Wind and Snow Impacts on Urban Space Planning:A Multiphase Numerical Simulation

The wind and snow environment outside the planned space plays a key role in the comfort and safety of the human habitat in severe cold regions. Traditional studies of the external environment of human settlements, however, frequently overlook the combined impacts of wind and snow environments. Furthermore, in urban meteorological studies, it is impossible to accurately assess the wind and snow environment in specific areas or locations. In this study, a refined Computational Fluid Dynamics(CFD) multiphase flow numerical method was used to simulate a planning space's wind and snow environment. The study classified the Snowstorm Weather Grade(SWG) by incorporating the Snowstorm Weather Index(SWI) to generate calculation results of the wind environment and snow environment. In particular, 150 measurement points in the planning space were chosen for analysis and evaluation of their wind and snow environments. The results demonstrated that the SWI index can effectively correlate to the wind and snow environment calculation results. In addition, the graph of SWI showed that 55% of the measurement points had a moderate wind and snow grade SWI, which exceeds the average grade for the entire region. The practical application shows that the wind and snow environment assessment indexes and technical methods developed in this paper can be successfully applied to wind and snow environment studies in other cold cities.

Numerical Simulation Analysis and Ecological Evaluation on Wind Environment of Dwelling Groups in Severe Cold Regions

The wind environment around residential building groups is increasingly concerned,while the dwelling groups as the elementary unit of planning design,its quality of surrounding wind environment will directly affect people's life. This study based on the climatic conditions of severe cold regions,selects four dwellings groups with different openings scale and position as the research objects,and then simulates and analyzes the wind speed distribution characteristics of each pattern. Meanwhile,it extracts the wind speed values of one hundred points of each pattern and applies the coefficient of uniformity method to the ecological evaluation. It has been found that grouping pattern of buildings has a dramatic effect on the resulting airflow behavior. Configurations that contain a T-shaped central space with small opened side can effectively prevent and contain airflow in the site offer. The interactive influence between layout of dwelling groups and wind environment are explored,so as to provide basis for the planning design of dwelling groups.

Numerical simulation of wind-driven circulation and pollutant transport in Taihu Lake based on a quadtree grid

In this study,a two-dimensional flow-pollutant coupled model was developed based on a quadtree grid.This model was established to allow the accurate simulation of wind-driven flow in a large-scale shallow lake with irregular natural boundaries when focusing on important smallscale localized flow features.The quadtree grid was created by domain decomposition.The governing equations were solved using the finite volume method,and the normal fluxes of mass,momentum,and pollutants across the interface between cells were computed by means of a Godunov-type Osher scheme.The model was employed to simulate wind-driven flow in a circular basin with non-uniform depth.The computed values were in agreement with analytical data.The results indicate that the quadtree grid has fine local resolution and high efficiency,and is convenient for local refinement.It is clear that the quadtree grid model is effective when applied to complex flow domains.Finally,the model was used to calculate the flow field and concentration field of Taihu Lake,demonstrating its ability to predict the flow and concentration fields in an actual water area with complex geometry.

CFD Investigation of Diffusion Law and Harmful Boundary of Buried Natural Gas Pipeline in the Mountainous Environment

The leakage gas from a buried natural gas pipelines has the great potential to cause economic losses and environmental pollution owing to the complexity of the mountainous environment.In this study,computational fluid dynamics(CFD)method was applied to investigate the diffusion law and hazard range of buried natural gas pipeline leakage in mountainous environment.Based on cloud chart,concentration at the monitoring site and hazard range of lower explosion limit(LEL)and upper explosion limit(UEL),the influences of leakage hole direction and shape,soil property,burial depth,obstacle type on the diffusion law and hazard range are analyzed.Results show that the leakage gas is not radially diffused until it reaches the ground,and the velocity of gas diffusion to the ground and the hazard range decrease as the angle between the leaking direction and the buoyancy direction increases.Triangular and square leak holes have a faster diffusion rate and a wider hazard range than circular.The diffusion rate of leakage gas in soil rises as soil granularity and porosity increase.The time of leakage gas diffusion to the ground increases significantly with the increase of burial depth,and the hazard range reduces as burial depth increases.Boulder-type obstacles will alter the diffusion path of the leakage gas and accelerate the expansion of the hazard distance,while trench-type obstacles will cause the natural gas to accumulate in the trench and form a high concentration region slowing the expansion of the surface gas concentration.

