Numerical Simulation Of Wind Wake Distribution In Complex Terrain Considering Atmosphere Stratification

The development of wind energy resources is an important technology to solve the energy shortage.With the further demand for clean energy in China,the 14 th five year plan proposes to move the wind energy base to the southeast coastal areas.In the southeast coastal areas of China,the hills are densely distributed while the wind speed is low,which puts forward high requirements for the optimal arrangement of wind turbines.Under such terrain conditions and wind speed conditions,the atmospheric stratification effect is significant.Previous studies have studied stratified flow,but there are still some problems as follows: no coupling study with wind turbine;The coupling effect of complex terrain and temperature gradient is not clear;The sensitivity of surface roughness to the wind turbine wake field under atmospheric stratification is uncertain;Lack of wind turbine wake researching on the influence of atmospheric stratification in real terrain.Therefore,it is necessary to study the distribution of the turbine wake field under the influence of atmospheric stratification in complex terrain.In this paper,LES(Large Eddy Simulation)is used to simulate the wake of a turbine in complex terrain.Firstly,according to Boussinesq hypothesis,temperature gradient is added in the form of buoyancy term to explore the influence of wake distribution when a single turbine exists in flat terrain with different atmospheric stratification.Then,the numerical model of typical complex terrain is established to analyze the influence of terrain and turbine coupling on the downstream flow field when atmospheric stratification is different.Furthermore,UDF language is used to add force source term in FLUENT to introduce rough surface conditions to study the distribution characteristics of flow field under the coupling effect of roughness and temperature gradient.Finally,the real terrain model of Guangdong Nan’ao Island wind farm is established,and the real location of wind turbine in Nan’ao Island is selected for numerical simulation,which provides reference for the actual layout of wind farm.The numerical simulation results show that the influence of stratification number on the close wake region is significant: when K= 0,the minimum velocity in the wake region is 0 m/s and the maximum turbulence intensity is 0.5;When K = 1.5,the minimum velocity is-5m/s and the maximum turbulence intensity is 0.6.Atmospheric stratification can also significantly change the wind field distribution in the close turbine wake region: when the incoming wind speed is 5m/s,the turbulence intensity increases by about 0.3 and the velocity loss increases by 2m/s.The existence of roughness weakens the effect of temperature gradient in the wind field: the velocity loss caused by temperature gradient in the turbine wake under rough surface is less 1m/s than under smooth surface,and the influence of temperature gradient on the turbulence intensity in the turbine wake is also reduced under rough surface conditions,even in the range of 0L～ 0.5L,the turbulence intensity decreases due to the influence of temperature gradient.In the case of turbine group,the presence of temperature gradient will increase the wind power of turbine with obvious wake effect.For the turbine with no obvious wake effect,the wind power is reduced under the influence of temperature gradient.