Buoyant Jet Model Research Articles

Research on hydrogen leakage and dispersion characteristics in indoor thermal stratification environment

The leakage of hydrogen in a room is a key issue of hydrogen safety, and ventilation plays an important role in hydrogen dispersion. The hydrogen leakage usually builds a thermal stratification environment due to the low temperature of liquid hydrogen or throttling effect. This study attempts to develop a fast-computational theoretical model of hydrogen dispersion motion in an indoor thermal stratification environment based on the classical buoyant jet model and to carry out an experimental to verify model. The research results show that the developed theoretical model can well predict the trajectory of slowly releasing hydrogen leakage. The motion trajectory of the hydrogen leak oscillates in the thermally stratified environment at a certain height, called as the “lock height”. The smaller the leak port in the uniform environment the larger the horizontal diffusion distance, and the smaller the leak port in the thermally stratified environment the higher the locking height. The research results are expected to predict the hydrogen leakage safety prediction problem and the formulation of related standards and help make ventilation strategies to ensure the hydrogen safety.

Combined integral and particle model for describing the dispersion, dilution, terminal layer formation and influence area from a point source discharge into a water body

Contamination of coastal water is a persistent threat to ecosystems around the world. In this study, a novel model for describing the dispersion, dilution, terminal layer formation and influence area from a point source discharge into a water body is presented and compared with field measured data. The model is a Combined Integral and Particle model (CIPMO). In the initial stage, the motion, dispersion and dilution of a buoyant jet are calculated. The output from the buoyant jet model is then coupled with a Lagrangian Advection and Diffusion model describing the far-field. CIPMO ensures that both the near- and far-field processes are adequately resolved. The model either uses empirical data or collects environmental forcing data from open source hydrodynamic models with high spatial and temporal resolution. The method for coupling the near-field buoyant jet and the particle tracking model is described and the output is discussed. The model shows good results when compared with measurements from a field study.

Integral model of a reacting chlorine jet in ammonia nitrogen and treated primary effluent

Chlorine is extensively used in disinfection processes in water and wastewater treatment processes. The chlorine is typically dosed by jet mixing, and yet no systematic study of chlorine jets has been conducted. In the Stonecutters Island Sewage Treatment Works (SCISTW) of the Hong Kong Harbour Area Treatment Scheme (HATS), concentrated chlorine solution (in sodium hypochlorite form) is injected into primary treated effluent in the form of turbulent dense jets. In view of the importance of sewage disinfection to the environmental impact, it is essential to understand the mixing and reaction of chlorine with ammonia nitrogen for disinfection dosage optimization. In this study, an integral buoyant jet model is developed for a chlorine jet reacting with ammonia nitrogen in CEPT sewage. The jet mixing and chlorine demand is studied by accounting for the stoichiometric reaction of chlorine and ammonia including breakpoint chlorination. Based on experiments of chlorine jet in ammonia solution, the stoichiometric mass ratio of chlorine to ammonia under dynamic mixing process is found to be 7.48. The chlorination kinetics model is then incorporated in a general model of a chlorine jet discharging into a coflowing primary treated sewage effluent, with the reaction ratio calibrated based on experimental measurements for the stagnant case. Significant chlorine demand can occur within a short distance (in the order of 0.1 m, or 1 s or less of travel time) from the dosing point due to the turbulent mixing and reaction with ammonia nitrogen and organic impurities. The chlorine demand of CEPT effluent increases with jet dosing total residual chlorine (TRC) concentration. At TRC < 2000 mg/L, the chlorine demand of sewage is mainly due to ammonia nitrogen (>60%), while for TRC ≫ 2000 mg/L, up to two thirds of chlorine demand can be induced by the oxidation of organic debris. Model predictions of chlorine demand and concentration agree well with laboratory experiments and field data.