Numerical simulation of wind flow fields around buildings using the lattice Boltzmann method

This paper presents the simulation results of the wind environment around a single high-rise building and that around two tall buildings in tandem arrangement by using the lattice Boltzmann method with an aim to understand the ventilation issues around high-rise buildings in an urban environment.We analyzed the velocity distribution around the buildings and performed numericl simulations to reveal the formation and evolution law of the complex vortex system around the high-rise buildings.Numerical simulation results manifest a periodicity phenamenon in the process of the vortex evolution.For the case of two high-rise buildings,wind velocity in the space between the two buildings is very small,which is nearly a silent regime.Wind velocity above the front building is relatively larger and the maximum wind velocity is approximately 2.5 times the incoming wind velocity.The numerical results can be used in layout planning of high-rise residential buildings to create better environment for ventilation purpose in an urban area.

Ventilation control of tunnel drilling dust based on numerical simulation

In order to control the dust pollution produced by air leg rock drill in the trolley area during the excavation of long-distance single ended tunnel,the full-scale physical model of working face was established by using FLUENT software,and the numerical simulation analysis of tunnel drilling ventilation and dust removal parameters was carried out.The results show that it is difficult to control the dust pollution of the face by conventional ventilation,and the drilling dust is distributed in the range of 10 m from the face;after the introduction of the long pressure and short suction ventilation scheme,when the ratio of compressed air volume to exhaust air volume is 0.72,the height of the pressure fan is 2.5 m,the distance between the pressure fan and the palm face is 20 m,and the exhaust fan is 12 m away from the palm,the dust concentration control efficiency of the working face is increased by about 60%.Therefore,in the similar long-distance single head tunnel construction,it is appropriate to adopt the dust removal method of long-distance short suction and exhaust fan to ensure the working environment.

Numerical Simulation of Groundwater Pollution Problems Based on Convection Diffusion Equation

The analytical solution of the convection diffusion equation is considered by two-dimensional Fourier transform and the inverse Fourier transform. To get the numerical solution, the Crank-Nicolson finite difference method is constructed, which is second-order accurate in time and space. Numerical simulation shows excellent agreement with the analytical solution. The dynamic visualization of the simulating results is realized on ArcGIS platform. This work provides a quick and intuitive decision-making basis for water resources protection, especially in dealing with water pollution emergencies.

不同建筑环境下平均风速剖面的数值模拟

基于计算流体力学(CFD)方法对具有不同建筑环境参数的城市上空的风场进行系统性的数值模拟,并对平均风速剖面指数的变化规律进行讨论。研究结果表明,建筑平均高度对平均风速剖面指数的影响较大,建筑密度对平均风速剖面指数的影响较小。文中还给出了以建筑平均高度和建筑密度为自变量的平均风速剖面指数经验公式。

送风方式对高速列车通风和呼吸污染物扩散特性的影响

高速列车交通网络发达且载客量大,但车厢环境封闭易造成污染物的堆积,为提高乘车舒适性和安全性,基于计算流体动力学理论(CFD),建立满载工况的全尺寸车厢通风计算模型.针对排风口位于两侧车窗上端的排风方式,采用速度不均匀系数、温度不均匀系数、能量利用系数和通风效率作为列车通风系统的评价指标,对比研究6种送风方式对车厢内流场特性和呼吸污染物扩散特性的影响,包括多孔顶板送风、下部送风、多孔顶板送风+下部送风、局部多孔顶板送风、侧顶送风、局部多孔顶板送风+侧顶送风.研究结果表明:通过调整风口之间的流量分配比例可以使送风气流均匀地流向客室两侧,改善车内温度均匀性;采用下部送风时,有助于提高通风系统的能量利用系数和通风效率,分别高达1.38和1.21,但会恶化车内乘坐舒适性;通过研究乘客之间呼吸污染物的相互影响情况发现,第C列乘客的呼吸污染物容易向第B列乘客的呼吸区域进行扩散,加剧乘客之间的交叉感染;通过减小多孔顶板的送风口尺寸,采用局部多孔顶板送风可以有效缓解该现象,使污染物的体积浓度下降至0.0019.

前缘圆柱对风力机翼型气动性能及冲蚀磨损影响研究

为研究风沙环境下流动控制方式对于NACA 0012翼型气动性能和冲蚀磨损的影响,通过在风力机翼型前缘布置微小圆柱来控制气流流动,采用离散项模型和SST k-ω湍流模型对控制翼型进行数值计算。结果表明:攻角较小时,微小圆柱处于X=0.04、Y=-0.03位置时控制效果最佳,可抑制流动分离,相比原翼型升阻比提高149.72%;微小圆柱处于X=0.02、Y=-0.02位置时翼型冲蚀磨损的减小量最大,相比原翼型减小97.66%;微小圆柱处于最优区域时翼型升阻比提高的同时冲蚀磨损量也会减小。

