油污染全场模拟的湍浮力流动k-ε模型

以通用的k-ε湍流模型为基础,针对油—水两相流动体系的特点,提出了油污染全场模拟的湍浮力流动k-ε模型.模型不仅在控制方程中计及了密度变化,而且在控制方程中加进了浮力项,并对湍流Schmidt数也作了浮力修正.从而计及了浮力对紊动的影响.结果表明,模型的模拟效果非常满意.     

水环境两相分层流数值模拟

以研究水环境两相分层流精细预报模型为目标,广泛地涉及了两相湍流精细模拟的理论和方法。用Eulerian坐标系中多流体模型统一描述两相各自的运动,并分别对两相本分的湍流输运观作以及地相间互作规律进计模拟,建立了水环境两相分层流的双流体模型对包含有浮力和密度分层的两相湍流进行了数值模拟,计算结正确地反映了分层及紊动特征,与实测结果吻合较好     

深度平均的应力-通量代数全场模型及其验证

提出了深度平均的应力—通量代数全场模型，用来模拟热水侧向排入大水体的各向异性的输移扩散规律。应用有限体积法对控制方程进行离散，利用ＳＩＭＰＬＥ法进行数值模拟。通过该模式的模拟计算给出了速度场、温度场的分布。所得的回流区形状及温度场分布与深度平均的ｋ－ε模型及实验资料对比，本文的计算结果与实测值符合得较好     

珠江口伶仃洋及磨刀门盐淡水混合特征及机制分析

基于2016年1月3日至18日的珠江口盐度分层观测资料,对比分析伶仃洋与磨刀门盐淡水混合特征及其机制,结果表明:（1）伶仃洋及磨刀门水域口门处盐度分层最明显,小潮阶段分层特征最显著;（2）磨刀门分层较伶仃洋更为显著,主要原因在于上游流量的差异;（3）大潮转小潮过程中,伶仃洋上游盐度虽向口门下落,但下落速度较慢,分层逐渐明显,而磨刀门水道中盐淡水却混合充分,这是由于盐度在河道中剧烈震荡并快速退出河口所致;（4）在伶仃洋及磨刀门口门附近,重力环流与潮汐剪切产生的抑制混合作用大于潮流紊动促进混合的作用,因此分层显著,河口上游水深较浅,潮流紊动作用较强,起到促进混合的作用。     

微囊藻属一日内垂向分布的数值模拟

将水质模型与微囊藻属浮力调节模型相结合,建立微囊藻属垂向浓度分布模型,该模型不仅保留了以往模型的优点且改进了以往模型的不足,如考虑了微囊藻群体的直径大小及微囊藻属的浮力调节能力.模型结果与荷兰的Vinkeveen湖的实际测量数据吻合良好.此外,模拟结果也表明:微囊藻属在垂向的分布受水体紊动程度影响显著.微囊藻群体的最大浓度并不在水体表面,而是在水下一定深度处.小尺寸群体微囊藻群体(20~50μm)在水深方向的分布比大尺寸群体(100~200μm)更加均匀.日落后,微囊藻属会因为密度减小上浮至水面,反之,白日里,微囊藻属密度增加向水底方向下沉,因此日出前水面的微囊藻属浓度高于日落前的水面浓度.     

环境地学

8表4参54(尹洋译)X143 200001974潮汐水域中污水侧向排放的数值模拟/梁书秀(大连理工大学海岸和近海工程国家重点实验室)…//海洋学报/中国海洋学会一2000,22(2)一113一119.环图P一38 基于N一S方程,采用深度平均的应力一通量代数全场模型,模拟流场及热水或污染物侧向排人大水体的各向异性的输移扩散规律。模型中采用深度平均的连续、动量、温度方程进行潮汐流动的数值模拟计算,潮流采用非对称潮流,模拟结果给出了一个周期内流场、污染物浓度场随时间的变化特征,所得的数值结果与他人的模型实验结果非常一致,而较其他结果更合理,说明本模型…     

紊流作用下泥沙释放磷的试验及数值模拟

为研究水体紊动对泥沙释放污染物的影响,引入近似均匀紊流模拟装置,开展不同强度紊动作用下泥沙运动释放磷动态过程及基本规律的试验,研究表明:紊动扩散作用对泥沙解吸释放磷有着十分重要的影响,紊动较弱时,泥沙尚未起动,床面泥沙颗粒吸附的磷元素解吸至孔隙水中,在垂向紊动扩散作用下输送至上覆水中,将使得上覆水中溶解态磷浓度增大;紊动作用较强时,泥沙逐渐悬扬至水体中,悬浮泥沙颗粒吸附的磷元素直接解吸至上覆水中,泥沙浓度越高,溶解态磷含量增长速率越大,达到平衡的时间越短.通过耦合紊流模型、水流泥沙数学模型、污染物对流扩散模型和Langmuir吸附动力学方程建立了紊动作用下泥沙释放磷的垂向一维数学模型,针对试验条件进行数值模拟,模拟结果与试验数据吻合较好,平均相对误差低于10%,可为模拟天然水体中泥沙悬浮释放磷的时空演化提供参考.     