A second-order integral model for buoyant jets with background homogeneous and isotropic turbulence

Buoyant jets or forced plumes are discharged into a turbulent ambient in many natural and engineering applications. The background turbulence generally affects the mixing characteristics of the buoyant jet, and the extent of the influence depends on the characteristics of both the jet discharge and ambient. Previous studies focused on the experimental investigation of the problem (for pure jets or plumes), but the findings were difficult to generalize because suitable scales for normalization of results were not known. A model to predict the buoyant jet mixing in the presence of background turbulence, which is essential in many applications, is also hitherto not available even for a background of homogeneous and isotropic turbulence (HIT). We carried out experimental and theoretical investigations of a buoyant jet discharging into background HIT. Buoyant jets were designed to be in the range of $1&lt;z/l_{M}&lt;5$, where $l_{M}=M_{o}^{3/4}/F_{o}^{1/2}$ is the momentum length scale, with $z/l_{M}&lt;\sim 1$ and $z/l_{M}&gt;\sim 6$ representing the asymptotic cases of pure jets and plumes, respectively. The background turbulence was generated using a random synthetic jet array, which produced a region of approximately isotropic and homogeneous field of turbulence to be used in the experiments. The velocity scale of the jet was initially much higher, and the length scale smaller, than that of the background turbulence, which is typical in most applications. Comprehensive measurements of the buoyant jet mixing characteristics were performed up to the distance where jet breakup occurred. Based on the experimental findings, a critical length scale $l_{c}$ was identified to be an appropriate normalizing scale. The momentum flux of the buoyant jet in background HIT was found to be conserved only if the second-order turbulence statistics of the jet were accounted for. A general integral jet model including the background HIT was then proposed based on the conservation of mass (using the entrainment assumption), total momentum and buoyancy fluxes, and the decay function of the jet mean momentum downstream. Predictions of jet mixing characteristics from the new model were compared with experimental observation, and found to be generally in agreement with each other.

Research on Jet Current Field Characteristic under Waves by Numerical Modelling in Flowing Ambient Fluid

A variable density anisotropic turbulent buoyant jet model is applied for simulating the current field under waves. The numerical simulation results show the present model is efficient to describe the construction characteristic of current field. This model could be an efficient tool for sewage treatment by deep sea discharge.

Estimation of Near-Field and Far-Field Dilutions for Site Selection of Effluent Outfall in a Coastal Region—A Case Study

ABSTRACT Naidu, V.S., 2013. Estimation of near-field and far-field dilutions for site selection of effluent outfall in a coastal region—a case study. Site selection for release of industrial effluents is of prime concern for maintaining the quality of the marine environment. In this study, an attempt has been made to establish the prevailing ecological conditions and to suggest the suitable location for discharge of the effluents into the sea by using near-field and far-field models. Near-field dilutions were calculated using a buoyant jet model, whereas far-field dilutions were estimated using a two-dimensional numerical model. As a case study, the location of outfall is to be suggested to Vapi Waste and Effluent Management Company Ltd. (VWEMCL) for the release of treated effluents. At present, VWEMCL is discharging effluents upstream of the Damanganga estuary. As a result, the entire Damanganga estuary has poor water quality. Field studies conducted in 2009 suggested that the Damanganga estuarine segmen...

Numerical Simulation of Sewage Treatment by Deep Sea Discharge in Flowing Ambient Fluid

Sewage deep sea discharge is used in nearshore district, which has a characteristic of jet. In this paper, anisotropic turbulent buoyant jet model is applied for simulating the current field of jet and the distribution of pollutant dilution. The scale of recirculation zone is very important parameter for sewage dilution, which is simulated in this paper.

Optimal Coupled Inversion for Jet Parameters in Flowing Ambient Fluid

A new multi-parameter optimal inversion method for jet ratio and jet angle is established by coupling data-driven model theory with variable density anisotropic turbulent buoyant jet model in this paper. In this method, firstly the multi-parameter matching cases of jet ratio and jet angle are computed by the jet model, and the solution space of internal observation site in the computation waters is constructed by numerical simulation results. Secondly, the nonlinear relationship between state variables (dilution degree) and control variables (model multi-parameter) is established by data-driven model theory. Finally the optimal solution is obtained by inputting the needed dilution degree to the relationship. The numerical results show that multi-parameter optimal coupled inversion method is efficient for the optimal jet parameters and has advantages of jet water mixing with environment water.

