Experimental Study On Performance And Wake Evolution Characteristics Of Dual-wind Turbine

Compared with the traditional wind turbine,the dual-wind turbine has two wind turbines that can absorb more wind energy.The dual-wind turbine with the same power will greatly reduce the diameter of the wind turbine,and the front and rear wind turbines can reduce the unbalanced load of the whole machine,resulting in higher power improvement per unit land area and higher utilization rate of land resources.In this paper,based on the wind tunnel laboratory of Lanzhou University of Technology,the power characteristics,load characteristics,wake velocity characteristics and wake turbulence characteristics of the dual-wind turbine are studied.Through the quality evaluation of the flow field in the experimental wind tunnel,the uniformity and stability of the flow field are evaluated by analyzing the change of the flow field velocity with space and time.The results show that the velocity in the wind tunnel has good stability and uniformity,which is an important basic preparation for subsequent experiments.The experimental platform of the dual-wind turbine was built,and the power of the single wind turbine was measured and verified.Wind tunnel experiments were carried out on three types of twin-wheel wind turbines with area ratios（56%,64%and 87%）to study the influence of different pitch and tip speed ratios on power characteristics.The results show that:（a）the power increases of dual turbine wind turbines with different area ratios are 54%,61%and47%respectively for single turbine wind turbines.（b）With the increase of the blade tip ratio of the rear rotor,the total power of the front and rear rotor decreases.（c）With the increase of area ratio,the power ratio of the dual wind turbine shifts to the front wind turbine.（d）The power of the double-wind turbine.With the increase of the distance between front and rear wind turbines,the power reaches the maximum near the distance of 0.2d.（e）The increase of blade tip ratio of the front rotor has an inhibitory effect on the power of the rear rotor.The increase of blade tip ratio of rear turbine with area ratio of 64%promotes the power of front turbine,while the increase of blade tip ratio with area ratio of 56%and 87%mainly inhibits the power of front turbine.Wind tunnel experiments were carried out on three types of double-turbine wind turbines with area ratio by using six-component force balance to study the effects of different spacing between front and rear wind turbines and different tip speed ratios on load characteristics of dual-wind turbines.The results show that:（a）Due to the antirotation movement of the front and rear wind wheels of the double-wind turbine,the forces generated by the transverse force Fy,the longitudinal force Fz,the overturning moment Mx and the yawing moment M_yare in opposite directions,and they cancel each other to some extent.（b）The thrust size of the dual-wind turbine is influenced by the rear wind turbine more than the front wind turbine;The yaw moment Mz of the three types of double wind wheels has little change with the increase of wind speed.（c）With an area ratio of 56%,as the distance between front and rear wind turbines increases,the thrust Fx decreases,the transverse force Fx increases,and the longitudinal force Fz also increases.The overturning moments Mx,M_yand yaw moment Mz all decrease,which improves the stability of the dual-wind turbine to some extent.（d）With an area ratio of 64%,the load force and load torque of the dual-wind turbine decrease with the increase of the spacing,and the operation of the dual-wind turbine is more stable.（e）For the 87%area ratio of the dual-wind turbine,except for the longitudinal force Fz,the forces and torques increased,and the operation stability of the wind turbine decreased.（f）For a wind turbine with an area ratio of 56%,the blade tip ratio of the front rotor increases,the transverse force F_x2and overturning moment Mx₂of the rear rotor increase,and the remaining load force and moment decrease;When the blade tip ratio of the rear rotor increases,the load force and torque of the front rotor decrease.For the 64%wind turbine,the blade tip ratio of the front rotor increases,while the force and torque of the rear rotor decrease.The blade tip speed ratio of the rear rotor increases,while the thrust force Fx₁,transverse force Fy₁,overturning moment Mx₁and overturning moment My₁of the front rotor increase to some degree.The blade tip ratio of the front rotor increases,while the load force and torque of the rear rotor decrease for the 87%area ratio of the double-wind turbine.The blade tip speed ratio of the rear rotor increases,while the load force and torque of the front rotor decrease.Through the combination of pitot tubes and pressure scanning valves,wind tunnel experiments were carried out on three types of dual-wind turbines with area ratios,and the influence laws of wake characteristics under different spacing of front and rear wind turbines and different blade tip speed ratios were studied.The results show that:（a）The wake velocity characteristics of dual wind turbines with different area ratios are greatly affected by the rear rotor.（b）As the distance between front and rear wind wheels increases,the loss of near wake velocity decreases and the influence on far wake velocity is relatively low.（c）For a dual-wind turbine with an area ratio of56%,the tip speed ratio of the front rotor increases,the maximum speed loss point moves forward,and the wake velocity recovers to a certain extent.The recovery of the far wake velocity is less affected by the tip speed ratio of the front rotor.In the case of64%and 87%area ratio,the tip speed ratio of the front rotor increases,and the velocity loss of the near wake increases,while the velocity recovery of the far wake increases to a certain extent.（d）The blade tip speed ratio of the rear rotor increases,and the recovery efficiency of the near wake velocity increases,while that of the far wake velocity also increases.The turbulence intensity was analyzed by measuring the transient velocity,and the results showed that:（a）the turbulence intensity of the near wake was mainly affected by the rear wind turbine,and the turbulence intensity of the dual-wind turbine wake with area ratio of 56%and 87%was greater than that of the wind turbine with area ratio of 64%.（b）With the increase of the distance between front and rear wind wheels,the turbulence intensity near the center of the wake decreases obviously,and the turbulence intensity at the blade tip of the wind wheel increases obviously.With the backward development of the wake,the influence of the distance on the turbulence intensity of the wind wheel wake decreases gradually.（c）For the dual-wind turbine with 56%and 64%area ratio,the turbulence intensity near the wake increases as a whole when the tip velocity ratio of the front rotor increases,while the turbulence intensity of the far wake decreases due to the change of tip velocity ratio of the front rotor.For the wind turbine with 86%area ratio,the tip velocity ratio of the front rotor increases,and the turbulence intensity near the wake center increases first and then decreases.The turbulence intensity at the tip of the rotor decreases,and the influence of the tip speed ratio of the front rotor on the turbulence intensity of the far wake decreases.As the tip velocity ratio of the rear rotor increases,the turbulence intensity near the wake increases,while the influence of tip velocity ratio of the far wake on turbulence intensity decreases gradually.