Measurements in the near-wall region of a boundary layer over a wall with large transverse curvature

• Published in: Journal of fluid mechanics Vol. 664; pp. 33 - 50
• Main Authors: KRANE, M. H., GREGA, L. M., WEI, T.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.12.2010
• Subjects: Boundary layer; Boundary layer and shear turbulence; Boundary layers; Curvature; Cylinders; Digital particle image velocimetry; Exact sciences and technology; Fluid dynamics; Fluid mechanics; free shear layers; Free surfaces; Fundamental areas of phenomenology (including applications); hydrodynamic noise; Instrumentation for fluid dynamics; Mathematical analysis; Measurement techniques; Physics; Position (location); Shear strength; Shear stress; Surface water; turbulent boundary layers; Turbulent flow; Turbulent flows, convection, and heat transfer; Uniform flow; Velocity; Walls; turbulent boundary layers; hydrodynamic noise; free shear layers; Reynolds stress; Water tunnel; Test facilities; Turbulent flow; Shear stress; Circular cylinder; Particle image velocimetry; Experimental study; Velocity measurement; Curvature; Boundary layers; Turbulence structure
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/S0022112010003770

Measurements of the near-wall velocity field of the flow over cylinders aligned with a uniform flow are presented. The broader objective of this investigation was to quantify and understand the role of transverse curvature in the limit as cylinder diameter approaches zero. The specific goal was to begin with a turbulent boundary layer over a larger radius cylinder and see what happens as the radius is reduced. Spatially and temporally resolved digital particle image velocimetry (DPIV) measurements were made on three different radius cylinders, 0.14 cm ≤ a ≤ 3.05 cm, extending along the length of a large free-surface water tunnel. Mean and fluctuating profiles are presented at a fixed streamwise location and free-stream speed. For the first time, spatially resolved measurements were made very close to the wall, permitting direct determination of wall shear stress, i.e. uτ, from near-wall velocity profiles. The measurements revealed a region close to the wall for small radii where the mean streamwise velocity profile is inflectional. This has significant implications on assumptions regarding what happens in the limit of a vanishing cylinder radius.