Turbulent Jets

The study of quasi-two-dimensional turbulent jets is relevant to chemical reactors, the coking process in oil refinement, as well as rivers flowing into lakes or oceans. In the event of a spillage of pollutants into a river, it is critical to understand how these agents disperse with the flow in order to assess damage to the environment. For such flows, characteristic streamwise and cross-stream dimensions can be much larger than the fluid-layer thickness, and so the flow develops in a confined environment. When the distance away from the discharge location is larger than ten times the fluidlayer thickness, the flow is referred to as a quasi-two-dimensional jet. From experimental observations using dyed jets and particle image velocimetry, we find that the structure of a quasi-two-dimensional jet consists of a high-speed meandering core with large counter-rotating eddies developing on alternate sides of the core. The core and eddy structure is self-similar with distance from the discharge location. The Gaussianity of the cross-stream distribution of the time-averaged velocity is due, in part, to the sinuous instability of the core.

In this paper, computations of transient, incompressible, turbulent, plane jets using the discrete lattice BGK Boltzmann equation are reported. Á priori derivation of the discrete lattice BGK Boltzmann equation with a spatially and temporally dependent relaxation time parameter, which is used to represent the averaged flow field, from its corresponding continuous form is given. The averaged behavior of the turbulence field is represented by the standard k–∊ turbulence model and computed using a finite-volume scheme on nonuniform grids. Computed results are compared with analytical solutions, experimental data and results of other computational methods. Satisfactory agreement is shown.

In this paper, computations of transient, incompressible, turbulent, plane jets using the discrete lattice BGK Boltzmann equation are reported. Á priori derivation of the discrete lattice BGK Boltzmann equation with a spatially and temporally dependent relaxation time parameter, which is used to represent the averaged flow field, from its corresponding continuous form is given. The averaged behavior of the turbulence field is represented by the standard k–∊ turbulence model and computed using a finite-volume scheme on nonuniform grids. Computed results are compared with analytical solutions, experimental data and results of other computational methods. Satisfactory agreement is shown.

The presem investigation reports on the near field behavior of gas jets in a long confinement and points out the differences between this type of jet flow and those of free jets and jets in a short confinement. The jet, with a diameter of 8.73 mm, is aligned concentrically with a tube of 125 mm diameter; thus giving a confinement area ratio of ~ 205. The arrangement forms part of the test section of an open-jet wind tunnel and this gives a confinement length-to-jet diameter ratio of ~ 1,700. Experiments are carried out with Carbon dioxide, air and helium/air jets at different jet velocities. Mean velocity and turbulence measurements are made of the jet near field using a one-color, one-component laser doppler velo-Cimeter operating in the forward scatter mode. In addition, the turbulent shear field of an air jet is examined in more detail using hot-wire anemometers. In view of the long confinement, the presence of the jet is not being felt immediately at the tunnel exit. Consequently, the air column inside the tunnel is first compressed by the jet and then s!owly pushed out of the tunnel. This behavior causes the jet to spread rapidly and to decay quickly. As a result, an equilibrium turbulence field is established in the first two diameters of the jet. This equilibrium field bears striking similarity to that found in self-preserving, turbulent free jets and jets in short confinement and is independent of jet fluid densities and velocities. In terms of these characteristics, the near field of jets in a long confinement is very different from that found in free jets and jets in short confinements.

The presem investigation reports on the near field behavior of gas jets in a long confinement and points out the differences between this type of jet flow and those of free jets and jets in a short confinement. The jet, with a diameter of 8.73 mm, is aligned concentrically with a tube of 125 mm diameter; thus giving a confinement area ratio of ~ 205. The arrangement forms part of the test section of an open-jet wind tunnel and this gives a confinement length-to-jet diameter ratio of ~ 1,700. Experiments are carried out with Carbon dioxide, air and helium/air jets at different jet velocities. Mean velocity and turbulence measurements are made of the jet near field using a one-color, one-component laser doppler velo-Cimeter operating in the forward scatter mode. In addition, the turbulent shear field of an air jet is examined in more detail using hot-wire anemometers. In view of the long confinement, the presence of the jet is not being felt immediately at the tunnel exit. Consequently, the air column inside the tunnel is first compressed by the jet and then s!owly pushed out of the tunnel. This behavior causes the jet to spread rapidly and to decay quickly. As a result, an equilibrium turbulence field is established in the first two diameters of the jet. This equilibrium field bears striking similarity to that found in self-preserving, turbulent free jets and jets in short confinement and is independent of jet fluid densities and velocities. In terms of these characteristics, the near field of jets in a long confinement is very different from that found in free jets and jets in short confinements.

The modeling of flow induced by submerged sewer system was carried out within laborarory physical experiment. Results of experiments perfomed at two expeimental facilities (Large Termostratified Tank LTSB (20*4*2 m) and small ltank (1.2*0.5*0.5 m) with saline stratification) are presented. The theoretical model of was verified within the series of experiments in saline pycnocline-type stratification in wide range of parameters. The conditions of scaling modeling were determined on the basis of this model, and laboratory scale modeling with geometrical scale 1:27 was perfomed in LTSB. Excitation of intencive temperature oscillations in the picnocline was observed. They were interpreted as self-sustained oscillations of the buoayant plume.

