Drag of a turbulent boundary layer with transverse 2D circular rods on the wall

Abstract

between the boundary layer developing over this wall and the smooth-wall turbulent boundary layer.

Self-preservation in a zero pressure gradient rough-wall turbulent boundary layer

“…This result has been further corroborated for a turbulent boundary layer by the DNS study of Lee & Sung (2007). Experimentally, Kamruzzaman et al (2015) showed that the pressure drag contributed almost totally to the total drag on a rod-roughened wall with λ/k = 8. Removing the viscous term from (2.8) amounts to dropping (2.9h), while all other conditions remain valid.…”

“…In the present study, the situation is different as the cylinders are attached to a wall. However, recent observations by Kamruzzaman et al (2015) showed that the pressure distribution around a single cylinder element remained essentially identical over a range of Re, which is consistent with approximately constant C d . For smooth walls, the spatial averaging is not required and thus the dispersive Reynolds stress and the drag forces vanish from (2.1b).…”

“…This would correspond to the case where it is negligible everywhere in the boundary layer. This is likely to be observed on a rough wall made of transverse bars (Leonardi et al 2003;Kamruzzaman et al 2015). Leonardi et al (2003) showed that, relative to a smooth surface, the local viscous friction increases on the roughness top plane and becomes smaller between the roughness elements.…”

Turbulent Boundary Layer over various 2D Uniform Distributed Roughness Elements

“…By correlating them together, we can get an estimated value of the equivalent sand grain roughness height, which is a direct function of the roughness function. 7; TBL Data over rods from Djenidi [1] and TBL data over rods from Kamruzzaman [5]. The equation used to predict the k s :…”

“…The roughness function as a function of equivalent sand grain roughness height, normalised by inner length scale U τ /ν Figure 7 shows the roughness function ∆U + as a function of the equivalent sand grain roughness k + s in a fully rough regime. The results presented are the measured k + s from the velocity profiles over the rough surfaces; the predicted k + s from the k sk and ES, which have a larger marker size in figure7; TBL Data over rods from Djenidi[1] and TBL data over rods from Kamruzzaman[5]. The equation used to predict the k s :…”