The wind-shade roughness model for turbulent wall-bounded flows.

Meneveau, Charles; Hutchins, Nicholas; Chung, Daniel

To aid in prediction of turbulent boundary layer flows over rough surfaces, a new model is proposed to estimate hydrodynamic roughness based solely on geometric surface information. The model is based on a fluid-mechanics motivated geometric parameter called the wind-shade factor. Sheltering is included using a rapid algorithm adapted from the landscape shadow literature, while local pressure drag is estimated using a piecewise potential flow approximation. Similarly to evaluating traditional surface parameters such as skewness or average slope magnitude, the wind-shade factor is purely geometric and can be evaluated efficiently from knowing the surface elevation map and the mean flow direction. The wind-shade roughness model is applied to over 100 different surfaces available in a public roughness database and some others, and the predicted sandgrain-roughness heights are compared with measured values. Effects of various model ingredients are analysed, and transitionally rough surfaces are treated by adding a term representing the viscous stress component.

POTENTIAL flow; ROUGH surfaces; GEOMETRIC surfaces; TURBULENT flow; DATABASES

Journal of Fluid Mechanics, 2025, Vol 1003, p1

0022-1120

Academic Journal

10.1017/jfm.2024.971