Dynamic interaction of multiple buoyant jets

2012 ◽  
Vol 708 ◽  
pp. 539-575 ◽  
Author(s):  
Adrian C. H. Lai ◽  
Joseph H. W. Lee
Keyword(s):  
Stokes Equations ◽  
Dynamic Pressure ◽  
Unit Length ◽  
Iterative Solution ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Dynamic Interaction ◽  
Ambient Conditions ◽  
Buoyant Jet ◽  
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.

An algebraic model for the turbulent flux of a passive scalar

1989 ◽  
Vol 203 ◽  
pp. 77-101 ◽  
Author(s):  
Michael M. Rogers ◽  
Nagi N. Mansour ◽  
William C. Reynolds
Keyword(s):  
Stokes Equations ◽  
Transport Model ◽  
Time Derivative ◽  
Turbulent Channel Flow ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Flux Vector ◽  
Scalar Flux

The behaviour of passive-scalar fields resulting from mean scalar gradients in each of three orthogonal directions in homogeneous turbulent shear flow has been studied using direct numerical simulations of the unsteady incompressible Navier-Stokes equations with 128 × 128 × 128 grid points. It is found that, for all orientations of the mean scalar gradient, the sum of the pressure-scalar gradient and velocity gradient-scalar gradient terms in the turbulent scalar flux balance equation are approximately aligned with the scalar flux vector itself. In addition, the time derivative of the scalar flux is also approximately aligned with the flux vector for the developed fields (corresponding to roughly constant correlation coefficients). These alignments lead directly to a gradient transport model with a tensor turbulent diffusivity. The simulation results are used to fit a dimensionless model coefficient as a function of the turbulence Reynolds and Péclet numbers. The model is tested against two different passive-scalar fields in fully developed turbulent channel flow (also generated by direct numerical simulation) and is found to predict the scalar flux quite well throughout the entire channel.

Direct Numerical Simulation of Mixing of a Passive in Decaying Turbulence

1999 ◽  
Author(s):  
P. Deb ◽  
Pradip Majumdar
Keyword(s):  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Scalar Dissipation ◽  
Step Method ◽  
Fractional Step Method ◽  
Mixing Processes ◽  
Turbulent Reactive Flows ◽  
Decaying Turbulence

Abstract Research on turbulent mixing processes is of great interest to those working on turbulent-reactive flows. In this paper, a detailed study has been performed for the evolution of scalar fields of different initial integral scales in decaying, homogeneous and isotropic turbulence using DNS technique. Passive scalar mixing in a cubical decaying, homogeneous, isotropic turbulence field is considered. The three-dimensional incompressible Navier-Stokes equations together with scalar equation are solved using Fractional Step Method. The convective and diffusive terms in governing equations are discretised by Compact Finite Difference Scheme. The 32 × 32 × 32 uniform staggered grids are used. The present simulation is performed at Taylor Reynolds number of 28.83. In this paper, the evolution of scalar RMS and scalar dissipation rate for different integral length scales has been presented. The initial velocity vector and Probability Density Function (PDF) of scalar at different eddy turn over time have also been presented.

scholarly journals A Code for Simulating Heat Transfer in Turbulent Channel Flow

Mathematics ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 756
Author(s):  
Federico Lluesma-Rodríguez ◽  
Francisco Álcantara-Ávila ◽  
María Jezabel Pérez-Quiles ◽  
Sergio Hoyas
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Turbulent Channel Flow ◽  
Passive Scalar ◽  
Direct Numerical Simulations ◽  
Time Dependent ◽  
Navier Stokes ◽  
Thermal Flow ◽  
Navier Stokes Equations

One numerical method was designed to solve the time-dependent, three-dimensional, incompressible Navier–Stokes equations in turbulent thermal channel flows. Its originality lies in the use of several well-known methods to discretize the problem and its parallel nature. Vorticy-Laplacian of velocity formulation has been used, so pressure has been removed from the system. Heat is modeled as a passive scalar. Any other quantity modeled as passive scalar can be very easily studied, including several of them at the same time. These methods have been successfully used for extensive direct numerical simulations of passive thermal flow for several boundary conditions.

