Effects of rotation on flow in an asymmetric rib-roughened duct: LES study

We report on large-eddy simulations (LES) of fully-developed flow in a duct of a rectangular cross-section in which square-sectioned, equally-spaced ribs oriented perpendicular to the flow direction, were mounted on one of the walls. The Reynolds number, based on hydraulic di-ameter Dh, bulk velocity U0 and air properties, is 15,000. The duct was subjected to clock-wise (stabilizing) and anti-clock-wise (destabilising) rotation, at a moderate Rotational number, Ro=0.3. The LES results showed good agreement with the experimental results of Coletti et al. (2011) available in the mid-span plane. We analyzed the effects of stabilizing and destabilizing rotation on the flow, its vortical structures and turbulence statistics by comparing results of the rotating configurations with the nonrotating case with a focus on the im-portance of the secondary motions and the scales of the turbulent structures. To determine the existence of very long structures, we considered two different domains: a single rib spacing, confirmed in the experiment to be fully periodic after the 6th rib and a double domain extend-ing over two successive ribs. Comparisons of the two cases in terms of turbulence statistics and vorticity field confirmed no significant differences. The modifications of the turbulence intensity were interpreted on the basis of the rotation-induced production terms in the Reyn-olds stress equation.