ABSTRACT

In this paper, a wind turbine wake simulation method based on the vortex particle method and BEM theory is proposed. The main idea is that the wind turbine's perturbation effect on the flow field can be regarded as a vortex generator that continuously releases vortex particles into the flow field, and the free evolution of the vortex particles in the flow field forms the wind turbine wake field. The results show that the method exhibits better accuracy in the full field of the wake and has higher computational efficiency compared to the Eulerian CFD method.

INTRODUCTION

The aerodynamic interference between wind turbines (wake effect) is an inevitable problem in the research and design of onshore and offshore wind farms. It is mainly characterized by velocity deficit and additional turbulence, which can be explained as the velocity deficit behind the upstream wind turbine leads to the power loss of the downstream wind turbine, while the increased turbulence leads to the increase of the structural load of the downstream wind turbine and leads to the increase of fatigue damage. Therefore, accurate simulation of wake is the basis and premise to solve the problem of aerodynamic interference.

Previous methods of wind turbine wake simulation have focused on Momentum Balance Method, combining Blade Element Method to form Blade Element Momentum (BEM) Theory (Glauert, 1935); Euler Finite-Volume CFD method (Martinez-Tossas, 2012); Generalized Dynamic Wake Model (Peters and Zhongyang, 2014) and Lagrange Vortex Method (Marten, 2019; Marten, 2020). In recent years, many scholars have also tried to use the Vortex Particle Mesh Method (Chatelain, 2011) and Lattice Boltzmann Method (Wood, 2015) commonly used in the field of fluid mechanics. The BEM theory assumes that the rotor plane is stationary, the floating offshore wind turbine may experience larger oscillation under wave action, and the wake itself may interact with the rotor blade, which is not considered in the Momentum Balance Method. Euler CFD is widely used in wind turbine wake research, most of which adopt DNS (Moin, 1998), LES (Sagaut, 2006) or RANS (Xiao, 2019) method, and there are DES method (Rasam, 2018) combining RANS and LES. In this case RANS is used near the blade surface, to circumvent the prohibitively fine mesh that LES requires near a wall, and LES is used in the unbounded regions. Although the accuracy of the wake simulation is high, it is impractical to generate a large amount of data and computational cost for the design and certification of wind turbine engineering. Compared with the previous two methods, the Lagrange Vortex Method has unique advantages, high precision in the wake near and far fields, and high computational efficiency compared to the usual CFD method based on Euler framework.

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