Preliminary numerical solutions of the evolution of free jets. IMECE2012-86730

Abstract

The present paper presents preliminary numerical solutions of the flow evolution of a two dimensional rectangular free jet. The numerical simulations in a two-dimensional domain are carried out with Open-FOAM, the open-source code, and compare the numerical results with the experimental visualizations performed in the same laboratory with the shadowgraph technique. The evolution of a two-dimensional submerged free jet is reported in the literature by the presence of two regions of flow: the potential core, where the centerline velocity maintains equal to that on the slot exit, and the turbulent or mixing region, where the centerline velocity decreases with the distance from the exit. Previous anemometric measurements, carried out in this laboratory with an air jet emerging from a rectangular channel, showed the presence of a region of flow, just outside the exit and before the potential core, where velocity and turbulence remain almost equal to those measured on the exit, and it has been called “undisturbed region of flow” because is present also in turbulent conditions. Previous and present shadowgraph visualizations show a jet which has the same height along the undisturbed region of flow and increases its height afterwards. The length of the undisturbed region depends on the Reynolds number of the flow and on the presence of turbulence promoters, e.g. metallic grids, at the exit of the slot. The undisturbed region is becoming nil with the increase of the Reynolds numbers, in agreement to the literature. The present two dimensional numerical solutions, carried out at Re numbers equal to 25,000 and 60,000 confirm the results obtained with the shadow visualizations