The presem investigation reports on the near field behavior of gas jets in a long confinement and points out the differences between this type of jet flow and those of free jets and jets in a short confinement. The jet, with a diameter of 8.73 mm, is aligned concentrically with a tube of 125 mm diameter; thus giving a confinement area ratio of ~ 205. The arrangement forms part of the test section of an open-jet wind tunnel and this gives a confinement length-to-jet diameter ratio of ~ 1,700. Experiments are carried out with Carbon dioxide, air and helium/air jets at different jet velocities. Mean velocity and turbulence measurements are made of the jet near field using a one-color, one-component laser doppler velo-Cimeter operating in the forward scatter mode. In addition, the turbulent shear field of an air jet is examined in more detail using hot-wire anemometers. In view of the long confinement, the presence of the jet is not being felt immediately at the tunnel exit. Consequently, the air column inside the tunnel is first compressed by the jet and then s!owly pushed out of the tunnel. This behavior causes the jet to spread rapidly and to decay quickly. As a result, an equilibrium turbulence field is established in the first two diameters of the jet. This equilibrium field bears striking similarity to that found in self-preserving, turbulent free jets and jets in short confinement and is independent of jet fluid densities and velocities. In terms of these characteristics, the near field of jets in a long confinement is very different from that found in free jets and jets in short confinements.

This paper focuses on the effects of a space-time dependent periodic stirring of a moderately turbulent planar coflow jet configuration. The baseline flow is agitated in time and in space by small-scale turbulent perturbations in combination with large-scale modulation imposed at the inflow plane of a rectangular domain of size L × L × 2L in the x, y and z directions respectively. The prescribed large-scale modulation is characterized by a single modulation frequency ω and modulation wave-number, K. A parametric study at different modulation frequencies and wave-numbers is performed. We evaluate the system response to the external agitation in terms of key dynamic properties of the flow, e.g., the total kinetic energy E T , the global averaged dissipation rate and additional flow mixing properties. For low modulation frequencies, e.g., = 0.5 , 0 where ω 0 is the large scaleturn over frequency, = U D / , 0 1 with U 1 and D being relevant velocity and length scales, and at given wavenumber K, we observe that E T follows the imposed oscillation with a periodic amplitude response that is sustained at locations further from the inflow plane, whereas for higher frequencies, the response amplitude rapidly decays. Results of the global dissipation rate show the development of a definite maximum value of the response amplitude at frequencies on the order of ω 0 for any modulation wave-number K. To investigate in more detail the effects of modulated turbulence on the jet mixing properties, a passive scalar was injected at the inflow plane. The spreading of the scalar surface in the agitated jet was monitored for a wide range of modulation frequencies. In general, results show enhanced mixing efficiency when the main jet is modulated at frequencies near ω 0 and low K values.

INERIS has set up large-scale fully instrumented experiments to study the formation of flammable clouds resulting from a finite duration spillage of hydrogen in a quiescent room (80 m 3 chamber). Concentration, temperature and mass flow measurements were monitored during the release period and several hours after. Experiments were carried out for mass flow rates ranging from 0,2 g/s to 1 g/s. The instrumentation allowed the observation and quantification of rich hydrogen layers stratification effects. This paper presents both the experimental facility and the test results. These experimental results can be used to assess and benchmark CFD tools capabilities.

In this paper, computations of transient, incompressible, turbulent, plane jets using the discrete lattice BGK Boltzmann equation are reported. Á priori derivation of the discrete lattice BGK Boltzmann equation with a spatially and temporally dependent relaxation time parameter, which is used to represent the averaged flow field, from its corresponding continuous form is given. The averaged behavior of the turbulence field is represented by the standard k–∊ turbulence model and computed using a finite-volume scheme on nonuniform grids. Computed results are compared with analytical solutions, experimental data and results of other computational methods. Satisfactory agreement is shown.

A plane, turbulent, nonbuoyant, vertical jet in shallow water is simulated numerically using a three-dimensional computation model employing standard k-ε and renormalized group k-ε turbulent closure schemes. Existing data of mean and turbulent flow quantities, measured using laser Doppler velocimeter, are used to assess the two turbulent closure schemes. Comparisons between the measured and simulated flow field data are made in the free jet region, within the zone of surface impingement, and in the zone of horizontal jets at the surface. The results show that the standard k-ε scheme performs equally well and in some areas better than the more complicated renormalized group k-ε scheme in simulating the mean and turbulent flow quantities in this case.

In this paper, computations of transient, incompressible, turbulent, plane jets using the discrete lattice BGK Boltzmann equation are reported. Á priori derivation of the discrete lattice BGK Boltzmann equation with a spatially and temporally dependent relaxation time parameter, which is used to represent the averaged flow field, from its corresponding continuous form is given. The averaged behavior of the turbulence field is represented by the standard k–∊ turbulence model and computed using a finite-volume scheme on nonuniform grids. Computed results are compared with analytical solutions, experimental data and results of other computational methods. Satisfactory agreement is shown.

