Abstract
Abstract
Highlights
There have been a number of recent papers exploring the nature of the flow in either a boundary layer or a channel when the wall surface contains longitudinal ribs whose height h is not a very small fraction of the boundary layer thickness, δ
An example of the kind of flow produced is shown in figure 1(a), which is from Hwang & Lee (2018), who used direct numerical simulation (DNS) to compute a developing boundary layer flow over longitudinal roughness
In view of some of the results shown later, it should be mentioned that the ribs were introduced using an immersed boundary-type method (IBM), based on the technique proposed by Goldstein, Handler & Sirovich (1993)
Summary
There have been a number of recent papers exploring the nature of the flow in either a boundary layer or a channel when the wall surface contains longitudinal ribs whose height h is not a very small fraction of the boundary layer thickness, δ (or, in the case of a channel, the half-height, H). By presenting numerical studies of nominally two-dimensional (2-D) smooth-wall channel flow with smooth-wall longitudinal ribs, this paper seeks mainly to complement these earlier works, including comparisons where appropriate and exploring inter alia the effect of the rib spacing with respect to rib width, S/W and domain (or boundary layer) height, H/S (see figure 1b), and Reynolds number. In all cases, including the present, it turns out that the profiles lie significantly below the usual log-law line expected in regular smooth-wall channels and, not unnaturally, have a ‘kink’ at the rib height (i.e. at z = h) This will be explored here, but it is worth noting immediately that the profiles obtained at specific spanwise locations in laboratory experiments lie below the regular log-law, as shown by Medjnoun et al (2020) and Zampiron et al (2020).
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