On the entrainment coefficient in negatively buoyant jets

Abstract

Integral models proposed to simulate positively buoyant jets are used to model jets with negative or reversing buoyancy issuing into a calm, homogeneous or density-stratified environment. On the basis of the self-similarity assumption, ‘top hat’ and Gaussian cross-sectional distributions are employed for concentration and velocity. The entrainment coefficient is considered to vary with the local Richardson number, between the asymptotic values for simple jets and plumes, estimated from earlier experiments in positively buoyant jets. Top-hat and Gaussian distribution models are employed in a wide range of experimental data on negatively buoyant jets, issuing vertically or at an angle into a calm homogeneous ambient, and on jets with reversing buoyancy, discharging into a calm, density-stratified fluid. It is found that geometrical characteristics such as the terminal (steady state) height of rise, the spreading elevation in stratified ambient and the distance to the point of impingement are considerably underestimated, resulting in lower dilution rates at the point of impingement, especially when the Gaussian formulation is applied. Reduction of the entrainment coefficient in the jet-like flow regime improves model predictions, indicating that the negative buoyancy reduces the entrainment in momentum-driven, negatively buoyant jets.

Advanced integral model for groups of interacting round turbulent buoyant jets

“…Visualisation results with round vertical interacting buoyant jets, one of which was dyed, as well as concentration measurements, validate the spreading concept [26,28]. This assumption restricts the model applicability and therefore AIM cannot be directly applied within spreading layers created due to an interface (free surface or terminal height of rise because of stratification), as those examined by [14,19,27]. The procedure followed to solve the system of momentum and tracer Eqs.…”

Characterization of scalar mixing in dense gaseous jets using X-ray computed tomography

“…Negatively buoyant inclined and horizontal jets have been previously studied, often in the context of submerged liquid discharges (Fan 1967;Jirka 2004;Papakonstantis et al 2011), but literature on such flows in gas-phase phenomena is sparse (Britter 1989;Wang and Andreopoulos 2010). Buoyancy effects in vertical jets, however, have been well characterized experimentally (Chen and Rodi 1980;Panchapakesan and Lumley 1993;Papaniclaou et al 2008;Pitts 1991).…”

Impacts of Brine Discharge on the Marine Environment. Modelling as a Predictive Tool

“…Kaminski et al, 2005, experimentally and theoretically studied turbulent entrainment in jets with arbitrary buoyancy. Papanicolau et al, 2008, studied the entrainment phenomenon in negatively buoyant jets. Alavian at al, 1992, expanded their study to a three-dimensional flow moving in a stratified environment.…”