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31.
重点介绍和讨论了中性条件下旋转扰动流体中边界层强迫不稳定及其相关的一些问题,阐述了旋转体系中切变驱动边界层不稳定的动力学特征.这些不稳定状态的研究在大气物理学、流体动力学、海洋学等多个领域中引起科学家极大的兴趣,近年来在实验和理论研究中都得到了不断的发展.意大利都灵大学基础物理系地球科学实验组通过水槽旋转实验方法,不断改变水槽启动或结束时的旋转运动速度,以及底部壁面粗糙度等要素,所得到的实验结果与SDBL理论非常一致. 相似文献
32.
粗糙度研究的现状及展望 总被引:23,自引:6,他引:23
略述边界层剪切湍流各区域速度廓线规律和地面粗糙分类后,对各种地面粗糙度(包括沙质粗糙度、动力粗糙度、植被粗糙度、复杂地面粗糙度、有效粗糙度)的研究现状和计算方法作了简要综述,认为动力粗糙度算式中系数A和植被或有效粗糙度算式中位移高度d将会是进一步研究的重点。 相似文献
33.
Yu Song 《Boundary-Layer Meteorology》1998,88(2):239-254
The Louis scheme for calculating the vertical eddy fluxes within the atmospheric surface layer is improved by broadening the original assumptions. In our approach, the momentum and heat transfer roughness lengths (z0 and zT respectively) can be different, and z0 need not be negligibly small compared with the lowest height (z) in modelling. For these conditions, we choose more consistent wind and potential temperature profile forms, then derive new algorithms for calculating fluxes. Improvement is demonstrated for a wide range of z/L (L is the Obukhov length), z/z0 and z0 zT, by comparing these fluxes with those derived from a theoretical surface-layer model. The improved algorithms can be used in atmospheric modelling systems for more varied surfaces and a wide range of atmospheric stability. 相似文献
34.
Mathias W. Rotach 《Boundary-Layer Meteorology》2001,99(3):379-410
35.
通过对四种参数化方法的比较,认为风海雷诺数RB较风速、波龄和波陡能更好地描述拖曳系数CDN。利用分组平均法对CDN与RB关系进行处理,得到最佳的CDN参数化方案。利用COARE3算法测试了四种依赖海况的粗糙长度,与实测结果进行了比较,结果表明CDN与RB的关系式更真实地反映了海-气界面动量交换过程。 相似文献
36.
Matthias Roth Jennifer A. Salmond A. N. V. Satyanarayana 《Boundary-Layer Meteorology》2006,121(2):351-375
We address some of the methodological challenges associated with the measurement of turbulence and use of scintillometers in the urban roughness sublayer (RSL). Two small-aperture scintillometers were located near the roof interface in a densely urbanized part of Basel, Switzerland, as part of the Basel Urban Boundary-Layer Experiment (BUBBLE) in the summer of 2002. Eddy correlation instruments were co-located near the mid-point of each scintillometer path for data verification purposes. The study presents the first values of the inner length scale of turbulence (l
0) and the refractive index structure parameter of air
for a city and demonstrates the influence of mechanical driven turbulence on dissipation. Comparison of dissipation values determined from the two approaches show large scatter that is possibly due to the spatial inhomogeneity of the turbulence statistics within the RSL. Velocity and temperature spectra display a −2/3 slope in the inertial subrange, although the spectral ratio is less than the theoretical prediction of 4/3 expected for isotropy. Conventional Monin–Obukhov equations used to calculate fluxes from the scintillometer were replaced with urban forms of the equations. The results suggest that the scintillometer may be an appropriate tool for the measurement of sensible heat flux (Q
H
) above the rooftops given a suitable determination of the effective measurement height. 相似文献
37.
A parametrization method used to account for the effects of flow separation and wall roughness on the lower boundary condition
for turbulent boundary layers is investigated against direct numerical simulation and laser Doppler anemometry data. The numerical
simulation represents flow over a smooth, flat surface with a prescribed external adverse pressure gradient. The water-channel
experiments cover flow over smooth and rough hills for two specified Reynolds numbers. Global optimization algorithms based
on four different direct search methods are used to assess the parametrization function, C, in terms of local mean velocity profiles and the parametrization parameters u
* (friction velocity), ∂
x
p (local pressure gradient), z
0 (effective roughness) and d (zero-plane displacement). The study investigates regions of attached and reversed flows, and forty-two velocity profiles
are compared with the proposed expression for the function C, including two profiles that satisfy the solution of Stratford. 相似文献
38.
The mean flow and scalar concentration profiles within and above a tall canopy are well known to violate the standard boundary-layer
flux-gradient relationships. We present a theory for the scalar concentration profile that is comprised of a canopy exchange
model coupled to a modified surface-layer model. The coupling between the two components and the modifications to the surface-layer
profiles are formulated through the mixing-layer analogy for the flow at canopy top. This analogy provides an additional length
scale—the vorticity thickness—upon which the profiles depend and a set of criteria that allows a reduction in the empiricism
associated with earlier forms in the literature. Predictions of the mean scalar concentration profiles are shown to match
observations over a wide range of diabatic stabilities for both potential temperature and water vapour. 相似文献
39.
Aerodynamic Parameters of Regular Arrays of Rectangular Blocks with Various Geometries 总被引:8,自引:8,他引:0
The aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment. Three aerodynamic
parameters characterising arrays—the drag coefficient (C
d
), roughness length (z
o) and displacement height (d)—are used for analysis. C
d
is based on the direct measurement of the total surface shear using a floating element, and the other two parameters are
estimated by logarithmic fitting of the measured wind profile and predetermined total drag force. The configurations of 63
arrays used for measurement were designed to estimate the effects of layout, wind direction and the height variability of
the blocks on these parameters for various roughness packing densities. The results are summarised as follows: (1) The estimated
C
d
and z
o of the staggered arrays peak against the plan area index (λ
p
) and frontal area index (λ
f
), in contrast with values for the square arrays, which are less sensitive to λ
p
and λ
f
. In addition, the square arrays with a wind direction of 45° have a considerably larger C
d
, and the wind direction increases z
o/H by up to a factor of 2. (2) The effect of the non-uniformity of roughness height on z
o is more remarkable when λ
f
exceeds 20%, and the discrepancy in z
o is particularly remarkable and exceeds 200%. (3) The effect of the layout of tall blocks on C
d
is stronger than that of short blocks. These results indicate that the effects of both wind direction and the non-uniformity
of the heights of buildings on urban aerodynamic parameters vary greatly with λ
p
and λ
f
; hence, these effects should be taken into account by considering the roughness packing density. 相似文献
40.
Arnaldo Longhetto Enrico Ferrero 张瑛 全利红 Massimiliano Manfrin Luca Mortarini Renato Forza 《气象与减灾研究》2009,32(3):15-18
重点介绍和讨论了中性条件下旋转扰动流体中边界层强迫不稳定及其相关的一些问题,阐述了旋转体系中切变驱动边界层不稳定的动力学特征。这些不稳定状态的研究在大气物理学、流体动力学、海洋学等多个领域中引起科学家极大的兴趣,近年来在实验和理论研究中都得到了不断的发展。意大利都灵大学基础物理系地球科学实验组通过水槽旋转实验方法,不断改变水槽启动或结束时的旋转运动速度,以及底部壁面粗糙度等要素,所得到的实验结果与SDBL理论非常一致。 相似文献