Experiments on vertical plane buoyant jets in shallow water

Abstract

The paper reports on measurements of the flow generated by a plane buoyant jet discharging vertically into shallow water. The study comprises visualization experiments, mean-velocity and turbulence measurements with a two-channel laser-Doppler anemometer and temperature measurements with thermistor probes. According to the previous investigation of Jirka & Harleman (1979) (JH) the flow may be either stable with the heated discharge water leaving the near field in a warm water layer adjacent to the surface, or unstable with flow recirculation and re-entrainment of heated water into the jet. The stable situation usually involves an internal hydraulic jump associated with a roller. Both stable and unstable situations were investigated, the limiting case of a non-buoyant jet representing the unstable one. In order that a roller representing an internal hydraulic jump developed in the relatively short test channel in the buoyant situations, a strong downstream control had to be imposed by inserting a slightly submerged weir. Most experiments were carried out at a depth-to-discharge-width ratio of 100, and in this case the strong upstream control caused the hydraulic jump to be flooded for both of the densimetric Froude numbers studied (F = 9.9 and 21). In each case, a thick upper layer of nearly uniform temperature developed, with a larger layer thickness for F = 21. Below this layer was a relatively thin interface with temperature gradients and below this a counterflow of cold ambient water. For both Froude numbers, the flow was stable in the sense of JH, but only marginally so in the higher-Froude-number case. The observed trends of the flow behaviour follow the stability analysis of JH, but the dilution of the heated water, which was determined from the temperature measurements, is different from that predicted by the JH mixing analysis. The dilution is much lower in the present case with the flooded jump than in the JH analysis and experiments without specific downstream control and with a much longer test channel and thus no flooded jump.

SPH modeling of plane jets into water bodies through an inflow/outflow algorithm

“…At tðV 1 =D i Þ ¼ 54:6 and 70.2, the general horizontal movement of the flow motion leads to the occurrence of additional two recirculating cells having lower magnitude with respect to the cells close to the jet injection. This kind of process can also be observed in the cases of water-jet phenomena in unconfined conditions (without the presence of vertical walls) in which the development of more recirculating cells along the fluid domain is highlighted (Andreopoulos et al, 1986). As pointed out by the experiments of Espa and Frattini (2002) and Andreopoulos et al (1986), the horizontal length of the recirculating cells in the present SPH simulations has an extension which ranges between 2H s and 2.5H s .…”

“…Due to the presence of a shallow water ambient (low ratio between water depth of the tank and jet diameter), the zone of surface impingement is characterized by two small standing waves appearing beside the vertical motion of the jet (0:4 o x=L o0:6), as described in Espa and Frattini (2002) and Kuang et al (2001). In this case, the fluid is entrapped generating two recirculating counter-rotating cells (Andreopoulos et al, 1986) (see streamlines in Fig. 15).…”

“…Firstly, attention is paid to the study of two-dimensional jets propagating into water tanks, performing the analysis in shallow water environments, characterized by a low ratio between the water depth and the jet diameter (e.g., Andreopoulos et al, 1986). Successively, the evolution of a plane jet in the presence of a coexisting flow, as in the case of a channel flow, is considered.…”

Challenges in the management and regulation of large cooling water discharges

“…Several mechanisms have been proposed for generation of the vortices (Andreopoulis et al, 1986). In the case above, the vortices are part of a horseshoe-shaped vortex system caused by rotation around the rising plume in the near field that persists into the far field, gradually moving apart.…”

“…There appear to be no conclusive results defining the conditions under which bifurcation appears, but it is sensitive to a number of factors including discharge rate, buoyancy, outfall shape and diameter, and depth and velocity of the ambient fluid above the outfall (Andreopoulis et al, 1986;Jirka and Domeker, 1991;Smith and Mungal, 1998). In considering spreading of the plume observed at Sizewell A power station (Suffolk, UK), MacQueen (1978) concluded that vortices related to buoyancy were more likely to be significant than velocity shear at the outlet.…”