Turbulent flow over irregular rough surfaces: statistical properties of the near-wall flow

Dr. Angela Busse (University of Glasgow)

Thursday 3rd November, 2016 14:00-15:00 Maths 522


Surface roughness occurs in many different forms in both engineering systems and the environment. The presence of roughness on a surface modifies the near-wall turbulent flow. Fluid dynamic roughness effects, such as the increase in the friction factor compared to the smooth wall case, grow as k+, the height of the roughness relative to the viscous length scale of the flow, increases.
The flow in the immediate vicinity and within the rough surface has received so far only little attention due to difficulties in obtaining well-resolved flow measurements close to rough surfaces.  In this talk I will discuss results from a series of direct numerical simulations (DNS) of turbulent flows over irregular rough surfaces based on typical examples of engineering rough surfaces.  The changes in the flow within and in the immediate vicinity of the roughness have been characterised for a range of k+ values. It emerges that the viscous sub-layer is replaced by a ‘blanketing’ layer as the rough-wall turbulent flow goes from the transitionally rough to the fully rough regime.

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