Influence of the Reynolds number on the instant flow evolution of a turbulent rectangular free jet of air

Numerical solution of three-dimensional rectangular submerged jets with the evidence of the undisturbed region of flow

“…The present three-dimensional numerical results, validated against the theories of [3] and [4], confirm more than a decade of experimental observations about the URF in the average flow, and the NDF and SDF in the instantaneous flow, [14][15][16][17][18][19][20].…”

“…This is the main difference with the numerical results of the two-dimensional case, [1], where this region is not present, but the large eddies occupy the entire domain, forming an asymmetric pattern. The comparison of the present results with the two-dimensional case, [1], confirm that also in presence of a perturbation in the amplitude of the velocity profile there is a Negligible Disturbance Flow (NDF), immediately downstream the slot exit, where the jet height remains almost constant, followed by the Small Disturbance Flow (SDF), where the jet height evidences small contractions or expansions but without the formation of vortices, as observed experimentally in [20]. The sum of the length of NDF and SDF is about the same of the Undisturbed Region of Flow (URF), which has been defined for the average variables.…”

“…The aim of this work is to confirm the experiments of [14][15][16][17][18][19][20], that discovered the presence of a region of flow which can be considered "undisturbed" between the exit of the slot and the beginning of the PCR. This region, or type of flow, has been called Undisturbed Region of Flow, URF, in the average evolution, and Negligible Disturbance Flow, NDF, plus Small Disturbances Flow, SDF, in the instantaneous evolution.…”

“…A wall is present above and below the slot, with a thickness of 0.176 hydraulic diameters, as in the experiments [19][20]. The total pressure is imposed on the outlet boundaries, while the velocity boundary condition changes according to its direction.…”

“…(24) it follows that the value of the constant a can be deduced from the vertical velocity profile. Equations (20) and (22) are solved providing the boundary conditions imposed in [3] and [4]. The constants can be chosen in such a way that the variables ξ and ζ coincide.…”