Wake Distribution Of Double Horizontalaxis Tidal-current Turbine

Based on CFD(Computational Fluid Dynamics)three-dimensional numerical simulation method,the wake characteristics of a double horizontal axis tidal current turbine is studied.The study of its wake characteristics is also of guiding significance to the arrangement of several turbine airports.This paper summarizes the main research results of single turbine,double turbine and multi-turbine wake at home and abroad up to now.A complete CFD numerical simulation method for studying the wake distribution of twin-turbine is established,which includes the whole process from the geometric model establishment to the grid generation and numerical calculation settings.The applicability of the semi-empirical formula of the outflow velocity of the transverse-axis tidal current energy turbine to the double-transverse-axis tidal current energy turbine has been verified.According to the wake lateral velocity distribution equation of a single turbine,the velocity prediction equations suitable for the zone of flow development(four valley value)and zone of flow development(two valley value)within a double turbine are proposed.According to the CFD results,the minimum velocity variation formulas for different outlet planes are modified.The applicability of the theoretical equations for predicting the wake of a double horizontal axis tidal current turbine are discussed by comparing the calculated results with CFD numerical simulation and previous experimental results.Comparing the wake of double horizontal axis tidal current turbine with that of single horizontal axis tidal current turbine,the phenomenon of double valleys in the region near the blade can still be observed,and the phenomenon will gradually disappear with the development of the wake.The wake of a double horizontal axis turbine will converge at a certain point with the development of the turbine.This convergence will accelerate the wake in the middle area and the wake will decay as a whole.Because the length of the wake domain is limited,the wake is not completely recovered in the range of 30 D.The distribution of axial,radial and tangential velocity components in the outflow plane of a double horizontal axis tidal current turbine wake and their variation with the wake are studied.Referring to the different rotating directions of the propeller,the wake distribution of four kinds of double horizontal axis tidal current turbine with different rotating directions is discussed.The effect of different rotational directions on the minimum velocity of the outlet plane is not obvious,but it has a direct impact on the position of vortex cluster behind the blade.The intersection point of two turbine wakes at different blade spacing is studied.It is found that the intersection only occurs at smaller blade spacing.The effects of four airfoils on wake outflow velocity,tip velocity ratio on wake outflow velocity,tip velocity ratio on turbulence intensity,and the effects of blade spacing and tip velocity ratio on the length of wake independent region were studied by CFD numerical simulation.The results are compared with the numerical simulation of single turbine and the results of previous experiments.The wake turbulence intensity distribution of double transverse axis tidal current turbine is studied,and the distribution characteristics of axial,radial and tangential components are discussed.