The knowledge of density current behaviours as a result of two or more fluids of different densities interacting is of particular importance in many practical applications. Within the field of hydraulic engineering, examples include buoyant effluent discharges from desalination plants, advancements of saline water under freshwater in estuaries, and flows occurring when a gate is removed at the outflow/inflow of a river. The main goal of this study is to improve the understanding of the mixing patterns of density currents as well as their related numerical simulation. In this study, first, an advanced numerical solver for 2D variable-density shallow water equations is developed and validated where both well balanced and positivity preserving properties are achieved over an unstructured grid. The improved numerical scheme is flexible, and accounts for flooding over irregular bed topographies by using a triangular grid. Second, a numerical study of two-layer stratified flows over an is...

The present paper investigates numerically two-and threedimensional incompressible turbulent flows in a 180° curved diffuser of rectangular cross section by using the commercial code Fluent. In the case of 2-D turbulent flow, the predicted numerical results have been compared with available experimental results. The turbulent flow in the curved diffuser has been analyzed numerically using five turbulence models: the standard k-model, the Renormalization-group (RNG) kmodel, the Realizable k-model, the k-model, and the Reynolds stress model (RSM). All employed turbulent models predicted the main features of the flow but a later separation position than the experiment is expected. More advanced turbulence model such as the Reynolds-stress model and RNG k-model have more reliable numerical results especially at separation zone. However, the computations take longer time. The reattachment lengths predicted by all models are over predicted.

A plane, turbulent, nonbuoyant, vertical jet in shallow water is simulated numerically using a three-dimensional computation model employing standard and renormalized group turbulent closure schemes. Existing data of mean and turbulent flow quantities, measured using laser Doppler velocimeter, are used to assess the two turbulent closure schemes. Comparisons between the measured and simulated flow field data are made in the free jet region, within the zone of surface impingement, and in the zone of horizontal jets at the surface. The results show that the standard scheme performs equally well and in some areas better than the more complicated renormalized group scheme in simulating the mean and turbulent flow quantities in this case.

The present paper investigates numerically two-and threedimensional incompressible turbulent flows in a 180° curved diffuser of rectangular cross section by using the commercial code Fluent. In the case of 2-D turbulent flow, the predicted numerical results have been compared with available experimental results. The turbulent flow in the curved diffuser has been analyzed numerically using five turbulence models: the standard k-model, the Renormalization-group (RNG) kmodel, the Realizable k-model, the k-model, and the Reynolds stress model (RSM). All employed turbulent models predicted the main features of the flow but a later separation position than the experiment is expected. More advanced turbulence model such as the Reynolds-stress model and RNG k-model have more reliable numerical results especially at separation zone. However, the computations take longer time. The reattachment lengths predicted by all models are over predicted.

The mean velocity and turbulent intensity of an axisymmetric jet exiting from a round orifice located some distance above a solid surface were measured using a hot-wire anemometer. The effect of the presence of the ground plane was to flatten the circular shape of the isopleths, and due to Coanda effect the locations of the maximum velocity at the cross sections of the jet were found to be deflected to approach the ground. Furthermore the shape of each isopleth was found to be significantly  flattened from its circular shape if the ground wasn't there.

The velocity and temperature fields were measured below two parallel, rectangular air nozzles. The nozzles were closely spaced, and each nozzle had an l/w (length to width ratio) ranging from 55 to 170. The jets intersected at a 60°angle. Operating temperatures ranged from ambient to 321°C. Measurements demonstrated that the temperature fields were analogous to the velocity fields. Hence, similar correlations were developed to describe either type of field. IE970145N X Abstract published in Advance ACS Abstracts, June 15, 1997.

In this study, plane and circular turbulent non-buoyant jets are simulated numerically using a three-dimensional computational model. The aim of the study is to evaluate the accuracy of turbulent closure schemes employed in three-dimensional models. In particular, standard k-epsilon and renormalized group k-epsilon schemes with standard coefficients are evaluated. The modeled jets are deeply submerged, that is the impact of free surface and solid boundaries on jets are eliminated. The accuracy of the turbulent schemes is assessed by analyzing the decay of centerline velocity, jet growth rates, similarity of longitudinal and vertical velocity profiles, and turbulent kinetic energy profiles. The results from the two turbulent closure schemes are compared with accepted experimental and theoretical studies to determine their accuracy. It is found that the k-epsilon scheme with standard coefficient performs equally well and in some cases better than the renormalized group k-epsilon scheme. Finally, the model is applied to analyze flow pattern in the Sampit River, South Caroline, USA, resulting from stormwater discharge in a recreational area. Various inlet designs are investigated and box inlet is found to provide a practical means of localizing high surface currents.

Keywords: computational modeling; turbulent jets; storm water discharge; turbulent closure schemes