共查询到19条相似文献，搜索用时 640 毫秒
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从湍流经典理论到大气湍流非平衡态热力学理论 总被引：2，自引：0，他引：2
湍流是日常生活中一种普遍的自然现象,也是经典物理学仍未完全解决的难题。湍流更是大气运动的最基本特征。本文系统地回顾了大气湍流经典理论发展简史,进一步详细介绍了大气湍流非平衡态热力学理论。大气湍流非平衡态热力学理论在熵平衡方程中引入动力过程,进而统一推导出大气湍流输送的Fourier定律、Flick定律和Newton定律,证明了Dufour效应、Soret效应、可逆动力过程与热力不可逆湍流输送过程之间的交叉耦合效应,以及湍流强度定理。这些定律和定理中得到了观测的事实验证,同时它们的唯象系数也由观测资料所确定。湍流强度定理揭示,湍流发展的宏观原因是速度和温度的剪切效应,Reynolds湍流和Rayleigh-Bénard湍流共存于大气湍流中。热力过程和动力过程间耦合效应现象的发现突破了传统湍流输送理论,即Fourier定律、Flick定律和Newton定律的观点——一个宏观量的输送通量等价于这个宏观量的梯度湍流输送通量。热力和动力过程间的耦合原理认为,一个宏观量的输送通量包括这个量的梯度湍流输送通量和速度耦合输送通量两部分。因此,能量和物质的垂直输送通量除了相应物理量梯度造成的湍流输送外,还应包括垂直速度耦合效应,即辐散或辐合运动造成的耦合效应。在一个很宽的尺度范围内,地表面的空间特征是非均匀的。下垫面非均匀性造成的对流运动将引起大气的辐散或辐合运动。这可能是导致地表能量收支不平衡的重要原因之一。垂直速度对垂直湍流输送的交叉耦合效应为非均匀下垫面大气边界层理论的发展,并为克服地表能量收支不平衡问题及非均匀下垫面大气边界层参数化遇到的困难提供了可能的线索。 相似文献
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湍流的分子动力学理论 总被引：3，自引：0，他引：3
湍流是自然界中极为普遍的一种流体运动形态。研究湍流运动发生发展的规律,在气象学、海洋学、空间物理、流体力学、等离子体物理以及不少工程技术等领域中,不仅具有重要的实用价值,而且是一个极有意义的理论问题,也一直引起各方面的密切注视。湍流理论的系统研究已有五十多年的历史,其主要成果大多建立于三十年代和四十年代初期。以后一个时期内,由于问题的复杂和困难,进展并不显著。近几年来,国内外对湍流 相似文献
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晴空湍流(Clear Air Turbnlence,以下简称CAT)是指出现在9千米以上高空、且与对流云无关的湍流。它排除了与对流性不稳定边界层及深厚对流有关的湍流,却并未排除非对流性云(多指卷云)中存在的湍流。因此,有人认为采用“急流湍流”或“高空湍流”,的术语似更合适。 相似文献
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根据流体力学的基本原理，建立了能量单方程植冠层湍流模式。并用小麦和玉米两种作物的实例资料对模式进行了验证。 相似文献
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《高原气象》2021,40(2):374-383
利用小兴安岭南麓五营地区涡动相关系统的观测资料,分析不同大气稳定度条件的湍流速度谱、温度谱、湿度谱、协谱及局地各向同性特征。结果表明:三维速度(u、v、w)谱和垂直速度(w)与水平纵向速度(u)、温度(θ)的协谱(uw、θw)的谱峰均随稳定度的增加而向高频端移动。湍流速度(u、v、w)谱、温度(θ)谱和湿度(q)谱在惯性副区均满足-2/3定律。uw协谱、θw协谱和垂直速度(w)与湿度(q)的协谱(qw)在惯性副区并不完全遵循-4/3定律,尤其是uw协谱的拟合斜率更接近-1。水平方向湍流谱峰波长范围为130～1820 m,垂直范围为49～113 m。温度谱谱峰波长范围为149～260 m,湿度谱谱峰波长范围为198～455 m。uw协谱谱峰波长范围为228～455 m,θw协谱谱峰波长范围为172～260 m,qw协谱谱峰波长范围为172～346 m。v谱在惯性副区基本满足局地各向同性,w谱在惯性副区不满足局地各向同性,可能与森林下垫面对垂直方向湍流大涡的破碎作用有关。 相似文献
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利用Burger's和巢纪平提出的湍流发生模型计算了不同R_e数和R_i数情况下系统的状态,可能的形态有:无扰动的基本场、重力内波、湍流。找到了这三种状态相互转换的临界R_e和R_i数值。指出R_i<1/4是出现湍流状态的必要条件。在R_i>1/4时,R_e=2π~2处是发生Hopf分岔出现重力内波(周期解)的条件。波和湍流的能量来自基本速度场和基本温度场,一旦波和湍流形成后又影响基本场.若初始的R_i在1/4附近(稍大于1/4),重力内波形成后最终可能使R_i数反小于1/4,进入湍流状态,这就是湍流和内波在大气中间歇发生的原因。所计算出的相轨线和Liapunov特征指数验证了各种状态的确实性。 相似文献
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Turbulent kinetic energy budgets from a large-eddy simulation of airflow above and within a forest canopy 总被引：3，自引：2，他引：3
