Study On The Simulation Of Atmospheric Boundary Layer Wind Field Based On WRF And CFD

The research on wind characteristics in the atmospheric boundary layer is considered as the basic work in the field of wind engineering.This atmospheric boundary layer contains majority of buildings and structures concerned in civil engineering,in which the wind characteristics exhibit dramatically impact on the wind effect of buildings.Unfortunately,the wind field simulation of the atmospheric boundary layer is generally complicate,due to the irregular turbulent motion in the boundary layer and the changeable physical properties on the underlying surface of this layer.In addition,the wind field simulation in the boundary layer is essentially a multi-scale problem.The wind flow in the boundary layer covers an extremely wide scale,ranging from a few meters as small as the building bypass flow and the pedestrian level wind environment,to thousands of kilometers as massive as the typhoon motion and the kilometer-scale wind field.Based on the above difficulties,numerical simulation methods have been widely used in multi-scale wind field simulation,among which,the mesoscale WRF(Weather Research and Forecasting)model in meteorology and CFD(Computational Fluid Dynamics)method in engineering are dominated methods to study the mesoscale and microscale flow in the atmosphere,respectively.Therefore,this work will introduce the numerical simulation of the wind field characteristics of the atmospheric boundary layer in three aspects based on the WRF model and CFD technology,as shown in the following:(1)Study on mesoscale typhoon simulation.Firstly,the super typhoon "Mangkhut"(2018)is simulated with high precision based on the mesoscale WRF model,and FDDA(Fourdimensional Data Assimilation)technology was successfully loaded into the WRF model,reproducing the mesoscale evolution process of typhoon.Subsequently,the wind field characteristics derived from the simulation were compared with the observation data of Shenzhen meteorological tower in detail to verify the assimilation effect and simulation accuracy of FDDA method.The results show that the mesoscale wind field characteristics,such as typhoon path,typhoon intensity and averaged wind speed simulated by Analysis Nudging method(AN),are consistent with the measured data in a statistical sense.This means that the refined WRF simulation can realize the accurate prediction of typhoon wind field.It is also worth to mention that the change rule of the averaged wind profile above the gradient wind height is not invariable,nor is it applicable to the exponential rate model specified in the code.(2)Study on wind field simulation of complex terrain in a microscale and mesoscale coupled model.In this paper,the mountainous area around the Shenzhen meteorological tower is selected as the simulation area.Based on the coupled model of WRF and CFD,the local flow field of the complex terrain is simulated,while the results are compared with the observed data.The results show that,the simulated data employing the coupled model are more consistent with the measured one in comparison to the single WRF method,clarifying that the accuracy of numerical simulation is further improved by the WRF-CFD coupled method.In this case,the mesoscale WRF model can provide relatively more accurate inlet boundary conditions for microscale numerical wind tunnels,while the CFD model can realize scale-down wind field simulation in boundary layer through more refined grid discretization.In all,the combination of the two methods can be an effective way to improve the accuracy of wind effect simulation results of super high-rise buildings;(3)Study on wind load and pedestrian wind environment of high-rise buildings.In this paper,a serial of wind tunnel tests of an idea built-up area were carried on to investigate the influence of different building height and wind direction on building surface wind load and pedestrian wind environment around based on AIJ(Architectural Institute of Japan)model.The corresponding CFD simulations by means of both RANS(Reynolds average Navier Stokes)and LES(Large Eddy Simulation)methods were simultaneously made to partly answer above questions,and we compared the accuracy of numerical simulation results of RANS and LES.The wind tunnel test results show that,the asymmetric arrangement can increase the negative pressure and the positive pressure of the windward side at the bottom corner of the crosswind side of the high-rise buildings compared with the symmetrical arrangement of the surrounding low buildings.The maximum wind speed ratio at the pedestrian height around the high-rise buildings is directly proportional to the building height(within the range of 0-225m).Besides,the oblique axial wind Angle of attack tends to have the most adverse effect on the pedestrian height of the building,and the maximum acceleration zone usually exists on the leeward side of the building near the narrow lane.The results of numerical simulation show that the distribution law of simulated wind speed ratio is basically consistent with the overall law of wind tunnel test results,but there are still some errors between the simulated wind speed and the wind tunnel test results near the central building.Compared with the results of RANS and LES methods,it can be seen that the results of LES are closer to those of the wind tunnel test.