紊流作用下泥沙释放磷的试验及数值模拟

为研究水体紊动对泥沙释放污染物的影响,引入近似均匀紊流模拟装置,开展不同强度紊动作用下泥沙运动释放磷动态过程及基本规律的试验,研究表明:紊动扩散作用对泥沙解吸释放磷有着十分重要的影响,紊动较弱时,泥沙尚未起动,床面泥沙颗粒吸附的磷元素解吸至孔隙水中,在垂向紊动扩散作用下输送至上覆水中,将使得上覆水中溶解态磷浓度增大;紊动作用较强时,泥沙逐渐悬扬至水体中,悬浮泥沙颗粒吸附的磷元素直接解吸至上覆水中,泥沙浓度越高,溶解态磷含量增长速率越大,达到平衡的时间越短.通过耦合紊流模型、水流泥沙数学模型、污染物对流扩散模型和Langmuir吸附动力学方程建立了紊动作用下泥沙释放磷的垂向一维数学模型,针对试验条件进行数值模拟,模拟结果与试验数据吻合较好,平均相对误差低于10%,可为模拟天然水体中泥沙悬浮释放磷的时空演化提供参考.     

环境地学

学/中科院生态环境研究中心一1999,20(3)一,l一4环图X一5X143 20(X) 00031水环境两相分层流数值模拟/沈永明…(大连理工大学海岸和近海工程国家重点实验室)//中国环境科学/中国环境科学学会一1999,19(3)一2巧一218_环信X一58 以研究水环境两相分层流精细预报模型为目标,广泛地涉及了两相湍流精细模拟的理论和方法,用Eulerian坐标系中多流体模型统一描述两相各自的运动,并分别对两相本身的湍流输运规律以及相间相互作用规律进行模拟。建立了水环境两相分层流的双流体模型。对包含有浮力和密度分层的两相湍流进行了数值模拟,计算结果正确地…     

异波折板流场模拟分析与结构优化

基于FLUENT技术,以连续方程、Navier-Stokes方程及k-epsilon湍流方程作为流动基本控制方程,对异波折板絮凝反应流场进行了数值模拟,并通过网格独立性检验,保证了模拟结果的真实性.以流场速度分布、紊动动能、有效能耗作为评价标准,根据数值模拟提出了不同絮凝段的最优折板单元组合.结果表明,夹角90°的短折...     

Numerical simulation of stratified turbulent two phase flow in aquatic environment

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Plume rise,entrainment and dispersion in turbulent winds

This paper describes a new analytical model which combines within one theoretical framework several aspects of the phenomena of plume rise, dispersion, thermal stratification and ambient turbulence. The model is based in part on knowledge gained from recent investigations of flow within free shear layers. The observations suggest a simple model for the turbulent mixing process, which accounts for the known entrainment of air into smoke plumes by plume-generated turbulence. More importantly, the model also predicts a path by which ambient turbulence causes reverse entrainment of plume material into the surrounding fluids. This gives rise to a new ‘extrainment’ term in each of the plume momentum and buoyancy equations.These equations are solved for a turbulent atmosphere of arbitrary thermal stability, and yield plume trajectories which gradually level off at final rise heights that depend on the degree of thermal stratification and on the scale and intensity of ambient turbulence. A link between plume rise and dispersion is identified by means of the concentration species equation, which is solved to show that the plume acts along its length as a distributed source of passively dispersing material.The new theory, specialized for an adiabatic atmosphere, plus the familiarx^2/3 law and a semi-empirical final rise theory from the literature, are all compared against full-scale data on plume rise in turbulent winds. The new theory significantly improves the accuracy of estimates of plume trajectory and final plume height. The price for this improved predictive ability is the need to evaluate the air temperature and its gradient at plume level, and the corresponding intensity and scale of turbulent air movement. This is no longer a technical obstacle since recently developed SODAR and RASS remote sensors have this capability.     

藻华高风险期微囊藻在洱海中的垂直分布特征及其影响因素

大量微囊藻浮力调节及其垂向迁移是形成蓝藻水华的重要机制之一.为研究微囊藻的垂直分布特征及影响因素,以洱海北部湖心为监测点位,采用野外采样室内分析的方法,于2016年9—12月对微囊藻生物量、伪空胞体积、粒径等指标进行了测定.结果表明:9—11月微囊藻生物量逐月增长并于11月达到峰值（1.77 mg/L）,在12月出现下降（月均值为0.34 mg/L）;9月、11月微囊藻伪空胞体积（18.0~22.6 μm3/cell）较高,10月、12月较低（10.2~17.3 μm3/cell）;9—11月微囊藻的垂向迁移速率（5.4~14.5 m/d）、漂浮百分率（57%~96%）及群体粒径（91~305 μm）逐渐增大,12月明显减小.微囊藻生物量、伪空胞体积及群体粒径的垂直分布规律均表现为表层最高,中层次之,底层最低.9—11月,微囊藻在洱海中出现垂直分层现象,伪空胞提供的浮力作用和藻群体粒径作用大于风力扰动作用,促使微囊藻在水柱中主动迁移并聚集在水面;而在12月,风力扰动对微囊藻垂直分布的影响远超过浮力及粒径的作用,微囊藻在水柱中趋于均匀分布.研究显示,藻华高风险期微囊藻在洱海呈弱分层分布,且浮力及群体粒径是影响其垂直分布的主要因子.      

