Buoyant Jets In Crossflow Research Articles

Surface Currents Effect in the Explicit Algebraic Reynolds Stress Turbulence Model for Simulation of Lateral Buoyant Jets in Cross-Flow

Surface Currents Effect in the Explicit Algebraic Reynolds Stress Turbulence Model for Simulation of Lateral Buoyant Jets in Cross-Flow

Buoyant Jets in Cross-Flows: Review, Developments, and Applications

Significant environmental effects from the use of marine outfall discharges have led to increased efforts by both regulatory bodies and research groups to minimize the negative impacts of discharges on the receiving water bodies. Understanding the characteristics of discharges under conditions representative of marine environments can enhance the management of discharges and mitigate the adverse impacts to marine biota. Thus, special attention should be given to ambient cross-flow effects on the mixing behaviors of jet discharges. A buoyant jet in cross-flow has different practical applications such as film cooling and dilution, and provide a higher mixing capability in comparison with free jets or discharges into stationary environments. The main reason for this is believed to be the existence of various complicated vortical structures including a counter-rotating vortex pair as the jet expands downstream. Although tremendous research efforts have been devoted to buoyant jets issuing into cross-flows over the past five decades, the mixing process of an effluent at the discharge point is not yet well understood because of the highly complex fluid interactions and dispersion patterns involved. Therefore, there is a need for a deeper understanding of buoyant jets in cross-flows in order to obtain better predictive methods and more accurate design guidelines. The main aims of this study were (i) to establish the background behind the subject of buoyant jets in cross-flows including the flow structures resulting from the interaction of jets and cross-flows and the impacts of current on mixing and transport behavior; (ii) to present a summary of relevant experimental and numerical research efforts; and finally, (iii) to identify and discuss research gaps and future research directions.

Experimental study of surface buoyant jets in crossflow

The dispersion of surface jets in crossflows such as rivers or channels can cause critical environmental problems in the form of chemical or thermal pollution of these water bodies. The turbulent flow structures occurring in such crossflows play an important role in the mixing of surface jets with the surrounding water bodies. In this study, experimental measurements of the time history of the 3-D velocity field were conducted to better understand the flow structure of surface jets in crossflow conditions. Stereoscopic Particle Image Velocimetry was used to measure the instantaneous spatial and temporal velocity distribution downstream of the jet’s discharge point. In addition to the mean velocity distribution, turbulent flow characteristics such as the turbulent kinetic energy ( $$k$$ ), turbulent kinetic energy dissipation rate ( $$\epsilon$$ ), and turbulent eddy viscosity ( $$\nu_{t}$$ ) were calculated. The formation and evolution of a vortex in the surface jet’s flow structure was detected over the measurement zone. The vortex in the surface jets in crossflow resembled to half of the vortices in a counter-rotating vortex pair (CVP) of submerged jets in crossflows. It can be inferred that the water surface performed like a plane of symmetry.

Turbulent Interaction of a Buoyant Jet with Cross-Flow

AbstractThis 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 (kn) 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 kn=0 and β=0.7; those values result in better predictions than when using the advised values—namely, kn=1, 0.34<β<0.62. Cross contours for concentration (C/Cmax) and f...

Testing an Improved Artificial Viscosity Advection Scheme to Minimise Wiggles in Large Eddy Simulation of Buoyant Jet in Crossflow

Obtaining accurate and wiggle free Large Eddy Simulation (LES) results of high Re configurations with obstacles is a challenge, especially when the resolution is moderate. This study focusses on LES of buoyant jet in crossflow (JICF). The zone in front of the jet is sensitive for wiggle formation because the jet acts as an obstacle. Only 10 grid cells over the diameter of the jet at outflow are used in order to be able to simulate very large mixing areas with limited CPU power. The resolution increases rapidly to 30–50 cells over the diameter of the bend over jet further downstream. This study tests an artificial viscosity advection scheme with sixth order dissipation, called AV6, which dissipates wiggles adequately with almost no dissipation on physical relevant scales. This desirable behaviour is demonstrated by a Fourier analysis of the Advection-Diffusion equation and turbulent flow simulations. AV6 is a mix of, and improvement over, the artificial viscosity scheme of Jameson et al. (1981) with fourth order dissipation, here called AV4, and a fifth order upwind scheme (UPW5) of Wicker and Skamarock (Mon Weather Rev 130:2088, 2002). AV6 is a robust, simple and easy to implement advection scheme and the total computational time of a simulation with AV6 is only a few percent more than with the second order central scheme (CDS2). Three realistic turbulent flow problems, relevant for buoyant JICF, are used to compare the performance of AV6 with CDS2, AV4 and UPW5 with each other and with experiments. Different grid resolutions and sub-grid scale models are used. The three test cases are a non-buoyant JICF, a buoyant jet in weak coflow, and a buoyant JICF. Of all tested advection schemes, AV6 produces best results and is preferred for LES of buoyant JICF.

