Wall roughness effects in laminar flows: an often ignored though significant issue

• Published in: Experiments in fluids Vol. 49; no. 2; pp. 461 - 470
• Main Authors: Gloss, D., Herwig, H.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.08.2010; Springer
• Subjects: Applied fluid mechanics; Channels; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Entropy; Exact sciences and technology; Flows in ducts, channels, nozzles, and conduits; Fluid dynamics; Fluid flow; Fluid- and Aerodynamics; Fluidics; Fundamental areas of phenomenology (including applications); Heat and Mass Transfer; Instrumentation for fluid dynamics; Laminar boundary layers; Laminar flow; Laminar flows; Physics; Research Article; Roughness; Turbulence; Walls; Channel Height; Reynolds Number; Laminar Flow; Entropy Production; Roughness Element; Rough wall; Test facilities; Pipe flow; Skin friction; Digital simulation; Roughness; Pressure distribution; Entropy; Experimental study; Laminar flow; Groove; Microstructure; Microfluidics
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-009-0811-6

The effect of wall roughness, which is strong in turbulent flows often, is neglected in laminar flows, though without justification. With an experimental set-up which allows for changes in the relative roughness of a channel without requiring manipulation of the rough channel surface, it can be shown that there is a non-negligible influence of wall roughness even for laminar flows. Based on the consideration of entropy production in these flows, an increased dissipation rate in the vicinity of the roughness elements is identified as the physical mechanism that leads to an increased total head loss when the walls are no longer smooth.