swept downstream of the tower.With the increase of tip ratio,the thrust force on the blade increases continuously,while the torque increases first and then decreases.The downwind bionic tower wind turbine is beneficial to increase the blade surface pressure difference,thrust and torque,so as to effectively improve the output power,while reducing the load and power fluctuations,which has the advantage of improving the aerodynamic characteristics of the wind turbine. |
PDF Full Text Request