Experimental characterization of three-dimensional flow vortical structures in submerged hydraulic jumps

Abstract

The characteristics of three-dimensional vortical flow structures in submerged hydraulic jumps (generated downstream of a sluice gate) are analyzed in this paper. Results of a careful experimental investigation of the mean flow as well as turbulence statistics obtained with the use of Acoustic Doppler Velocimetry (ADV) and Particle Tracking Velocimetry (PTV) are presented and discussed. Experiments encompass incident Froude numbers (Fr1) of 3, 4 and 5, and submergence factors (S) ranging from 0.18 to 1.04. First, distributions in three vertical planes of values of the stream-wise velocity component and turbulent kinetic energy (TKE) are shown. With this information, the influence of Fr1 and S on turbulence statistics is assessed. For the first time to the best of our knowledge, an approximately self-similar behavior of the profiles of TKE in the fully-developed region of the submerged jump is reported herein. A “climb effect” in the TKE is identified, very much in agreement with what occurs with the velocities. Then, the analysis focuses on the zone located near the gate, aiming at explaining the physical mechanisms which are responsible for the vorticity of vertical axis in that area. A relationship between the length scale of the roller of horizontal axis (Lrsj) and that of the vortices of vertical axis (Lv) is introduced, revealing that the dynamics of the two vortices are strongly linked. Compelling evidence sustaining that vorticity of vertical axis appears as a consequence of boundary-layer separation associated with the lateral walls is also provided. Finally, the anisotropy of turbulence in the outskirts of the vertical vortices is addressed, finding that such anisotropy is a consequence rather a cause of the presence of the vortices.