Dynamic interaction of multiple buoyant jets

AbstractAn array of closely spaced round buoyant jets interact dynamically due to the pressure field induced by jet entrainment. Mutual jet attraction can result in a significant change in jet trajectories. Jet merging also leads to overlapping of the passive scalar fields associated with the individual jets, resulting in mixing characteristics that are drastically different from those of an independent free jet. A general semi-analytical model for the dynamic interaction of multiple buoyant jets in stagnant ambient conditions is proposed. The external irrotational flow field induced by the buoyant jets is computed by a distribution of point sinks with strength equal to the entrainment per unit length along the unknown jet trajectories and accounting for boundary effects. The buoyant jet trajectories are then determined by an iterative solution of an integral buoyant jet model by tracking the changes in the external entrainment flow and dynamic pressure fields. The velocity and concentration fields of the jet group are obtained by momentum or kinetic energy superposition for merged jets and plumes, respectively. The modelling approach is supported by numerical solution of the Reynolds-averaged Navier–Stokes equations. The model shows that jet merging and mixing can be significantly affected by jet interactions. Model predictions of the multiple jet trajectories, merging height, as well as the centreline velocity and concentration of the buoyant jet group are in good agreement with experimental data for: (i) a clustered momentum jet group; (ii) a turbulent plume pair; and (iii) a rosette buoyant jet group. Dynamic interactions between a jet group are shown to decrease with the addition of an ambient cross-flow.

Development and application of 3D numerical model THREETOX to the prediction of cooling water transport and mixing in the inland and coastal waters

AbstractA modelling system—THREETOX—has been developed to simulate the transport and mixing of cooling water in both freshwater and marine environment. A 3D hydrostatic free‐surface model describes the heat dispersion in the far‐field, whereas an integral buoyant jet model coupled with a far‐field model is applied to the near‐field. The equations of hydrodynamics of the far‐field model are completed by equations for heat and salt transport, and by the k − ε turbulence model. Special attention is paid to the parameterization of heat fluxes between water and atmosphere and between water and bottom sediments. Wetting and drying (WAD) processes were built into the model to describe areas where tide and floods play a dominant role. The model was enhanced by processes describing the effects of ship traffic on the dispersion of the discharged heat in stagnant canals. The sigma coordinate in the upper layer can be combined in the lower layer with a second sigma coordinate system or with a z coordinate system. An orthogonal curvilinear horizontal grid with two‐way nesting capabilities has been used to describe the area of interest accurately. A high order advection scheme has been applied in the model. Several examples of the application and validation of the THREETOX model are presented. Studies were performed on the dispersion of cooling water, discharged by various power plants in the Netherlands located at different types of aquatic systems, varying from rivers, canals to tidal river reaches. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Vertical thermal-buoyant jets

A study of plane thermal-buoyant jets is presented. Experiments were conducted in water, and the results are compared with two integral models, namely a buoyant jet model and a thermal jet model. In the buoyant jet model the equation of state is linear, while in the thermal jet model the equation of state is nonlinear. It is concluded that the buoyant jet model does not adequately predict the behaviour of thermal buoyant jets in a cold water environment. For such flows it is necessary to use the actual equation of state for water.

Generalized Lagrangian Model for Buoyant Jets in Current

A general Lagrangian jet model formulation is presented for an inclined buoyant jet in a current, with a three‐dimensional trajectory. The shear‐induced entrainment is computed as a function of the local densimetric Froude number and jet orientation, while the forced entrainment is taken as the ambient flow intercepted by the “windward” side of the buoyant jet. Model predictions are compared with both trajectory and tracer concentration data for a wide range of discharge and ambient flow conditions: horizontal buoyant jets in a coflow; vertical jets, oblique jets, and dense plumes in a cross flow; buoyant jets in a stagnant uniform or stratified fluid; and a horizontal buoyant jet in a perpendicular cross flow. The model is also consistent with the concept of asymptotic flow regimes, and reproduces the correct behavior in both the near and far field of a vertical momentum of buoyancy‐dominated jet in a cross flow. The connection of the model with traditional integral jet models is also discussed.