A large-eddy simulation of a line source in a convective atmospheric boundary layer—II. Dynamics of a buoyant line source

We consider a large-eddy simulation of a buoyant line source in a convective boundary layer. The motion of the line source as a function of time is influenced by two contributions: internal buoyancy (plume rise) and ambient turbulence. The advantage of large-eddy modelling with respect to laboratory and atmospheric experiments is that the simulations allow us to distinguish between these two contributions. For the part due to internal buoyancy we formulate an integral model for plume rise. A new feature in this model is the fact that plume looping, which is characteristic for plume dispersion in a convective boundary layer, promotes entrainment and therefore reduces plume rise. The contribution by ambient turbulence to plume motion is modelled in terms of the standard deviation of vertical velocity fluctuations. The results of these models are consistent with our large-eddy simulations.     

屋顶形状对街道峡谷内污染物扩散的影响

采用Spalart-Allmaras湍流模型,通过求解二维连续性方程,Navier-Stokes方程及污染物输运方程,模拟了具有不同屋顶形状的街道峡谷的流场及交通污染物浓度场.计算结果与风洞试验结果总体趋势一致.由于屋顶形状的不同,峡谷内的流场会形成顺时针或逆时针方向的旋涡,从而影响建筑物迎风面与背风面污染物浓度分布.在各种屋顶形状的街道峡谷中,壁面污染物浓度的相对大小与其附近的速度分布有直接关系.通过对街道峡谷建筑屋顶高度处垂直方向污染物通量的计算和比较,说明了不同屋顶形状的街道峡谷平均流扩散和湍流扩散的强弱,污染物湍流扩散通量值有可能为正或为负;同时,峡谷内剩余污染物浓度的大小表明了屋顶形状对污染物扩散出街道峡谷难易的影响.      

A computational model for the rise and dispersion of wind-blown,buoyancy-driven plumes—I. Neutrally stratified atmosphere

A multi-dimensional computational model for the rise and dispersion of a wind-blown, buoyancy-driven plume in a calm, neutrally stratified atmosphere is presented. Lagrangian numerical techniques, based on the extension of the vortex method to variable density flows, are used to solve the governing equations. The plume rise trajectory and the dispersion of its material in the crosswind plane are predicted. It is found that the computed trajectory agrees well with the two-thirds power law of a buoyancy-dominated plume, modified to include the effect of the initial plume size. The effect of small-scale atmospheric turbulence, modeled in terms of eddy viscosity, on the plume trajectory is found to be negligible. For all values of buoyancy Reynolds number, the plume cross-section exhibits a kidney-shaped pattern, as observed in laboratory and field experiments. This pattern is due to the formation of two counter-rotating vortices which develop as baroclinically generated vorticity rolls up on both sides of the plume cross-section. Results show that the plume rise can be described in terms of three distinct stages: a short acceleration stage, a long double-vortex stage, and a breakup stage. The induced velocity field and engulfment are dominated by the two large vortices. The effect of a flat terrain on the plume trajectory and dispersion is found to be very small. The equivalent radii of plumes with different initial cross-sectional aspect ratios increase at almost the same rate. A large aspect-ratio plume rises slower initially and then catches up with smaller aspect-ratio plumes in the breakup stage. The Boussinesq approximation is found to be valid if the ratio of the density perturation to the reference density is less than 0.1.     

高速列车隧道会车流场的CFD分离涡数值模拟

目的研究高速列车隧道会车压力波及列车尾流特性。方法建立某型高速列车三节车模型,采用脱体涡方法数值模拟两列车以350km/h在隧道内等速会车的流场。数值模拟的空间离散化压力项、密度项及修正的湍流黏度项使用二阶迎风格式,动量项使用有界中心差分格式,时间离散采用预处理二阶精度差分格式,用壁面函数处理隧道壁,使用雷诺时均法作方法对比。计算列车车头、侧墙及尾车等部位的压力时间历程,然后使用傅里叶变换对尾车测点进行频谱分析,最后对尾流中不同位置的湍流强度进行分析。结果头车所受压力波动最为剧烈,中间车次之,尾车最小。列车侧墙同一垂向位置不同高度压力变化相差不大。列车尾涡主频在3.85Hz附近,其可能对列车横向振动有一定的影响。结论尾涡是两个不断向后发展的中等强度涡旋,在充分发展段,其湍流强度会有一个较为明显的抬升,之后逐渐减弱。会车侧涡流由于横向发展较为迅速,导致其强度较小且减弱速度较快。