台风条件下航站楼风环境数值模拟研究

以杭州萧山机场T4航站楼为对象,采用Realizable k-ε湍流模型进行了周边风环境数值模拟。首先通过与刚性模型测压风洞试验结果的对比,验证了该数值模拟方法及参数的有效性;然后,研究了不同风向角下行人高度(2 m)处加速比的变化规律,以及台风登陆情况下距离地面10 m高度处的风速分布情况。结果表明:航站楼两侧的角点位置处和西侧建筑群迎风面道路间易受角隅效应和峡谷效应的影响,存在明显的风加速现象,在台风登陆条件下,航站楼周边大部分区域风速达到六级(强风)以上,而陆侧交通中心区域由于四周建筑的遮挡,所受影响相对较小。

建筑底层架空对行人高度处风环境及污染物扩散影响的数值模拟

在规则建筑群内,考虑建筑底层的架空设计,利用realizable k-ε紊流模型数值模拟了6种工况下的风场和污染物浓度场,并采用时均风速比M_(VR)、风速面积占比A_(RSi)和无量纲浓度K等指标对行人高度处的风环境和污染物浓度进行了评价。建筑底层的架空设计能有效增加行人高度处的M_(VR),上游建筑的架空对M_(VR)的增加效果更显著。架空设计能减小低风速A_(RSi),增加中风速和中高风速A_(RSi),当建筑群中有2列及以上的建筑采用架空设计时,A_(RSi)的改善效果更好。当污染源位于建筑群上游地面时,架空设计对行人高度处的K分布影响不大,架空导致的回流使得污染物难以扩散至建筑群内,还会因其架空导致紧邻污染源的建筑迎风面行人高度处的K显著变小。

风环境性能导向的围合式教学楼庭院架空空间优化设计研究——以中国石油大学古镇口校区为例

该文通过选取30例国内21世纪建成高校围合式教学楼进行调研,归纳总结出9种围合式教学楼形态类型,以出现频次较高的B1型围合式教学楼——中国石油大学古镇口校区围合式教学楼为研究对象,以架空空间形体尺寸为变量,运用性能模拟软件建立模型并对庭院风环境进行仿真模拟,探究架空空间形体尺寸与庭院风环境的关联关系,计算边界条件下的较优因素组合。结果表明,架空长度对庭院风环境影响最大,且在冬夏季庭院风环境优化方面取值差异较大;架空宽度对风速离散度影响较大;架空高度与庭院风环境未呈现出线性的相关性。研究方法及结论可对青岛地区围合式建筑架空空间设计阶段庭院风环境优化提供参考。

一种计算机模拟的针阔林木抗风性能分析

自然界中的强风常常对树木造成不可逆破坏,分析强风穿过时树林内部的气流情况有利于评估树木的抗风性,更好地理解如何减轻风的影响。以阔叶树和针叶树为原型,提取了二者叶团簇和枝干构造的特点,建立两种结构不同的树木模型,组合成树林模型,在3个不同叶面积密度下进行风力作用下的仿真模拟实验。分别使用改进的k-ε双方程模型和k-ω双方程模型以设置风环境,并且用龙格-库塔法分析求解湍流模型。k-ε双方程模型下,当叶面积密度分别为1,5和10 m~2/m~3时,阔叶林背风侧20 m处的最低风速与入口风速相比下降了49.60%,67.23%和80.40%,针叶林分别为55.13%,68.90%和78.29%。k-ω双方程模型展示了阔叶树林内部风场的复杂性。结果表明,叶面积密度与树林挡风能力之间是非线性关系,树林的挡风能力随叶面积密度的上升而增强,增强到一定程度后上升幅度减缓。不同的树木结构会导致风场的变化,影响同等强度风荷载下的受损概率和挡风能力。叶面积密度高、树冠体积大的树木更容易在强风中受到损害。

基于对流扩散方程的水质预测模型研究

为了实现河流水质的细粒度监测,以对流扩散方程为基础,构建细小水段的水质关系模型,在空间维度上对流域水质进行预测。首先,求解一维对流扩散方程的显示差分解、隐式差分解和解析解(也叫精确解),构建出以一定的时间步长和空间步长为单位的细小水段水质关系模型,并对这些方法的精度进行验证。然后,依据木兰溪的实际水文情况,以某段为例,按照构建的对流扩散水质预测模型,求解该河段中某时刻各个节点的污染物浓度,实现该河段水质的细粒度预测,通过该应用验证隐式差分法具有较高的精度,使用隐式差分法进行空间维度预测具有一定可行性。

灌木篱墙对高架桥街道峡谷内CO扩散的影响

为探究灌木篱墙布局对高架桥街道峡谷内部流场及污染物扩散的影响,将灌木篱墙假设为多孔介质,采用标准k-ε模型结合组分运输方程对布置中央灌木篱墙和两侧灌木篱墙的高架桥街谷的底部和桥面道路机动车排放的CO扩散过程进行模拟,并与风洞试验结果比较。结果表明:数值模拟方法可靠,且与标准街谷不同,高架街谷中的灌木篱墙不仅不会阻碍流场运动,还能加强底部受阻风场与上部风场的对流,有利于底部道路排放污染物的扩散,能够有效降低街谷的整体污染物浓度,改善污染物在背风侧、桥体上方和底部集聚的问题。两侧均设置篱墙时风场的上下对流更强,背风面壁面处CO质量分数降低60%,增设灌木篱墙可作为改善其内部空气污染程度的有效措施。

