Turbulent Interaction of a Buoyant Jet with Cross-Flow: Fid-Bau Portal

Turbulent Interaction of a Buoyant Jet with Cross-Flow

de Wit, Lynyrd / van Rhee, Cees / Keetels, Geert

This paper presents large eddy simulations (LES) and experimental results of buoyant jets in cross-flow (JICF). Mixing behavior of buoyant JICF is governed by the velocity ratio ( $γ$ ) and the jet Richardson number (Ri). Four buoyant JICF cases are studied with $0.68 < γ < 1.28$ and $0.31 < Ri < 1.83$ . In this range, both initial buoyancy and initial momentum are important; the release of overflow dredging plumes is a practical example within this range. The shape, size, and vertical location of simulated jet concentration cross sections compare well to measured ones. The LES results are also compared with semiempirical formulas for buoyant JICF. Those formulas use an added mass coefficient ( $k_{n}$ ) and a spreading rate ( $β$ ) as calibration parameters. In the present study, it is found that path, dilution, and spreading can be well predicted by applying $k_{n} = 0$ and $β = 0.7$ ; those values result in better predictions than when using the advised values—namely, $k_{n} = 1$ , $0.34 < β < 0.62$ . Cross contours for concentration ( $C / C_{\max}$ ) and fluctuations ( $C^{'} / C_{\max}$ ) show self-similar behavior. The maximum value for a buoyant JICF is $C^{'} / C_{\max} = 0.45 - 0.65$ . The intriguing discovery is made that the jet of a buoyant JICF overtakes its own cross-flow: the average horizontal streamwise velocity of the jet of a buoyant JICF is slightly larger than the cross-flow velocity. This effect is found for all four buoyant JICF cases considered in this study, but is strongest for the deepest buoyant JICF trajectories. The increased horizontal streamwise velocity of the jet originates from zones with increased velocity next to the initially vertical jet, which acts as a vertical cylindrical obstacle.