Numerical Simulation of Turbulent Jets (original) (raw)
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Simulation of vertical plane turbulent jet in shallow water
Advances in Civil Engineering, 2011
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.
Numerical Simulation of Free Surface in the Case of Plane Turbulent Wall Jets in Shallow Tailwater
Wall-jet flow is an important flow field in hydraulic engineering, and its applications include flow from the bottom outlet of dams and sluice gates. In this paper, the plane turbulent wall jet in shallow tailwater is simulated by solving the Reynolds Averaged Navier-Stokes equations using the standard k turbulence closure model. This study aims to explore the ability of a time splitting method on a non-staggered grid in curvilinear coordinates for simulation of two-dimensional (2D) plane turbulent wall jets with finite tailwater depth. In the developed model, the kinematic free-surface boundary condition is solved simultaneously with the momentum and continuity equations, so that the water surface elevation can be obtained along with the velocity and pressure fields as part of the solution. 2D simulations are carried out for plane turbulent wall jets free surface in shallow tailwater. The comparison undertaken between numerical results and experimental measurements show that the numerical model can capture the velocity field and the drop in the water surface elevation at the gate with reasonable accuracy.
Journal of Fluid Mechanics, 2009
Jets arising from rivers, streams and tidal flows entering still waters differ from most experimental studies of jets both in aspect ratio and in the presence of a solid bottom boundary and an upper free surface. Despite these differences, the applicability of experimental jet studies to these systems remains largely untested by either field or realistically scaled experimental studies. Here we present experimental results for a wall-bounded plane jet scaled to jets created by flow discharging into floodplain lakes. A characteristic feature of both our prototype and experimental jets is the presence of large-scale meandering turbulent structures that span the width of the jets. In our experimental jets, we observe self-similarity in the distribution of mean streamwise velocities by a distance of six channel widths downstream of the jet outlet. After a distance of nine channel widths the velocity decay and the spreading rates largely agree with prior experimental results for plane jets. The magnitudes and distributions of the cross-stream velocity and lateral shear stresses approach self-preserving conditions in the upper half of the flow, but decrease in magnitude, and deviate from self-preserving distributions with proximity to the bed. The presence of the meandering structure has little influence on the mean structure of the jet, but dominates the jet turbulence. A comparison of turbulence analysed at time scales both greater than and less than the period of the meandering structure indicates that these structures increase turbulence intensities by 3-5 times, and produce lateral shear stresses and momentum diffusivities that are one and two orders of magnitude greater, respectively, than turbulence generated by bed friction alone.
A real problem when trying to develop a numerical model reproducing the flow through an orifice is the choice of a correct value for the turbulence intensity at the inlet of the numerical domain in order to obtain at the exit plane of the jet the same values of the turbulence intensity as in the experimental evaluation. There are few indications in the literature concerning this issue, and the imposed boundary conditions are usually taken into consideration by usage without any physical fundament. In this article we tried to check the influence of the variation of the inlet turbulence intensity on the jet flow behavior. This article is focusing only on the near exit region of the jet. Five values of the inlet turbulence intensity Tu were imposed at the inlet of the computational domain, from 1.5% to 30%. One of these values, Tu= 2% was the one measured with a hot wire anemometer at the jet exit plane, and another one Tu= 8.8% was issued from the recommendation of Jaramillo [1]. The choice of the mesh-grid and of the turbulence model which was the SST k-ω model were previously established [2]. We found that in the initial region of the jet flow, the mean streamwise velocity profiles and the volumetric flow rate do not seem to be sensitive at all at the variation of the inlet turbulence intensity. On the opposite, for the vorticity and the turbulent kinetic energy (TKE) distributions we found a difference between the maximum values as high as 30%. The closest values to the experimental case were found for the lowest value of Tu, on the same order of magnitude as the measurement at the exit plane of the jet flow. Mean streamwise velocity is not affected by these differences of the TKE distributions. Contrary, the transverse field is modified as it was displayed by the vorticity distributions. This observation allows us to predict a possible modification of the entire mean flow field in the far region of the jet flow.
Numerical simulation of high-speed turbulent water jets in air
Journal of Hydraulic Research, 2010
Numerical simulation of high-speed turbulent water jets in air and its validation with experimental data has not been reported in the literature. It is therefore aimed to simulate the physics of these high-speed water jets and compare the results with the existing experimental works. High-speed water jets diffuse in the surrounding atmosphere by the processes of mass and momentum transfer. Air is entrained into the jet stream and the entire process contributes to jet spreading and subsequent pressure decay. Hence the physical problem is in the category of multiphase flows, for which mass and momentum transfer is to be determined to simulate the problem. Using the Eulerian multiphase and the k-e turbulence models, plus a novel numerical model for mass and momentum transfer, the simulation was achieved. The results reasonably predict the flow physics of high-speed water jets in air.