Effect of ambient stratification on buoyant jets in cross-flow

Effect of ambient stratification on buoyant jets in cross-flow

Effect of ambient stratification on buoyant jets in cross-flow

Effect of ambient stratification on buoyant jets in cross-flow

General Integral Formulation of Turbulent Buoyant Jets in Cross-Flow

The turbulent buoyant jet in a nonuniform cross-flow is formulated using a general integral method. The integral equations for the turbulent motion through the jet cross section are derived for a fixed control volume and expressed in vector form. In contrast to previous work, the new formulation does not require the a priori assumption of a velocity and concentration distribution. Coupled with a Lagrangian jet spreading hypothesis and the inclusion of added mass effect, the model is shown to predict correctly the properties of the asymptotic flow regimes in both the near field (straight jet and plume) and the far field (advected line puff and thermal). Predictions of the path-averaged jet properties are shown to be consistently supported by experimental data on visual trajectory and jet width, and centerline minimum dilution. The relation between the present formulation and previous Lagrangian/Eulerian models is also discussed.

Effect of Ambient Stratification on Buoyant Jets in Cross-Flow

A numerical technique for integrating the fully elliptic Reynolds-averaged Navier-Stokes and diffusion equations has been used to investigate the effect of ambient density stratification on the flow characteristics of a vertical force plume in a cross-flow of a stably linear stratified environment. A two-equation \ik-ϵ turbulence model is employed to simulate the turbulent transport quantities and to close the solving problem. Some basic flow features and a structure for the interaction of the buoyant jets with a density-stratified cross-flow are obtained. The results show that the ambient stratification tends to inhibit the flow development of the buoyant source and to encourage the formation of secondary and third vortex pairs in the jet cross section as a plume flowing downstream. It then results in causing the jet-flow oscillation from its maximum height-of-rise.

Flow of Surface Buoyant Jet in Cross Flow

A laboratory study is conducted to determine the flow parameters of a rectangular surface jet discharging normally onto a cross flow. The Reynolds numbers of the buoyant jet and the cross flow are 11×104 and 7.4×104, respectively, with a densimetric Froude number of 1.7 and a ratio of ambient velocity to jet velocity of 0.9. Vertical and horizontal isotherms are determined, and it is found that the jet axis is strongly depth‐dependent. Profiles of the mean velocity and the temperature turbulence intensity are measured at various downstream sections. Lateral profiles of the temperature flatness factor, skewness factor, temperature length scale, and the warm water flux are measured at one cross section. The transport of warm water by large‐scale structure is discussed.

Initial Dilution of Horizontal Jet in Crossflow

Available data on the initial dilution of a horizontal round buoyant jet in a perpendicular crossflow are successfully interpreted using length scales and mathematical models. The database consists of in situ measurements of surface dilution in the sewage boil at a number of sea outfalls in the United Kingdom, as well as limited laboratory experimental data. Simple equations for the prediction of minimum initial dilution in an ambient current are well‐supported by the collective data. The dilution constants obtained are comparable to but greater than those derived from previous laboratory experiments of a vertical negatively buoyant jet in a crossflow. A correlation for the downstream location of minimum dilution is also provided. The results reported herein can be readily used in outfall design.

Vortex Dynamics and Bifurcation of Buoyant Jets in Crossflow

A model is developed which predicts the integral behavior of buoyant or nonbuoyant jets in crossflow with the superimposed effect of the counterrotating internal vortex structure which exists in a plane normal to the jet trajectory. Despite some real fluid effects, such as finite vortex core size and turbulent growth, classical irrotational vortex pair theory is an adequate first-order model for the motions induced in the surrounding fluid. If these outside motions are constrained—either by a fluid boundary or by the effects of density stratification—then a repulsive force mechanism is created. This force leads to bifurcation of the bent-over jet into two separate elements with undiluted fluid in between. The theory shows excellent agreement with available experimental data for homogenous crossflow of finite depth. An application to hypothetical cases of stratified crossflow predicts different environmental conditions under which jet bifurcation can occur.

L. N. Fan's Data on Buoyant Jets in Crossflow

Buoyant Jets in a crossflow can be described in a simplified manner by means of a ..line impulse model... The model was originally introduced by Priestly and Scorer and has been generalized by the writer to more complex flow situations. In this note, this simplified approach is used to reanalyze the comprehensive and well documented set of data by L. N. Fan.