High-resolution numerical analysis of turbulent flow in straight ducts with rectangular cross-section

Abstract

Turbulent secondary motion of straight open duct flows with a rectangular cross-section was studied by means of direct numerical simulations, and the unique mean flow patterns were analysed with the aid of instantaneous coherent structure analysis for their Reynolds number dependence. Similar to the closed duct counterparts, it was found that the mean streamwise vorticity pattern is the statistical footprint of the most probable locations of the quasi-streamwise vortices. Furthermore, the existence of tightly-concentrated vortices with preferable rotational directions inside the mixed corners formed by no-/free-slip boundaries was observed. Such flow structures correspond to the side-wall high-speed streaks located directly on the free-slip plane, independently of Reynolds number, as well as the following low-speed streaks reside approximately 50 wall units away from the free-slip plane for friction Reynolds number larger than 200.