United States Department of Transportation
i
New Models Account for Pavement Roughness in Analysis of Water Film Thickness for Assessing Hydroplaning Risk [fact sheet]
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2021-01-01
[PDF-1.11 MB]
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Abstract:In hydraulic engineering, the Manning’s roughness coefficient is often used to characterize surface roughness, and its values are either derived from experiments or assumed from empirical tables. In most computational fluid dynamics (CFD) software, the user must specify a roughness height parameter, ks, thus setting the equivalent sand–grain roughness height on a surface. The effective roughness height is limited to one half the height of the layer of computational cells adjacent to the road surface; beyond that, it has no effect. The height of cell layers in the analysis of water films is about 0.1 mm, limiting the roughness height to about 0.05 mm, which is far smaller than the range of roughness of road surfaces that may vary up to about 3.6 mm. Alternate approaches to treating roughness in the software are needed.
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