By Xiaojing Zheng
Mechanics performs a basic position in aeolian tactics and different environmental experiences. This proposed ebook systematically offers the hot development within the examine of aeolian strategies, specially within the examine on mechanism, theoretical modelling and computational simulation of aeolian procedures from the perspective of mechanics. these days, environmental and aeolian procedure comparable difficulties are attracting a growing number of realization. we are hoping this proposed publication will supply scientists and graduate scholars in aeolian examine and different environmental learn a few mechanical equipment and ideas and introduce aeolian similar difficulties of surroundings to mathematical and mechanical scientists.
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The exchange and transport processes determine the physical distribution and variance with time of physical quantities and the result is that the physical quantities will be transported from high-value area to low-value areas. Therefore, the subjects of interest in the observations of the boundary layer mainly include the following aspects: (1) the heat flux (such as latent heat flux, sensible heat flux): the heat arises from the solar radiation transported by turbulence from the ground to the boundary layer or from high temperature areas to low temperature areas; (2) the momentum flux: the momentum transferred from high wind power areas to low wind power areas, and mass of aerosol such as vapor and pollutants from high concentration area to low concentration area; and (3) fluctuating information of wind velocity and direction, correlation, flux and temporal and spatial distribution of the turbulence spectrum.
Moreover, the turbulence is a ‘burst’ process and has a large-scale eddy structure. The ‘burst’ process usually occurs in the viscous layer and buffer layer. Kline et al. (1967) found that, in the direction of flow, there naturally exist alternatively distributed low and high velocity stripes in the near wall area. The low velocity stripes gradually move downstream, moving further away from the wall and upward. Having reached the buffer layer, the stripes vibrate violently and eventually break into small-scale structures.
Large eddies in the boundary layer causes this burst to subsidence process, which is named by Kline et al. (1967) as coherent structure exhibit this process. For atmospheric boundary layer flows, Re ≈ 108 (Wyngaard 1992). Hence the atmospheric boundary layer flows are almost always turbulent. When the wind velocity in the open air exceeds 1 m·s–1, the air movement must be turbulent, no matter how smoothly the wind seems to pass by (Bagnold 1941). Therefore, the air flows which cause moving sand in the near surface layer are nearly all turbulent (Pettijohn et al.