| Flat terrain is the ideal terrain for wind farm site selection.However,wind farms in regions with abundant flat wind resources in China have basically been exhausted because of the increasing human demand for clean energy.Onshore wind development has shifted focus to complex terrain.However,complex terrain will lead to large-scale flow separation and flow around the atmospheric boundary layer and will also lead to increased atmospheric turbulence and more complex atmospheric flow structure.This makes it more difficult to accurately assess the state of wind resources.Therefore,Therefore,the accurate analysis and evaluation of the flow field characteristics of wind field in complex terrain will provide a basis for wind farm planning,micro-site selection,wind turbine model selection and load calculation and provide guidance for wind power prediction and maximum utilization of wind energy resources in wind farms.In this paper,the wind field flow on Bolund island was numerically simulated by the method of LeMOS coupled large eddy simulation(LES)based on the experimental results of Bolund island carried out by Ris laboratory.The applicability of LeMOS coupled large eddy simulation(LES)method to generate turbulent wind field in complex terrain is verified By comparing with the measured results.Then the numerical simulation of Nibe B wind turbine in Nibe wind farm is carried out by the method and the actuator disk model and the wake field characteristics of wind turbine in flat terrain are studied.Finally,numerical simulation is carried out for a real mountain terrain wind field to study the flow field characteristics of complex terrain and the wake characteristics of wind turbines in mountain terrain.(1)It is obvious that the velocity pulsation characteristics of the turbulent wind field generated by the boundary coupling large eddy simulation of the inlet of the artificial turbulence.The velocity field has no obvious attenuation in the whole time and the characteristics of average turbulence intensity and turbulence intensity pulsation at different heights in the flow field are well preserved.Numerical simulation of inlet flow conditions in 239 ° and 270 ° directions is carried out for Bolund island.On the characteristic Line of A,the simulated value at 5m is closer to the experimental value than that at 2m and the simulated result of pre-island position is more accurate than that of post-island position.The LeMOS-LES method generates turbulent wind field which is closer to the real atmospheric flow characteristics and can effectively reveal the circumfluence and wake characteristics of the flows around the terrain of Bolund island.(2)When the numerical simulation of Nibe B wind turbine is carried out,the turbulent inlet boundary is used to generate the turbulent wind field closer to the real atmospheric boundary layer.The variation of flow velocity around wind turbine,velocity distribution and turbulence at typical position of wake area are studied.The research shows that the blocking effect of wind turbine leads to the speed reduction in front of the wind wheel.The closer the incoming flow is to the wind wheel,the more obvious the deceleration.At 2D,1D and 0.5d before the wind wheel,the wind speed losses were about 4%,6.3% and 11.8% respectively.The turbulent kinetic energy is large in the wake area above the wind wheel axis.This shows that the mixing effect between the wake area above the wind wheel axis and the main flow area is strong and the wake speed recovers quickly.The mixing effect between the wake area below the wind wheel axis and the main flow area is weak and the wake speed is slow to recover.As a result,the wake center is shifted downward as the wake develops backward.The migration distance is no longer changed about 6D after the wind wheel.The wake expands as the fluid passes through the wind wheel.The acceleration zone between the lower boundary of the wake and the ground is similar to the tapering tube effect and the range of the acceleration zone is about 3D.This region of acceleration compresses the lower boundary near the wake.This compression results in an asymmetry between the upper and lower boundaries of the wake.After 4D,the bottom boundary of the wake coincident with the ground and the extrusion gradually disappeared.Because the brake disc model is used in this paper to replace the real wind wheel,the simulation results are somewhat different from the experimental results.Wake speed recovery ahead.The turbulent wind field generated by LeMOS-LES can simulate the wake flow changes of wind turbines more accurately compared with the simulation results of SST turbulence model coupled actuator disk model.Therefore,it is expected that the wind turbine wake research based on the modified actuator model will be carried out in the following work(3)Based on the terrain characteristics,two wind turbines were arranged at the typical position on the top of the mountain and numerical simulation was carried out on the wind field flow of a real mountain terrain to study the influence of mountain terrain on the wake flow characteristics of the wind turbine.The research shows that the small scale terrain characteristics of mountain terrain have a great influence on the near ground flow,but have no obvious influence on the high altitude flow.The feature of large scale valley in mountainous terrain will cause the feature of horizontal flow around the mountain to be enhanced obviously.The feature of vertical flow around the mountain will cause the wind turbine wake on the mountain top to move down the slope on the leeward side.The feature of horizontal flow around the mountain will "squeeze" the wake of the wind turbine and cause the wake of the wind turbine to be offset.This squeezing effect causes the wind turbine wake expansion rate to be less than flat terrain.Mountain terrain leeward valley(close to the center of the wind wheel)will lead to the increase of the peak near the col of the wind turbine’s wake area in the transverse(y direction)turbulence distribution "double peak effect".(4)By comparing the variation of wake speed loss between wind turbines in mountain terrain and wind turbines in flat terrain,it can be seen that at different locations in the wake area of wind turbines,the wake speed loss of wind turbines in mountain terrain is greater than that of wind turbines in flat terrain.In the range of 2.5d-4d,the recovery rate of wake velocity of wind turbines in mountain terrain is basically the same as that of wind turbines in flat terrain.In the range of 4d-7.5d,the recovery rate of wake velocity in flat terrain is lower than that in mountain terrain.This is because the horizontal flow around the mountain terrain accelerates the mixing process between the wind turbine’s wake and the main flow area,which accelerates the recovery rate of the wake area. |
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