Roughness sublayer

Figure 1.10 Schematic wind distribution over an urban territory after Bottema, 1993 [71] and Fisher et al., 2005 [193] 1 - logarithmic portion high enough over the city 2 - decelerated and distorted velocity profile within the urban canopy 3 - transition layer (roughness sublayer).

Kastner-Klein, P., Rotach, M and Fedorovich, E. (2000) Experimental study on mean flow and turbulence characteristics in an urban roughness sublayer, in Proceedings of 14th AMS Symposium on Boundary Layers and Turbulence, Aspen, CO, August 7-11, 2000. 

Kastner-Klein, P., and Rotach, M.W. (2004) Mean Flow and Turbulence Characteristics in an Urban Roughness Sublayer, Boundary-Layer Meteorology Vol. Ill, 55-84. 

Rotach, M.W.(1999) On the influence of the urban roughness sublayer on turbulence and dispersion, Atmospheric Environment 33, 4001 008. 

For Ti (z), the principle of the parameterization is that ii,TJLg is constant with height within the canopy (except very close to the ground) and in the roughness sublayer. This is a consequence of the mixing-layer analogy. Constancy of u.TJL leads to two alternative parameterizations... 

The changing character of the flow in the different regions of the turbulent boundary layer explains certain aspects of the friction factor chart. If the absolute roughness of the pipe wall is smaller than the thickness of the viscous sublayer, flow disturbances caused by the roughness will be damped out by viscosity. The wall is subject to a viscous shear stress. Under these conditions, the line on the friction factor chart... 

Owen Thomson (1963) analysed heat and mass transfer from rough surfaces in terms of a parameter B, termed the sublayer Stanton number, defined by the equation... 

Any iiregiilarily or roughness on the surface disturbs- the laminar sublayer, and affects the flow. Therefore, unlike laminar flow, the friction factor and the convection coefficient in turbulent flow are strong functions of surface roughness. 

Jayatilleke CLV (1969) The Influence of Prandtl Number and Surface Roughness on the Resistance of the Laminar Sublayer to Momentum and Heat Transfer. Prog Heat Mass Transfer 1 193-329... 

Surface Roughness. Up to this point, the turbulent boundary layer has been assumed to form on a surface that is aerodynamically smooth, namely, a surface whose roughness elements are small compared with the thickness of the viscous sublayer. As many surfaces in practical appli-... 

For the case of a surface with roughness elements of height e, one can repeat the analysis used in the previous section for a smooth surface. In this case there is no laminar sublayer so we do not need to use the kinematic viscosity in our analysis. On the other hand, we do need to add the height of the roughness elements. Thus the five parameters for the dimensional analysis are now dux/dz, e, p,z, and ut. One can then show that... 

For a rough surface, there is no laminar sublayer. Thus u should depend on tq, p, e, and. 13. By dimensional analysis, we reason that... 

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