Uhlmann, MarkusPinelli, AlfredoKawahara, GentaSekimoto, Atshushi2023-06-202023-06-2020070022-1120https://hdl.handle.net/20.500.14352/50708A direct numerical simulation of turbulent flow in a straight square duct was performed in order to determine the minimal requirements for self-sustaining turbulence. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, corresponding to a friction-velocity-based Reynolds number of 80. The minimum value for the streamwise period of the computational domain is around 190 wall units, roughly independently of the Reynolds number. We present a characterization of the flow state at marginal Reynolds numbers which substantially differs from the fully turbulent one: the marginal state exhibits a four-vortex secondary flow structure alternating in time whereas the fully turbulent one presents the usual eight-vortex pattern. It is shown that in the regime of marginal Reynolds numbers buffer-layer coherent structures play a crucial role in the appearance of secondary flow of Prandtl's second kind.engjournal articlehttp://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=1346008http://www-thermomech.me.es.osaka-u.ac.jp/~kawahara/index.files/UPKS07.pdfopen access531Near-wall turbulencenumerical-simulationrectangular ducttransitionvorticessolversFísica (Física)22 Física