Journal ArticleDOI
Turbulent wind flow over a low hill
P. S. Jackson,J. C. R. Hunt +1 more
TLDR
In this article, an analytical solution for the flow of an adiabatic turbulent boundary layer on a uniformly rough surface over a two-dimensional hump with small curvature was presented for the limit L/y 0 → ∞ when h/L 2k2/ln(δ/y0) where L and h are the characteristic length and height of the hump, y0 the roughness length of the surface and δ the thickness of the boundary layer.Abstract:
An analytical solution is presented for the flow of an adiabatic turbulent boundary layer on a uniformly rough surface over a two-dimensional hump with small curvature, e.g. a low hill. The theory is valid in the limit L/y0 → ∞ when h/L 2k2/ln(δ/y0) where L and h are the characteristic length and height of the hump, y0 the roughness length of the surface and δ the thickness of the boundary layer. For rural terrain, taking δ ∼ 600m these conditions imply that 102 < L < 104m and h/L < 0·05. Considerations of the turbulent energy balance suggest that the eddy viscosity distribution for equilibrium flow near a wall may still be used to a good approximation to determine the changes in Reynolds stress. This result is only required in a thin layer adjacent to the surface - in the main part of the boundary layer the perturbation stresses are shown to be negligible and the disturbance to be almost irrotational. The theory shows that for a log-profile upwind the increase in wind speed near the surface of the hill is O((h/L)u0(L)) where u0(L) is the velocity of the incident wind at a height L. Thus the increase in surface winds can be considerably greater than is predicted by potential flow theory based on an upwind velocity u0(h). It is also found that, at the point above the top of a low hill at which the increase in velocity is a maximum, the velocity is approximately equal to the velocity at the same elevation above level ground upwind of the hill. The surface stress is highly sensitive to changes in the surface elevation, being doubled by a slope as small as one in five. The turning of the wind in the Ekman layer may induce a change in direction of the wind above the hill.
The main object of this analysis is to show how the changes in wind speed and shear stress are related to the size and shape of the hill and to the roughness of the surface. Some comparisons are made with measurements of the natural wind and wind tunnel flows. These suggest that the theory may be useful in giving rough estimates of the effect of hills on the wind. The theory and the quoted measurements suggest that the present design recommendation for the increase in wind speeds over hills to be used in wind loading calculations may be an underestimate. It is to be hoped that this analysis will encourage more detailed measurements to be made of the wind over hills.read more
Citations
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Journal ArticleDOI
The physics of wind-blown sand and dust
TL;DR: The physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices are reviewed.
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The physics of wind-blown sand and dust
TL;DR: In this article, an extensive review of the physics of wind-blown sand and dust on Earth and Mars is presented, including a review of aeolian saltation, the formation and development of sand dunes and ripples, dust aerosol emission, weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices.
Book ChapterDOI
The Influence of Mountains on the Atmosphere
TL;DR: In this article, a review of the meteorological phenomena associated with topography is presented and the theory of two-dimensional mountain waves with the help of its governing equations is presented.
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Physics and Modelling of Wind Erosion
TL;DR: In this paper, the Dynamics and Modelling of Saltation of Dust Emission, Dust Transport and Deposition, Integrated Wind-Erosion Modelling, Sand Dunes, Dynamics and Modeling, and Techniques for Wind Erosion Measurements are presented.
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Foredunes and blowouts: initiation, geomorphology and dynamics
TL;DR: A review of the initiation, dynamics, geomorphology and evolution of incipient foredunes, established foredune, and blowout is given in this paper, where the authors present a new model of the evolutionary paths at various possible time scales.
References
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Journal ArticleDOI
Handbook of Mathematical Functions
Mathematical Models of turbulence
Brian Launder,D. B. Spalding +1 more
TL;DR: In this article, turbulence and melange models are used to model models of mathematical models for fluides reference record created on 2005-11-18, modified on 2016-08-08.
Journal ArticleDOI
The analogy between streamline curvature and buoyancy in turbulent shear flow
TL;DR: In this paper, a formal algebraic analogy is drawn between meteorological parameters such as the Richardson number and the parameters describing the effect of rotation or streamline curvature on a turbulent flow.
Journal ArticleDOI
Wakes behind two-dimensional surface obstacles in turbulent boundary layers
TL;DR: In this paper, an analytical theory is deduced for the mean velocity behind a two-dimensional obstacle (of height h) placed on a rigid plane over which flows a turbulent boundary layer (of thickness δ).
Journal ArticleDOI
Laminar flow over a small hump on a flat plate
TL;DR: In this article, a boundary layer flows over a flat plate which has on it a small hump situated downstream of the leading edge, and the presence of the hump generates an interaction between the inviscid region just outside the boundary layer and the viscous region near the hump.