Direct numerical simulation of confined weak round fountains in homogeneous ambient

Abstract

Fountains (negatively buoyant jets) are commonly used in numerous engineering applications, such as the natural ventilation in buildings and the smoke spread in compartment fires. In this study, the long-term behavior of weak round fountains in homogeneous ambient confined in a cylindrical container was analyzed using three-dimensional direct numerical simulation over a range of the Froude number (Fr), Reynolds number (Re), dimensionless radius of the container (λ), respectively. The confined weak round fountain behaves in the manner of a ‘fountain filling box’ flow, experiencing five development stages, i.e., the formation of the fountain flow, the intrusion flow, the wall fountain, the reversed flow and the stratification. Three stages of the development of the bulk entrainment rate are identified and the dominant mechanisms involved are analyzed. Fr = 1 and 2 are identified as the approximate critical values to distinguish the behavior of the intrusion, wall fountain and stratification. Re = 200 is determined as the approximate critical value to distinguish the influence of Re. These are consistent with the existing results about the round fountains.