排序方式: 共有6条查询结果,搜索用时 0 毫秒
1
1.
This study focuses on the inertial oscillation aspect of the nocturnal low-level jet (NLLJ). In the context of the Ekman model solutions, conceptual NLLJ inertial oscillation analytical frameworks proposed by Blackadar in 1957 and Shapiro and Fedorovich and van de Wiel et al. in 2010 are compared. Considering a NLLJ produced via direct numerical simulation over flat terrain with no baroclinic influence as a reference case, the deficiencies of each framework in representing a realistic NLLJ are assessed. The Blackadar theory results in unrealistic wind profiles near the surface. While extensions of Blackadar’s framework by Shapiro and Fedorovich and van de Wiel et al. produce more realistic NLLJs, the simpler approach taken by van de Wiel et al. does not describe the NLLJ wind hodograph at later times sufficiently in qualitative terms. 相似文献
2.
Simon L. Axelsen Alan Shapiro Evgeni Fedorovich Han van Dop 《Environmental Fluid Mechanics》2010,10(4):387-414
An analytical model for katabatic flow induced by cold strip of finite width in the cross-slope direction but of infinite
extent in the downslope direction is presented. The fluid is assumed to have a constant (eddy) viscosity, and the Coriolis
force is neglected. A numerical simulation has been used to verify the model, which is shown to revert to the classical Prandtl
model if the strip width goes to infinity. The effects of the strip width and slope angle on the katabatic flow are studied.
The buoyancy and downslope velocity reach maximum values at the centre of the strip, and spread outwards in the cross-slope
direction. The downslope wind maximum weakens for narrow strips and shallow slopes. In contrast to the Prandtl solution, which
shows a counter flow above the wind maximum, our model predicts the counter flow to occur outside the strip. The cross-slope
variation in the surface forcing induces cross-slope and slope-normal velocities, which are manifested in vortices at the
strip edges. Below the wind maximum, the fluid above the cooling surface descends and moves toward the strip edge where it
is detrained from the strip region. Replenishment of fluid into the strip region takes place above the wind maximum. 相似文献
3.
Di Sabatino S. Kastner-Klein P. Berkowicz R. Britter R.E. Fedorovich E. 《Environmental Fluid Mechanics》2003,3(2):129-143
The modelling of pollutant dispersion at the street scale in an urban environment requires the knowledge of turbulence generated by the traffic motion in streets. In this paper, a theoretical framework to estimate mechanical turbulence induced by traffic in street canyons at low wind speed conditions is established. The standard deviation of the velocity fluctuations is adopted as a measure of traffic-produced turbulence (TPT). Based on the balance between turbulent kinetic energy production and dissipation, three different parameterisations for TPT suitable for different traffic flow conditions are derived and discussed. These formulae rely on the calculations of constants that need to be estimated on the basis of experimental data. One such estimate has been made with the help of a wind tunnel data set corresponding to intermediate traffic densities, which is the most common regime, with interacting vehicle wakes. 相似文献
4.
Environmental Fluid Mechanics - We obtain an analytical model solution to an idealization of an urban heat island (UHI) circulation—the steady shallow convective flow of a viscous stably... 相似文献
5.
Petra Kastner-Klein Evgeni Fedorovich Jean-Fran Ois Sini Patrice G. Mestayer 《Environmental monitoring and assessment》2000,65(1-2):353-361
In urban conditions, car exhaust gases are often emitted inside poorly ventilated street canyons. One may suppose however that moving cars can themselves produce a certain ventilation effect in addition to natural air motions. Such ventilation mechanism is not sufficiently studied so far. A similarity criterion relating the vehicle- and wind-induced components of turbulent motion in an urban street canyon was proposed in 1982 by E. J. Plate for wind tunnel modelling purposes. The present study aims at further evaluation of the criterion and its applicability for a variety of wind and traffic conditions. This is accomplished by joint analyses of data from numerical simulations and wind tunnel measurements. 相似文献
6.
Kastner-Klein Petra Fedorovich Evgeni Ketzel Matthias Berkowicz Ruwim Britter Rex 《Environmental Fluid Mechanics》2003,3(2):145-172
The paper addresses the problem of the parameterisation of traffic induced turbulent motion in urban dispersion models. Results from a variety of full-scale and wind-tunnel studies are analysed and interpreted within a modelling framework based on scaling considerations. The combined effects of traffic and wind induced dispersive motions are quantified for different traffic situations (variable traffic densities, vehicle velocities and vehicle types) and incorporated into the developed parameterisations. A new dispersive velocity scale is formulated and recommendations regarding its application in urban dispersion models are given. The necessity of accounting for traffic induced air motions in predictions of street-canyon pollution levels is demonstrated. Further research is needed to verify the empirical constants in the proposed parameterisations and to generalize the developed approach for a broader range of urban building configurations, meteorological conditions, and traffic situations. 相似文献
1