基于CFD数值模拟的古建筑群风场特性研究——以北京故宫建筑群为例

为研究我国古建筑群风场特性评估方法,基于计算流体动力学方法(Computational Fluids Dynamics,CFD),以北京故宫建筑群为例,通过对不同风向角工况下的故宫建筑群进行CFD数值模拟,获得全域流场信息,包括故宫中轴线主要建筑的表面风压分布情况、以及故宫建筑群环境风速分布情况.研究揭示了故宫建筑群内不同风向角下主要建筑表面的风压分布规律、中轴线建筑的不利风向角,并基于风环境评估理论对故宫建筑群内的行人风环境舒适性和安全性进行评估.研究结果表明:风压分布大致呈东西和南北对称分布形态;迎风面受较大正风压,侧风和背风面受较大负风压,负风压主要集中在靠近屋脊和墙面转角等气流分离区;主要建筑表面的正风压系数最值达1.0,负风压系数最值达2.2;六座大殿所受竖直方向的升力系数极值接近8,是水平方向的2倍;在水平和竖直方向上风压合力在斜风向下较大,其中在120°时的三向风压合力均达到极值;环境最大风速比在3~6之间,斜风向的最大风速比较大;垂直风向下,风速放大效应较弱,其中正南和正北风放大效应最弱,北京地区的主导风向是故宫建筑群的最优风向.研究成果可以为故宫建筑群的结构抗风保护以及行人防风措施提供科学依据和指导.

湿热风缓地区传统聚落空间对风环境的影响效应

目的综合解析湿热风缓地区传统聚落空间对风环境的影响效应。方法基于田野调查,利用CFD软件对聚落整体和聚落建筑的风环境进行模拟分析;选取凤台村3栋典型三合院,分析不同长高比和宽高比对聚落空间风环境的影响。结果在聚落整体街巷结构与建筑密度的综合影响下,凤台村冬季的聚落空间风速总体呈东北高、西南低的分布特征,夏季的聚落空间风速呈由村口向东北方向的递增规律,聚落整体风环境良好;模拟分析得出聚落建筑吊脚干栏的最佳空间形制:宽高比为6,长高比为7.2。结论聚落空间风环境受到街巷结构与季节主导风、建筑形态与密度的综合影响,传统聚落空间形制体现了对区域风环境的高效适应,以及对局部微气候的有效利用,建议在进行聚落保护规划与地域建筑设计时应遵循此空间形制特征。

井下移动热源对深部巷道风流环境影响研究

为探究深部巷道内移动热源对巷道风流环境的影响,以新城金矿为工程背景,对深部某中段运输巷道进行风温风速监测,通过现场调研和理论公式计算新城金矿深部巷道燃油设备放热量,基于Fluent有限元软件,模拟不同风流情况下移动热源的动态响应,分析移动热源对深部巷道风流环境的影响。结果表明:监测段巷道平均风速为1.91 m/s,平均风温为33.38℃;热源在顺风移动时对前端和尾部风温均产生影响,风温随距离增加逐渐减小,在热源前端15 m处趋于稳定,稳定风温为33.75℃,并在热源尾部2 m范围内持续产生高温;热源逆风移动时仅对尾部风温产生影响,风温在热源尾部0~20 m逐渐变小,并在热源尾部20 m处趋于稳定,稳定风温为34.12℃;热源逆风移动时对风流的影响范围比顺风移动时大,逆风移动时风温比顺风移动时高0.37℃。

综掘面新型分风器粉尘运移规律仿真模拟研究

针对综掘面高浓度粉尘污染问题,提出了一种新型压风筒分风技术,构建了风流-粉尘两相耦合数学模型,探究了不同通风条件分风器对粉尘污染影响规律。结果表明:风流分风比越大,迎头粉尘控制效果越好,但过大分风比会导致迎头区域粉尘浓度过高;在压风筒分风比为8∶2的条件下,压抽比增大会减弱控尘效果,但当压抽比增加到1.0以上时,高浓度粉尘区随着压抽比的增大而减小;当压风量580 m^(3)/min、抽风量390 m^(3)/min且分风比8∶2时,可将粉尘抑制在迎头6 m范围内。通过大柳塔煤矿现场实测验证,粉尘浓度平均误差为10.71%。为综掘面粉尘治理提供了一种新策略。