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1.
An experimental investigation of the airflow structure in the near surface region over the wind-sheared air–water interface
is reported. The two-dimensional velocity fields in a plane perpendicular to the water surface were measured using particle
image velocimetry (PIV) technique over a wind speed range from 1.5 to 4.4 m s−1. The results show a reduction in the mean velocity magnitudes and the tangential stresses when gravity waves appear on the
surface. An enhanced vorticity layer was observed immediately above the water surface that extended to a height of approximately
2 cm. The vorticity was enhanced by an order of magnitude, and the energy dissipation rate was enhanced by a factor of 7 in
this layer at all wind speeds. The vertical profiles of Reynolds stress, energy production, and dissipation indicate the contribution
of surface waves in the enhanced transfer of momentum and energy between the two fluids. The results in this study show that
the flow dynamics in a layer immediately adjacent to the water surface whose thickness is of the order of the significant
wave height is significantly different from that at greater heights. Thus, it is concluded that the quantitative investigation
of the flow in the immediate vicinity of the interface is vital for an improved understanding of the heat, mass, and momentum
exchange between air and water. The present study demonstrates that PIV is an effective technique to accurately measure the
velocity fields in this region. 相似文献
2.
气流通过水域时的变性 总被引：1，自引：0，他引：1
利用量纲分析和数理方法推得了可用解析函数表示的气流通过水域时各气象要素在水上和下风岸陆地上变化的公式，并用１９８２年１，４，７，１０月在江苏兴化县大纵湖专门布点进行水域气候效应系统观测的资料对所得公式进行检验，同时根据理论结果和实际观测资料研讨气流通过水域时各气象要素变化的规律 相似文献
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4.
应用雷诺应力湍流模型,模拟了不同高度比的城市街道峡谷的气流场。结果表明:峡谷的对称性对其内部气流场有显著影响。前高后低型峡谷下部为逆时针旋涡,上部为顺时针旋涡,峡谷越深,流场发展的越充分;峡谷内部墙面存在明显的驻点。前低后高型峡谷只存在一个大的顺时针旋涡,随着峡谷的加深,内部气流速率有减小的趋势;峡谷达到一定深度后出现驻点。对称型峡谷内部形成了顺时针旋涡,强度不大;随着峡谷的加深,内部流场转为一顺一反2个旋涡的二元结构;仅当峡谷很深时才出现明显驻点。前低后高型峡谷的气流场形式更有利于污染物的迁移、扩散,在城市规划中应尽量结合主导风向设计这类建筑布局。 相似文献
5.
The process of aeolian flux in wild areas is usually unstable due to turbulent fluctuation of airflow. The physical parameters of wind and aeolian flux have strong pulsation characteristics and are even intermittent. Since the classical aeolian flux equations derived from steady sediment transport processes do not take into account the physical parameters such as soil particle properties and airflow turbulence characteristics, they cannot accurately predict the process of sediment transport driven by turbulent wind. Based on the analysis of the variables contained in the classical aeolian flux equations and their effects on the aeolian flux, the soil particle properties and the airflow turbulent fluctuation which influence unsteady sediment transport process, and the delayed response of the unsteady sediment transport process to airflow turbulent fluctuation, then the steady and unsteady sediment transports were defined. Strictly, there is no steady sediment transport process in nature, but the sediment transport process in a short period of time can be roughly considered to be a steady sediment transport process as the fluctuation of sediment transport is very little. Thus, the unsteady sediment transport process in a long-term series can be regarded as series of steady sediment transport processes on an "appropriate time scale" (Δt). The construction principles, variables in unsteady aeolian flux equation, and establishing unsteady aeolian flux equation of the way which is the method of determining each variable by controlling the conditional experiments were put forward. Finally, the foreseeable key issues in the process of establishing the unsteady aeolian flux equation were discussed. 相似文献
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A steady-state, spatial, large-scale, non-linear problemof the air massmotion along an undulating mountain ridge is consideredin the framework of bulktheory. The ridge is assumed to be so high that the airmass cannot top it, and, insteadof the actual ridge itself, a high vertical wall withsinuousities identical to those of theridge is considered. It is assumed that the air massis bounded above by an inversioninterface (idealized inversion layer) overlain by ageostrophic, polytropic, atmospherethat is thermally homogeneous along the horizontaland stably stratified with aconstant geostrophic wind blowing along the meandirection of the ridge. Theinversion strength (potential temperature deficit) isnot constant and considered as anadditional dependent variable. Because of the Earth'srotation effects, the air massflow to the left of the ridge and that to the rightof the ridge differ considerably intheir features. The fact that the characteristictransverse linear scale of the problem(the generalized Rossby radius of deformation) issmall compared with thelongitudinal scale permits making simplificationsthat result in a semi-geostrophicmodel of the boundary-layer type. Then the problemcan be reduced to an ordinarydifferential equation, which admits a closed-formsolution. Analysis of the solutionenables one to deduce some general features ofthe process under investigation suchas, for example, orographic front formation,a transition from sub-critical to super-criticalwind and others. 相似文献
8.
