Influence of an Exit Wall Boundary on the Flow of a Circular Jet.

The flow of the axisymmetric jet constitutes a subject of research from the origins of fluid dynamics; however it remains a subject of interest due to the recent findings that denote the influence of flow and geometry conditions in configurations that diverge from the theoretical "free-jet" case. In the present study, the effect of a wall boundary produced by a circular disk of twice the jet diameter, which is imposed on the exit of the jet is investigated experimentally and numerically. Computational simulations are performed to predict the flow characteristics incorporating different turbulence models (k-ε and Reynolds Stress) and solvers (Simplec and Coupled). Supportive pressure measurements are used to evaluate the predictions within the initial region of a circular jet at two Reynolds numbers (50,000 and 65,000). The results indicate that the presence of the exit wall boundary results to the formation of recirculation zone behind the exit, which prevents the entrainment of ambient fluid. Comparing with the flow field of the free from confinement jet, it is shown that the imposition of the wall has a minor effect on the mean velocity field; it is however capable of altering the turbulent flow properties, including the normal and the Reynolds shear stresses, in the region before the establishment of the self-similarity zone. [ABSTRACT FROM AUTHOR]