Large eddy simulation of buoyant jet in shallow water
2016
Large eddy simulation of buoyant jet in shallow water Akihiko Nakayama, Jeremy D. Bricker and Zafarullah Nizamani Department of Environmental Engineering, Universiti Tunku Abdul Rahman akihiko@utar.edu.my Abstract A numerical method of predicting the turbulent mixing process of disposed water from an outfall in a shallow coastal water is described. The momentum equations for the sea water mixed with treated water of small salinity and warmer temperature are solved numerically together with the equation of the concentration of the treated water. The basic method is a Large Eddy Simulation (LES) formulated on a fixed rectangular grid where boundaries are approximated by Immersed Boundary (IB) method. The sub-grid effects of the unresolved fluctuations of velocity and the concentration fields are expressed by the eddy viscosity and eddy diffusivity with the Smagorinsky model. The method is verified with an experiment and RANS calculation of the buoyant wall jet issuing on a solid surfa...
Numerical Heat Transfer, Part A: Applications, 2016
The evolution of turbulent rectangular submerged free jets has been investigated numerically with a twodimensional approach, [1], by using the Large Eddy Simulations (LES) at several Reynolds numbers. The average numerical results confirmed the presence of the undisturbed region of flow, URF, located between the slot exit and the beginning of the potential core region, PCR, previously observed experimentally at the University of Rome "Tor Vergata". The two-dimensional study, [1], carried out under the conditions previously investigated in the literature, showed that the URF has a self-similar behavior, and proposed a new law for the evolution of the momentum. The present paper extends the Large Eddy Simulations (LES) to threedimensional rectangular submerged free jets, showing that the self-similar behavior of URF is present also in the three-dimensional numerical simulations, as well as in the PCR and in the fully developed region, FDR.
Prediction of turbulent, axisymmetric, dense jets discharged to quiescent ambients
Mathematical and Computer Modelling, 1989
The analysis of dense jets is of interest with regard to environmental applications, especially in the design and evaluation of submerged, offshore outfalls from desalination plants. In this paper, the governing conservation equations of mass, momentum, energy and salinity, derived in a curvilinear coordinate system, are solved by an explicit finite-difference method. The influence of temperature and salinity on density of the jet and ambient fluid are incorporated using an equation of state. Turbulent shear stress, heat flux and mass flux terms appearing in the governing equations are evaluated using simple algebraic expressions for the eddy diffusivities that account for effects on mixing of buoyancy and intermittent turbulence near the edge of the jet. The formulation is parabolic in character, allowing the solution to be marched in the streamwise direction starting with initial distributions of velocity, temperature, salinity and discharge orientation. Cases investigated are the dense jet discharging vertically, horizontally and at various angles to the horizontal into quiescent, uniform or stratified ambient. Predictions are compared with available experimental data for a wide range of Froude numbers.
Simulation of Local Scour Caused by Submerged Horizontal Jets with FLOW-3D Numerical Model
Desert, 2015
One of the most concerning issues for researchers is to predict the shape and dimensions of the scour pit nearhydraulic structures such as the base of bridges, weirs, valves and stilling basins due to both financial and humanhazards induced by destruction of the structure. As the scour issue has its own complexity in relation to themultiplicity of effecting factors on it, in this study therefore, the results of laboratory analysis of local scour due tosubmerged horizontal jets were compared with numerical simulation results from Flow-3D three-dimensional modelto test the potency of the numerical model. As a result, the model is proposed in place of the experimental modelwhich has its own drawbacks and high costs. In this study, we measure maximum scour depth in relative equilibriumin 2 states and 6 test modes with different valve openings and tail water depth per different discharges. Comparisonof the results indicates about 11% error for Flow-3D numerical model in relation to the e...
International Journal of Heat and Fluid Flow, 2016
In this paper, the behavior and turbulence structure of a non-reacting jet with a coflow stream is described by means of Large Eddy Simulations (LES) carried out with the computational tool OpenFoam. In order to study the influence of the sub-grid scale (SGS) model on the main flow statistics, Smagorinsky (SMAG) and One Equation Eddy (OEE) approaches are used to model the smallest scales involved in the turbulence of the jet. The impact of cell size and turbulent inlet boundary condition in resulting velocity profiles is analyzed as well. Four different tasks have been performed to accomplish these objectives. Firstly, the simulation of a turbulent pipe, which is necessary to generate and map coherent turbulence structure into the inlet of the non-reacting jet domain. Secondly, a structured mesh based on hexahedrons has been built for the jet and its coflow. The third task consists on performing four different simulations. In those, mapping statistics from the turbulent pipe is compared with the use of fluctuating inlet boundary condition available in OpenFoam; OEE and SMAG approaches are contrasted; and the effect of changing cell size is investigated. Finally, as forth task, the obtained results are compared with experimental data. As main conclusions of this comparison, it has been proved that the fluctuating boundary condition requires much less computational cost, but some inaccuracies were found close to the nozzle. Also, both SGS models are capable to simulate this kind of jets with a co-flow stream with exactitude.