Tide-induced airflow is commonly seen in coastal lands and affects ground stability especially with a less permeable pavement on the ground surface. A tide-induced airflow model in a two-layered unsaturated zone consisting of a highly permeable layer underneath a less permeable layer was established by Li and Jiao [Li HL, JJ Jiao. One-dimensional airflow in unsaturated zone induced by periodic water table fluctuation. Water Resour Res 2005;41:W04007. doi:10.1029/2004WR003916] to describe the one-dimensional airflow with constant atmospheric pressure at the ground surface. In this study, we expand the Li and Jiao model by considering the realistic atmospheric pressure fluctuations and the initial condition. A new transient solution to the airflow model is developed for an initial boundary value problem (IBVP). The transient solution can be used not only to calculate the subsurface air pressure at a future time with a known initial condition, but also to evaluate the asymptotic air pressure variations when time becomes long. The amplitude ratio and phase lag of the subsurface air pressure relative to the tide-induced hydraulic head variations inside the unconfined aquifer below the unsaturated zone are investigated. The results reveal that effect on the subsurface pressure due to changes of atmospheric pressure amplitude depends on the configurations of air resistance in the less permeable layer and the air-filled porosity difference in the two layers. The introduction of atmospheric pressure fluctuations into the airflow model leads to insignificant influence on water table level. A field application of the new solution at Hong Kong International Airport in Hong Kong, China is demonstrated. It indicates that the new transient solution can be conveniently used to evaluate the subsurface air pressure with discrete atmospheric pressure data at the ground surface. 相似文献
9.
Subsurface Airflow Induced by Natural Forcings 总被引：1，自引：0，他引：1
JiuJ．Jiao LIHai-long 《地球科学进展》2004,19(3):415-421
Subsurface airflow can be induced by natural processes,such as atmospheric or barometric pressure changes, water table fluctuations,topographic effects,and rainfall infiltration．Barometric pressure fluctuations are the most common cause of subsurface airflow,which can be significant under favourable geological conditions．This process has been studied most extensively because of its application to passive soil vapor extraction．Soil airflow induced by water table fluctuations can be significant,particularly where the fluctuations are of high frequency,for example,in tidal-influenced coastal areas．Top-ographic effects can lead to strong subsoil airflow in areas with great elevation differences．Rainfall infiltration usually produces only weak airflow.Air flow induced by these natural processes has important environmental and engineering implications．Among the different processes,airflow induced by tidal fluctuations has been studied the least,although it has exciting applications to coastal engineering projects and environmental remediation． 相似文献
10.
针对四川盆地大气污染防治工作的需要,应用2016年12月26日至2017年1月11日川南城市群（宜宾、自贡、泸州、内江、乐山）大气污染物浓度观测数据和气象数据,采用数理统计和污染天气诊断分析等方法,分析了这次川南城市群跨年度空气重污染过程的污染变化特征及其气象成因。结果表明：南支槽加强并引导其槽前西南干暖气流北上,致使当地低层大气增温,形成低空等温或逆温层,限制当地大气污染物扩散,是助长此重污染过程形成的主要天气系统。川南城市群低空的风向辐合,以及高相对湿度（未形成降水）所产生的吸湿增长效应,与低空等温或逆温配合,促使此次污染物浓度达到峰值（AQI为286）。南支槽减弱,随之原有等温或逆温层被破坏,逐渐减弱消失,低层风向辐合消失,川南城市群上空三维大气扩散能力增强,大气污染物浓度降低,最后降水的湿清除作用使当地污染物浓度快速降低,污染过程结束。本研究发现了有别于四川盆地西北部大气重污染的天气系统和相应气象成因,为深入认识川南城市群大气重污染气象成因及其防控提供了新的重要参考依据。 相似文献