Formation and turbulent breakdown of large-scale vortical structures behind an obstacle in a channel at moderate Reynolds numbers

Abstract

This paper deals with experimental investigation and direct numerical simulation of three-dimensional separated laminar and transitional flows behind a semicircular spanwise rib on a bottom wall of a rectangular channel at Reynolds numbers of up to 480. Particular emphasis is given to the formation mechanism of quasiperiodic large-scale vortex clouds in the mixing layer behind the rib. Vortical structures near the channel axis are formed due to pairing of spiral vortices emerging close to the vertical walls when the corner boundary layers impact on the rib. The effect of the Reynolds number and normalized channel size on the spiraling motion, generation, and shedding of large-scale vortex clouds has been estimated.

On the highly unsteady dynamics of multiple thermal buoyant jets in cross flows

“…This companion subject relating to flows over and around wall-mounted obstacles has attracted significant interest over recent years owing to its important technical and industrial applications (related results are useful to improve the designs of the internal surfaces of pipes and a variety of heat exchangers, e.g., gas turbine blade cooling passages and serpentine cooling channels, advanced gas-cooled nuclear reactor fuel elements, solar collectors and cooling systems for electronic devices). There are indeed numerous valuable publications in which 'flow interruption' created in flow passages at periodic intervals (by means of ribs with various possible shapes) was intentionally used to promote turbulence and/or enhance convective heat transfer in ducts and channels (these roughness elements can invariably promote flow reversal in the gaps between them thereby breaking the laminar sub-layer of the internal flow, see, e.g., Refs [46][47][48][49][50][51][52]). This is the reason why these elements are also known as "turbulators".…”