Study Of Wake Characteristics Of Wind Turbines Based On 3D Improved Actuator Surface Model

The wake interaction among wind turbines will decline the efficiency of power extraction and shorten the service life of blades. While, the atmospheric boundary layer (ABL) that the wind turbine works in is in disorder, instability and the flow field of wind turbines is three-dimensional. These bring an important difficultly to the prediction of power extraction under complex operating conditions and even enormous challenge to the study of wind turbine wakes. In this paper, the following studies based on the OpenFOAM platform are done focuses on the wake characteristics of wind turbine and aims at providing useful supply to the aerodynamic performance and the turbine arrangement of wind farm.On the premise of reducing the requirement in quality and number of mesh in traditional CFD methods, the improved actuator surface model is adopted in this paper, This model represents rotor blade by adding equivalent forces that are distributed along the two-dimensional airfoils surfaces, and the surrounding flow field is governed by a full set of N-S equations. Therefore, the number of grid and computing time can be significantly reduced.Firstly, the wake characteristics of wind turbine are studied using the actuator line model as well as the CFD model based on the multiple reference frame under uniform inflow. The comparative results show that:The velocity and enstrophy field of the two models show good consistency, which numerically verifies the viability of ALM model.Then, the computing procedure of independent developed model (improved actuator surface model, IASM) is introduced. The characteristics of wake field based on the IASM model are studied and compared with the results by the CFD model,. The results show that: compared to the ALM model, the velocity field of wake is more close to the CFD results. Contrast of the blade surface pressure distribution of the IASM model, CFD model and data from NREL, the tendency of IASM model has a good consistency with the other two models, and thus numerically validate the accuracy of IASM model.Thirdly, the characteristics of wind turbine under wind shear inflow and wind turbulent inflow are conducted to investigate the influence of wind regime to wind turbine wake field. The results show that:the wind shear field cause the wake to undergo a more unsymmetrical distribution. The velocity deficit above the hub center axes is bigger than at which down the hub, while turbulent flow field is symmetrical distribution. The helical vortex structure in shear flow is visualized unequal interval and in turbulent flow field distinguishing with shear flow is an equidistant helical vortex. Both the two flow field have a thin layer with big speed gradient and vortex sheet.Lastly, for the respect of wind farm:the wake characteristics of wind turbines under different arrangement are studied to investigate the influence of arrangement.The results show that:The interaction effect in the flow field is non-linear added, which accelerates the development so that the flow field structure is quickly broken and reconstructed. Meanwhile, for the wake of different arrangement, the influence of interaction effect on downstream wind turbine of varies. The flow field of staggered turbines develops faster than aligned turbines and the flow field of downstream develops into turbulent with small arranging space more quickly.