Comparison of three roughness function determination methods

• Published in: Experiments in fluids Vol. 35; no. 4; pp. 372 - 379
• Main Authors: SCHULTZ, M. P, MYERS, A
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01-10-2003; Berlin
• Subjects: Boundary layer and shear turbulence; Exact sciences and technology; Fluid dynamics; Fluid flow; Fundamental areas of phenomenology (including applications); Instrumentation for fluid dynamics; Painted; Physics; Rotating disks; Roughness; Similarity; Sprayers; Sprays; Turbulent flows, convection, and heat transfer; Turbulent flow; Error estimation; Skin friction; Rotating disk; Laser Doppler velocimeters; Roughness; Experimental study; Velocity measurement; Boundary layers
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/S00348-003-0686-x

Three methods have been used to experimentally determine the roughness function (?U +) for several rough surfaces. These include the rotating disk, the towed plate, and the velocity profile methods. The first two are indirect methods in as much as they rely on measurements of overall torque or resistance and boundary layer similarity laws to obtain ?U +, whereas the velocity profile method provides a direct measurement of ?U +. The present results indicate good agreement between the towed plate and the velocity profile methods for all of the surfaces tested. Tests for the rotating disk were carried out at much higher unit Reynolds numbers. Using this method, the results for sandpaper rough surfaces agree within their uncertainty with a Nikuradse-type roughness function in the fully rough regime, while a spray painted surface agrees with a Colebrook-type roughness function.