The output of a large-eddy simulation was used to study the terms ofthe turbulent kinetic energy (TKE) budget for the air layers above andwithin a forest. The computation created a three-dimensional,time-dependent simulation of the airflow, in which the lowest third ofthe domain was occupied by drag elements and heat sources to representthe forest. Shear production was a principal source of TKE in theupper canopy, diminishing gradually above tree-top height and moresharply with depth in the canopy. The transfer of energy to subgridscales (dissipation) was the main sink in the upper part of the domainbut diminished rapidly with depth in the canopy. Removal ofresolved-scale TKE due to canopy drag was extremely important,occurring primarily in the upper half of the forest where the foliagedensity was large. Turbulent transport showed a loss at the canopytop and a gain within the canopy. These general features have beenfound elsewhere but uncertainty remains concerning the effects ofpressure transport. In the present work, pressure was calculateddirectly, allowing us to compute the pressure diffusion term. Wellabove the canopy, pressure transport was smaller than, and opposite insign to, the turbulent transport term. Near the canopy top andbelow, pressure transport acted in concert with turbulent transport toexport TKE from the region immediately above and within the uppercrown, and to provide turbulent energy for the lower parts of theforest. In combination, the transport terms accounted for over half ofthe TKE loss near the canopy top, and in the lowest two-thirds of thecanopy the transport terms were the dominant source terms in thebudget. Moreover, the pressure transport was the largest source ofturbulent kinetic energy in the lowest levels of the canopy, beingparticularly strong under convective conditions. These resultsindicate that pressure transport is important in the plant canopyturbulent kinetic energy budget, especially in the lowest portion ofthe stand, where it acts as the major driving force for turbulentmotions. 相似文献
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The influence of an idealized moving wavy surface on the overlying airflow is investigated using direct numerical simulations (DNS). In the present simulations, the bulk Reynolds number is Re = 8000 (; where U0 is the forcing velocity of the flow, h the height of the domain and v the kinematic viscosity) and the phase speed of the imposed waves relative to the friction velocity, i.e., the wave age varies from very slow to fast waves. The wave signal is clearly present in the airflow up to at least 0.15λ (where λ is the wave length) and is present up to higher levels for faster waves. In the kinetic energy budgets, pressure transport is mainly of importance for slow waves. For fast waves, viscous transport and turbulent transport dominate near the surface. Kinetic energy budgets for the wave and turbulent perturbations show a non-negligible transport of turbulent