Effect of different surface roughnesses on a turbulent boundary layer

Abstract

The classical treatment of rough wall turbulent boundary layers consists in determining the effect the roughness has on the mean velocity profile. This effect is usually described in terms of the roughness function delta U+. The general implication is that different roughness geometries with the same delta U+ will have similar turbulence characteristics, at least at a sufficient distance from the roughness elements. Measurements over two different surface geometries (a mesh roughness and spanwise circular rods regularly spaced in the streamwise direction) with nominally the same delta U+ indicate significant differences in the Reynolds stresses, especially those involving the wall-normal velocity fluctuation, over the outer region. The differences are such that the Reynolds stress anisotropy is smaller over the mesh roughness than the rod roughness. The Reynolds stress anisotropy is largest for a smooth wall. The small-scale anisotropy and interniittency exhibit much smaller differences when the Taylor microscale Reynolds number and the Kolmogorov-normalized mean shear are nominally the same. There is nonetheless evidence that the small-scale structure over the three-dimensional mesh roughness conforms more closely with isotropy than that over the rod-roughened and smooth walls

New Answers on the Interaction Between Polymers and Vortices in Turbulent Flows

“…Lastly, the interaction between polymers and turbulence is studied in each of the three spatial directions of space to isolate drag reducing and enhancing phenomena. The motivation of this work and the methodology employed is largely inspired by Prof. R. A. Antonia's work on the response of turbulent boundary layers to small perturbations of the boundary conditions, including roughness and suction, [1,3,4,10]. This work was presented at the conference organized in honor of Prof. Antonia 60th Birthday.…”

The turbulent boundary layer over transverse square cavities

“…Over the rough wall, ejections and sweeps are more intense than for a smooth wall layer. Measurements over three different types of surfaces (the so-called d-type roughness for which ∆U/U τ does not depend on the roughness height k, V-groove riblets aligned along the flow, and a k-type roughness for which ∆U/U τ depends on k) reported by Antonia (1994), indicated that the Reynolds stresses are increased relative to a smooth wall, with the exception of the riblet surface when it operates in a dragreducing mode. It was also noted that different changes to the turbulence structure occurred as a result of the different types of surface.…”

Thin liquid film entrainment by moving solids

“…With regard to the influence of surface roughness on the boundary layer structure and the formation of the liquid film as a result of its entrainment by the moving wire, several papers have been recently published, among them, Antonia and Krogstad (Antonia and Krogstad, 2000), Jiménez (Jiménez, 2004) and Akinlade (Akinlade, 2005).…”