A computational fluid dynamic model that can solve the Reynolds-averaged Navier-Stokes equations and the species transport equation is developed to simulate two coalescing turbulent forced plumes, which are released with initial momentum and buoyancy flux into a linearly stable stratified environment. The velocity fields, turbulence structures, and entrainment of two plumes with different source separations and source buoyancy fluxes are analyzed quantitatively, in comparison with a series of physical experiments. An empirical parameterization is proposed to predict the amplification of the maximum rise height of two coalescing forced plumes caused by superposition and mutual entrainment. The maximum values of both turbulent kinetic energy and turbulence dissipation rate decrease monotonically with the increase in source separation of the two turbulent plumes. However, the trajectory of the maximum turbulent viscosity attained in the plume cap region presents two notable enhancements. This variation may be attributed to the turbulence transported from the touching region and the strong mixing around the neutrally buoyant layer between two plumes, while the mixing is caused by the lateral convection and the rebound after overshooting. The plume entrainment coefficient in near vent stems has a positive relationship with the source Richardson number. A transition of flow regimes to plume-like flows would occur when the contribution of initial momentum is important. The entrainment coefficient will decrease in the touching region of two plumes due to mutual entrainment, while the superposition of plumes can lead to distortion of the boundary of plume sectors.

Horizontal warm buoyant jets injecting into a linearly stratified ambience are common in lakes, estuaries, and oceans. Dynamic features and potential surface temperature signatures of heated buoyant jets are experimentally investigated using particle image velocimetry and an infrared camera. Results reveal that when heated jets are completely underwater, the flow evolution can be classified into the horizontal regime, ascending regime, and collapsing regime, respectively. The maximum rise height and the neutral height both increase linearly with the increasing jet length scale. Based on this relationship, an equation is developed to predict the surface impingement of a horizontal heated buoyant jet. If the surface impingement occurs, staggered vortexes and large meanders caused by mixing between the jet and the free surface are observed on the surface temperature maps. Furthermore, surface temperature fluctuation fields are decomposed using the Karhunen-Loeve method, the first four eigenmodes appear to capture the root mean square temperature fluctuations and the features correlated with the swirling vortexes. In the turbulent kinetic energy budget, mean-flow convection is found to be mainly balanced by turbulent transport. As the heated jet propagates downstream, more kinetic energy is transferred into potential energy rather than into turbulent energy.

Transport and deposition behavior of mineral particles driven by hydrothermal plumes along mid‐ocean ridges is one of the least understood processes in geoscience. We reveal the mechanism and three typical transport patterns of particles emitted from submarine vents and subsequently laden by plumes in the stratified deep ocean with or without crossflows, that is, suspension, near‐vent deposition, and long‐distance transport, by developing a Lagrangian model coupled with a computational fluid dynamics model and using in situ measurements as model inputs. The particle trajectories suggest a general expression that predicts a linear variation of deposition location with the reciprocal of settling velocity, which potentially leads to a power law distribution of sediment mass along the radial direction. Our findings provide a new perspective on the accumulation of sediments near hydrothermal vents, indicating a critical role of the entrainment of plumes and consequent vortex systems in controlling deposition flux.

An integral model is developed to describe the merging of multiple forced plumes released from sources arranged evenly around a circle against a linearly stratified background. The velocity potential of an array of line sinks is introduced to identify the distorted boundaries of interacting plumes. The variation of the entrainment coefficient for forced plumes is modeled as a function of the local Richardson number in the model and an improved entrainment assumption based on the boundary-curvature analysis is proposed to regulate the merging. The present model is shown to be feasible to provide a self-consistent prediction for the dynamics of multiple coalescing forced plumes. The amplification of the maximum rise height of two plumes due to superposition is faithfully reproduced and its scaling predicted by the model is reasonably consistent with the observations of available experiments. The model results further suggest that the mean entrainment efficiency per unit length of the plume boundary attains a local minimum at the touching height, implying significant mutual entrainment in that region.

A RANS-based computational fluid dynamic model is developed to simulate the propagation and turbulent mixing of hydrothermal plumes in a stratified deep-sea environment and it is employed to study the Daxi hydrothermal field (DHF), Carlsberg Ridge in the Indian Ocean. Based on the results of in-situ measurements of the hydrothermal plume in the DHF, the parameter sensitivity is analyzed to evaluate the effects of the volume flux released from the vent orifice and the ambient buoyancy frequency on the plume dynamics. The results reveal the three-layer velocity field and obtain several important scalings, including the maximum plume rise height and neutrally buoyant plume height. Thus, it can be concluded that the classical entrainment assumption is applicable only to the plume stem below 0.6 times of the maximum plume rise height, and above that level, the structure of the flow field tends to be complicated due to the lateral spreading in the neutrally buoyant layer and circulation in the plume cap region. In addition, the simulation results show that both turbulent kinetic energy and turbulence dissipation rate attain their maximum values near the vent. However, the maximum turbulent viscosity is observed in the plume cap region, indicating strong turbulent mixing in that region. A quantitative analysis of the hydrothermal plumes in the DHF is performed by the proposed model and verified by the in-situ measurements, and the results suggest that the discrete heat flux of the DHF is about 39.38 MW. The proposed model can provide useful information for tracing the submarine hydrothermal vents, studying the matter and energy cycling in the ocean basin, and the exploration of submarine polymetallic sulfides resources and environmental assessment.

Horizontal buoyant jets in stratified fluids are investigated by employing a computational fluid dynamic model validated by experimental data. The characteristics of time mean flow, turbulence, and entrainment are quantified. We observed that turbulence parameters such as the turbulent kinetic energy, the turbulence dissipation rate, and turbulent viscosity attained their maximum values in the horizontal region. Here, the entrainment coefficient also reaches the maximum due to the instantaneous instability of the flow. The ascent region consists of the acceleration and deceleration stages due to the stratified ambience reversing the sign of buoyancy flux. In the acceleration ascent region, the entrainment coefficient stabilizes around 0.05. In the deceleration stage, the transition of the flow regime from plume- to jet-like regulates the entrainment. At the end of the ascent region, the jet reaches the maximum rise height (H_max), which can be well predicted by a semiempirical function at a given Richardson number, buoyancy frequency, and Reynolds number. An enhancement of turbulent parameters is observed near the H_max and could be attributed to overshooting and shearing between the up- and downflow. Analysis of density and velocity profiles shows the heavy fluids on the lower side of the jet core vertically separating from the center fluids, which drifted the velocity profile from a Gauss to a fat-tailed distribution and broke the self-similarity.