kinetic energy directed from turbulence to the wave perturbation in the airflow. The wave-turbulent energy transport depends on the size, tilt, and phase of the wave-induced part of the turbulent Reynolds stresses.According to the DNS data, slow waves are more efficient in generating isotropic turbulence than fast waves.Despite the differences in wave-shape as well as in Reynolds number between the idealized direct numerical simulations and the atmosphere, there are intriguing similarities in the turbulence structure. Important information about the turbulence above waves in the atmosphere can be obtained from DNS—the data must, however, be interpreted with care. 相似文献
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利用美国科罗拉多州立大学和MRC/ASTER发展的中尺度数值模式RAMS, 采用三重嵌套的方法, 模拟研究了兰州山谷地区局地环流特征。结果表明： （1）兰州市近地面流场以偏东风为主, 在城市东西部之间的狭窄地带, 风速相对较大些, 在东西部山谷城市中心区域有大片的静风区; 冬季兰州市山谷夜间是辐合流场, 白天是辐散流场。受城市热岛环流的影响, 白天热岛环流抑制谷风环流, 夜间增大山风环流, 夜间的山风风速大于白天的谷风风速。（2）白天, 兰州市区山顶和山谷之间上空气柱以下沉气流为主, 这主要是由于地形作用使得白天盛行谷风环流和山峰加热作用的共同影响。夜间, 兰州市区山顶和山谷之间上空以上升气流为主, 这主要是由于地形作用使得市区和山谷在夜间盛行山风环流, 但是冬天夜间兰州市区和山谷上空有较厚的逆温层存在, 抑制了气流的上升运动。（3）在午后13：00左右, 兰州市区山谷从近地面到400 m高度, 辐散场在逐渐减弱, 在510 m左右的高度转变为辐合场; 皋兰山顶上空从近地面到400 m高度, 辐合场在逐渐减弱, 在510 m左右的高度转变为辐散场。在凌晨01：00左右, 兰州市区山谷从近地面到400 m高度, 辐合场在逐渐增强, 到400 m高度达到最强, 从400 m到510 m高度又逐渐减弱; 皋兰山顶上空从近地面到220 m左右的高度, 辐散场在逐渐减弱, 在400 m左右的高度辐散场转变为辐合场, 从400 m到510 m左右的高度, 皋兰山顶的辐合场逐渐增强。 相似文献
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Nikki Vercauteren Elie Bou-Zeid Marc B. Parlange Ulrich Lemmin Hendrik Huwald John Selker Charles Meneveau 《Boundary-Layer Meteorology》2008,128(2):205-228
We examine the dynamics of turbulence subgrid (or sub-filter) scales over a lake surface and the implications for large-eddy
simulations (LES) of the atmospheric boundary layer. The analysis is based on measurements obtained during the Lake-Atmosphere
Turbulent EXchange (LATEX) field campaign (August–October, 2006) over Lake Geneva, Switzerland. Wind velocity, temperature
and humidity profiles were measured at 20 Hz using a vertical array of four sonic anemometers and open-path gas analyzers.
The results indicate that the observed subgrid-scale statistics are very similar to those observed over land surfaces, suggesting
that the effect of the lake waves on surface-layer turbulence during LATEX is small. The measurements allowed, for the first
time, the study of subgrid-scale turbulent transport of water vapour, which is found to be well correlated with the transport
of heat, suggesting that the subgrid-scale modelling of the two scalars may be coupled to save computational resources during
LES. 相似文献
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垂直湍流输送对大洋的重力位能和混合过程的影响 总被引：1，自引：0，他引：1
