Study And Application Of Numerical Simulation Method For Wind Turbine Wakes Based On Vortex Dynamics

Offshore wind energy has become one of the most promising renewable energy due to its high energy density and stability.With the development of offshore wind power,offshore multiple wind turbines system as a kind of offshore wind energy utilization technology has gradually attracted the attention of researchers.Aerodynamic interference between wind turbines is an unavoidable problem in the design of onshore and offshore wind farms and multiple wind turbines system.This aerodynamic interference mainly comes from the wake effect.The disturbing of the wind turbine on the flow field results in a wake region with significantly changed flow characteristic.The downstream wind turbine running in the wake region will face a completely different inflow condition from the upstream wind turbine,thus showing completely different aerodynamic performance.Therefore,the accurate simulation of the wind turbine wake is the basis and premise for solving the aerodynamic interference problem.At present,the research on the wind turbine wakes focuses on the far wake,which is also the area of concern for the aerodynamic interference problem of onshore and offshore wind farms.However,for the Multiple Unit Wind Turbine(MUWT)with a relatively compact layout,the aerodynamic interference often occurs in the near wake,so common analytical wake models are no longer suitable for this problem,and the universal CFD technology is usually accompanied by huge computational requirements.Therefore,there is an urgent need for an efficient and accurate wind turbien wake simulation method suitable for the whole wake.This is also the initial motivation of the study work in the present paper.For the problem of vorticity concentration,such as the wind turbine wake,the vortex method in Lagrangian-frame has great advantages in numerical calculation.This paper attempts to construct wind turbine wake simulation methods using vortex method combined with blade element momentum(BEM)theory.The main idea is to calculate the wake velocity field indirectly by simulating the vorticity evolution in the wake under Lagrangian-frame,and construct a simple method to deal with the disturbing of the wind turbine on the flow field based on BEM theory,so as to avoid discussing the complex boundary conditions on the wind turbine blades in order to improve the computational efficiency.In addition to establishing an efficient and accurate numerical algorithm to investigate the aerodynamic interference of wind turbines,this paper also attempts to re-examine the wake phenomenon and give a concise description of the wind turbine wakes from the perspective of vorticity.The two discrete elements in the vortex method,the vortex partical elment and the vortex filament elment,are used to implement the above ideas.From the results,the numerical methods established by these two discrete elements can meet the initial requirements,while the latter shows better simplicity and efficiency.First,a numerical simulation method of wind turbine wakes based on the vortex particle method and BEM theory is proposed in this paper,in which the disturbing of the wind turbine on the flow field is replaced by a vortex generator which continuously releases vortex particles into the flow field,and the specific configuration of the vortex generator can be obtained by BEM theory.This method of handling wind turbine rotors can be called the Lagrangian generalized actuator model.The reliability of the numerical simulation method of wind turbine wakes is verified by a wind tunnel test,and the results show that the method has acceptable accuracy and higher computational efficiency than the usual CFD method in Eulerian-frame.On the basis of previous work,a numerical wake model of wind turbines based on vortex filament method is constructed by replacing the vortex particle element with the vortex filament element,and the steady state solution scheme is used to further improve the calculation efficiency.Numerical results show that the wake model has good accuracy and high efficiency in the whole wake.In addition,based on the model,a wake analysis framework with vortex filament geometry is established.Under this framework,the vorticity description shows great advantages in explaining the evolution of the wake deficits and analyzing the similarity of wakes.The wake model based on the vortex filament method has high computational efficiency and shows good calculation accuracy in both the near-wake and far-wake.In the last part of this paper,the model is used to investigate the aerodynamic characteristics of dual turbines under different arrangement and the aerodynamic interference problem of a multiple wind turbines system,and a fast method to estimate the aerodynamic performance of the wind turbine running in wakes is proposed.