Numerical investigation of bend and torus flows, part I : effect of swirl motion on flow structure in U-bend

Abstract

As a preliminary study to flow modeling in torus reactors, simulations are carried out in well-known standard geometries, namely 90° and 180° bends. For the latter, two flow configurations are considered, with and without initial swirl motion so as to approach torus reactor conditions. Efficiency of the commercial CFD code FLUENT is investigated by comparing predicted results with experimental measurements available in the literature for both bended configurations. Different turbulent models and near-wall considerations are considered, including k– ε and high Reynolds-stresses models, with the standard wall-function approach as well as the two-layer zonal model and low- Re k– ε models. After validation of the numerical strategy, a parametric study is made to better understand the interactions between Dean vortices, involved by the bend curvature, and the main rotating motion generated by the swirl motion. Simulations are achieved for various values of the initial swirl intensity applied at the bend entry. Numerical simulations show different flow structures, resulting from the progressive Dean vortices perturbations with the increase of swirl intensity.