Research On Power Generation Enhancement Mechanism And Arrangement Strategy Of H-type Vertical Axis Wind Turbine Array

With the development of wind energy in the direction of more complex application types such as deep sea,sandy desert,urban environment,and multi-energy complementarity,vertical axis wind turbines have gradually gained widespread attention.This work focuses on the low aerodynamic efficiency of vertical axis wind turbines.From the perspective of multi-unit array wake power enhancement,this paper takes a small straight wing vertical axis wind turbine with three bladed validated by wind tunnel experiments as the main object,and analyzes the aerodynamic load and wake structure of the vertical axis wind turbine under different tip speed ratios,spacing and arrangement schemes.The main research contents are:（1）The three-dimensional aerodynamic performance CFD numerical model of H-type vertical axis wind turbine based on IDDES model of SST model and structural grid technology was established to analyze the aerodynamic characteristics of H-type vertical axis wind turbine under variable tip speed ratio.The results show that,under the conditions of different tip speed ratios ranging from 1.817 to 3.375,the deviation of wind power utilization coefficient calculated by numerical calculation and wind tunnel experiment value is less than 9.5%.The wind energy utilization coefficient of the vertical axis wind turbine reaches the highest value of0.3348 at the tip speed ratio of 2.625.In terms of load,the load of the wind turbine follows the change law of 3f_c,6f_c,and 9f_c,while the load of a single blade follows the change law of f_c,2f_c,and 3f_c.As the tip speed ratio decreases,the power spectral density of the wind turbine load increases,up to a maximum of 5.11%.（2）The zonal characteristics of wake of vertical axis wind turbine are analyzed and the influence mechanism of different tip ratios on wake characteristics is clarified.The results show that under different tip ratios,the wake of a vertical axis wind turbine has two regions:a stable diffuse section and an unstable wake meandering section.When the blade tip speed ratio is relatively large,the vortex characteristics in the wake due to the rotor rotation make a major contribution to the development of the wake,and the wake meandering section is longer.When the blade tip speed ratio is relatively small,the inertial force from the mainstream dominates,and the stable diffusion section of the wake is longer,and the maximum amplification is about0.9 times.When the tip speed ratio is further reduced,the asymmetry of the wake region is significantly enhanced,and the position of the maximum loss of wake velocity gradually moves upward.Under the condition of small tip speed ratio,a stall state will occur in the local stroke of the vertical axis wind turbine blade,and then a large-scale shedding vortex structure will be generated.This vortex structure will strongly interfere with the vertical axis blades traveling downstream,and cause the torque curve of the wind turbine to present a significant fluctuation feature,and the maximum fluctuation intensity of the torque power spectrum integral is increased by 5.11%,which will affect the stability of the wind turbine load output and operational safety.（3）The mechanism of rotating power increase of parallel vertical axis wind turbines was studied,and the rule of influence of rotation direction on wake interference and power output characteristics of vertical axis wind turbines was revealed,and the influence of different tip speed ratios and parallel spacing on the power increase effect of vertical axis wind turbines was studied.The double vertical wind turbine arrays under two modes of counter-rotation in forward flow（Counter-rotating Turbine Rotor,CTR）and counter-rotation in counter-current（Counter-rotating Turbine Rotor Against the flow direction,CTR-A）are analyzed.It was found that the CTR rotation mode can increase the average wind energy utilization coefficient by 8.96%at TSR=2.625,which is mainly due to the jet acceleration effect caused by the reaction force of the blade airfoil lift and drag to the flow field.The vertical axis wind turbine has a power increasing effect in a large range of blade tip speed ratio and a wide range of parallel spacing.The smaller the distance,the more obvious the power increase.This is mainly because when the distance is small,the interference between the rotation effect of the wind turbine and the wake is stronger,so the jet speed-up effect is more significant.The wind energy utilization coefficients were 8.96%,7.46%and 6.57%higher than the reference value in the interval range of 2D to 2.5D,respectively.（4）The effect of vortex street on the aerodynamic efficiency of vertical axis arrays was studied,and the mechanism of vortex street interference effect on aerodynamic characteristics was revealed,so as to improve the power output of vertical axis wind farms under multi-wind turbine arrays.The numerical simulation of the turbine cluster array containing multiple vertical wind turbines was simulated,and it was found that the multi-level wake superposition effect in the wind turbine cluster is an important factor restricting the overall aerodynamic performance of the vertical wind turbines.The aerodynamic performance of the staggered counter-rotating array,array A arrangement,is about 10.8%higher than that of the side-by-side counter-rotating array,array B arrangement at TSR=2.625.The reason is that,on the one hand,the counter-rotating wind turbines in array A produce a jet acceleration effect similar to the vortex street,which promotes the recovery of the wake in the nearby flow area.On the other hand,the maximum loss area of the wake in array A is affected by the jet flow and the rotation effect of the wind turbine,and is deflected to the outer mainstream area,which makes the low-velocity fluid in the wake and the high-speed fluid in the mainstream exchange momentum,and promotes the recovery of the wake.（5）Based on the above numerical research results,this paper gives the basic strategies and suggestions for the actual cluster arrangement of vertical axis wind turbines.The distance H_ctrbetween the two rows of wind turbines in each vortex street power enhancement unit is recommended to be at least 2.0D,so as to have power enhancement benefits under more wind direction conditions.The distance H_str between two wind turbines in the mainstream flow direction is recommended to be more than 10D,and the distance between two rows of wind turbines in staggered arrangement is about 0.5H_str.The distance H_array between two vortex street power enhancement units is at least twice the distance of H_ctr.The research results of this paper are helpful to improve the aerodynamic efficiency of the vertical axis wind turbine array,and also contribute to the micro-site selection and layout optimization of the actual vertical axis wind turbine cluster.