Numerical Simulations Of The Near Wake Around The Wind Turbine Nacelle

During the operation of wind turbines,wind velocity measurement mainly relies on the anemometer above the nacelle.The flow around the nacelle anemometer is influenced by the natural inflow,wind rotor surrounding flow and the attach equipment on the nacelle.The measurement velocity is different from that far before the wind turbine,which is to be calibrated by the nacelle transfer function.And the transfer function is close related to the near wake flow field along the downstream of wind rotor.Hence,the analysis of the nacelle near wake flow field is significant.A 2MW wind turbine is selected to carry out the steady and unsteady numerical simulation on the near wake flow around the nacelle.The aerodynamic performance at different azimuth angles at the 9m/s velocity are validated with the design results.The characteristics of the flow field near the nacelle are analyzed.The aerodynamic performance and flow field characteristics near the nacelle among the low velocity of 5 m/s,13 m/s high velocity and typical wind velocity of 9 m/s are investigated.The variation of the nacelle flow field and anemometer measurement results are investigated under the different radiator geometric shapes above the nacelle and the radiator with jet flow.Based on the study of uniform inflow,the sinusoidal time-varying inflow is studied,and the fluctuation variation of wind speed caused by the nacelle wake flow is analyzed.The steady simulation results show that,the wind velocity fluctuation near the nacelle wall is underestimated due to the historical effect of wake cannot be taken into account.The unsteady calculation results show that,the measurement accuracy of the anemometer can be increased by properly elevating the position of the anemometer.The turbulent intensity near the front of the nacelle increases with the increase of wind velocity,while the turbulent intensity near the tail of the nacelle changes the other way around;Under the same inflow velocity,the turbulent intensity increases first and then decreases along the streamwise,and increases again near the tail of the nacelle.For the radiator model above the nacelle,when the radiator works,it can reduce the influence of the radiator geometric surrounding flow.For sinusoidal time-varying inflow,the mutual influence of the inflow frequency and wind rotor rotation frequency,resulting in the decrease of the power spectrum amplitude and the increase of the flow low frequency harmony signal.When the mixture of the more sinusoidal inflow,the amplitude become lower and more low frequency harmony signals,leading to the more complex flow around the nacelle.The flow around the nacelle is influenced by the unsteady inflow velocity.With the increase of the nacelle velocity,the diffusion velocity of high energy fluid become higher at the tail of the nacelle.