利用WOA09（World Ocean Atlas 2009）全球大洋温盐客观分析数据,计算了不同湍流垂直混合系数下全球大洋重力位能的变化,并分析了混合系数、浮力频率和重力位能变化之间的关系。在此基础上,进一步探讨了湍流混合造成的能量转换对湍流参数化的影响。结果表明,大洋中的垂直湍流运动不仅仅是动能能汇,而且是一个重要的外部能量转化为重力位能的途径。垂直湍流增加的重力位能在混合系数取0.1 cm2 s-1 时为0.08 TW,参考前人研究结果,外部能量输入甚至可引起等效于全球平均12 cm2 s-1 的垂直混合系数。一般而言,层结越稳定、混合系数越大,垂直湍流对重力位能的影响也越大。考虑湍流动能可转化为重力位能后,参数化方案可以得到和实际观测更接近的湍流动能耗散率和混合系数。 相似文献
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近地层湍流通量计算对于中尺度数值模式有重要意义, 湍流通量的参数化是当前大气边界层研究的重要课题之一。选择青藏高原东缘大理观象台边界层通量观测系统, 离线测试了WRF区域模式中的两种常用的近地层参数化方案(MM5相似理论非迭代方案A和ETA 相似理论迭代方案B), 并将参数化方案计算结果与边界层铁塔涡动相关法的观测值进行对比分析。在大理观象台观测场不同植被随季节交替的状况下, 根据边界层铁塔4层高度风速拟合, 发现近地层空气动力学粗糙度随季节变化特征明显。将拟合的空气动力学粗糙度输入模式参数化方案进行通量计算。结果表明:稳定度是影响近地层参数化方案精度的重要因素, 在不稳定条件下方案B低估了动量通量, 方案A优于方案B, 而在稳定条件下方案A低估了动量通量, 方案B优于方案A, 两种方案总体来看误差不大。对于大理边界层通量观测场地农田植被交替的环境条件, 不同季节下垫面植被类型的差异, 以及植被的稀疏对近地层参数化方案湍流通量计算结果的精度有显著影响。方案B考虑了空气动力学粗糙度z0和热量粗糙度z0h的差异, 不稳定条件下感热通量计算结果在裸土或稀少植被条件下明显优于方案A。针对方案B不稳定条件下感热通量计算结果在裸土下垫面仍出现高估的现象, 在使用了(Zeng, et al, 1998)提出的对于使用辐射地表温度在裸土下垫面时的订正方法后, 计算结果也有明显改善。 相似文献
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Local Imbalance of Turbulent Kinetic Energy in the Surface Layer 总被引：1，自引：1，他引：0
We utilize experimental data collected in 2002 over an open field in Hanford, Washington, USA, to investigate the turbulent
kinetic energy (TKE) budget in the atmospheric surface layer. The von Kármán constant was determined from the near-neutral
wind profiles to be 0.36 ± 0.02 rather than the classical value of 0.4. The TKE budget was normalized and all terms were parameterized
as functions of a stability parameter z/L, where z is the distance from the ground and L is the Obukhov length. The shear production followed the Businger–Dyer relation for −2 < z/L < 1. Contrary to the traditional Monin–Obukhov similarity theory (MOST), the shear, buoyancy and dissipation terms were found
to be imbalanced due to a non-zero vertical transport over all stabilities. Motivated by this local imbalance, modified parameterizations
of the dissipation and the turbulent transport were attempted and generated good agreement with the experimental data. Assuming
stationarity and horizontal homogeneity, the pressure transport was estimated from the residual of the TKE budget. 相似文献
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城市下垫面对河谷城市兰州冬季热岛效应及边界层结构的影响 总被引：5，自引：2，他引：3
利用中尺度数值模式WRF耦合单层城市冠层模块UCM,引入2005年MODIS土地利用类型资料,在对2005年1月25—28日兰州市热岛现象进行高分辨率数值模拟的基础上,设计了去除城市下垫面敏感性试验,探讨了城市下垫面对城市边界层的影响程度。结果表明,城市下垫面能使近地层大气温度升高而风速减小,并且,在夜间表现更明显。由城市热岛强度日变化分析可知,城市下垫面对兰州市热岛强度的贡献率为44%。夜间,城市上空200 m以下的近地层大气保持了白天的混合层特征,热岛环流的上升运动促进了山风环流,使得上升气流到达地面以上600 m左右;白天,由于山峰加热效应,城市上空400—600 m存在一个脱地逆温层,城市热岛环流使得11—15时（北京时）市区近地层出现弱上升气流,抑制了谷风环流的形成及发展。城市下垫面的低反照率特性和建筑物的多次反射作用导致城市下垫面的净辐射通量大于非城市下垫面;城市下垫面由于建筑材料的不透水性,导致潜热通量远小于感热通量,而储热项所占比重明显增大。 相似文献