scholarly journals Flow Pressure Behavior Downstream of Ski Jumps

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 168 ◽  
Author(s):  
Agostino Lauria ◽  
Giancarlo Alfonsi ◽  
Ali Tafarojnoruz
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Dynamic Pressure ◽  
Pressure Head ◽  
Navier Stokes ◽  
Maximum Pressure ◽  
Navier Stokes Equations ◽  
Free Jet ◽  
Jet Characteristics ◽  
The Impact

Ski jump spillways are frequently implemented to dissipate energy from high-speed flows. The general feature of this structure is to transform the spillway flow into a free jet up to a location where the impact of the jet creates a plunge pool, representing an area for potential erosion phenomena. In the present investigation, several tests with different ski jump bucket angles are executed numerically by means of the OpenFOAM® digital library, taking advantage of the Reynolds-averaged Navier–Stokes equations (RANS) approach. The results are compared to those obtained experimentally by other authors as related to the jet length and shape, obtaining physical insights into the jet characteristics. Particular attention is given to the maximum pressure head at the tailwater. Simple equations are proposed to predict the maximum dynamic pressure head acting on the tailwater, as dependent upon the Froude number, and the maximum pressure head on the bucket. Results of this study provide useful suggestions for the design of ski jump spillways in dam construction.

Numerical Modeling of Flow Over a Dam Spillway

2006 ◽  
Author(s):  
Iraj Saeedpanah ◽  
M. Shayanfar ◽  
E. Jabbari ◽  
Mohammad Haji Mohammadi
Keyword(s):  
Free Surface ◽  
Stokes Equations ◽  
Iterative Solution ◽  
Free Surface Flows ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Continuity Equations ◽  
Water Jets ◽  
Pressure Fields ◽  
Good Agreement

Free surface flows are frequently encountered in hydraulic engineering problems including water jets, weirs and around gates. An iterative solution to the incompressible two-dimensional vertical steady Navier-Stokes equations, comprising momentum and continuity equations, is used to solve for the priori unknown free surface, the velocity and the pressure fields. The entire water body is covered by a unstructured finite element grid which is locally refined. The dynamic boundary condition is imposed for the free surface where the pressure vanishes. This procedure is done continuously until the normal velocities components vanish. To overcome numerical errors and oscillations encountering in convection terms, the SUPG (streamline upwinding Petrov-Galerkin) method is applied. The solution method is tested for different discharges onto a standard spillway geometries. The results shows good agreement with available experimental data.

Natural Ventilation in a Model Room

2012 ◽  
Vol 4 (1) ◽  
Author(s):  
Sudhakar Subudhi ◽  
K. R. Sreenivas ◽  
Jaywant H. Arakeri
Keyword(s):  
Mathematical Model ◽  
Heat Flux ◽  
Natural Ventilation ◽  
Constant Heat Flux ◽  
Bottom Plate ◽  
Bottom Surface ◽  
Buoyant Jet ◽  
Buoyant Jets ◽  
Fluid Medium ◽  
Model Room

Natural ventilation of a model room with water as the fluid medium is studied. It is insulated by air gaps on the four sides and at the top. A constant heat flux has been maintained on the bottom surface of the room. This room is surrounded by a large exterior tank containing water. There are three openings each on two opposing sides of the model room. For any experiment, only one opening on each side is kept open. Fluid enters or leaves these openings and the flow is driven entirely by buoyancy forces. Shadowgraph technique is used for visualization. The buoyancy causes flow to enter through the bottom opening and leaves through the top opening. At the openings, buoyant jets are observed and which have higher or lower relative density compared with that of its environment. The buoyant jet at the inlet interacts with the plumes on the heated bottom plate. From these visualizations, it appears that free convection at bottom plate will be affected by the buoyant jets at the openings and the degree to which it is affected depends on the position and size of openings and distance between inlet and outlet. The flow rate due to the natural ventilation depends on the bottom surface heat flux and the height difference between the openings. The temperatures of the floor, the interior and the exterior are calculated using a simple mathematical model. The values of temperatures obtained in the experiments are reasonably well predicted by the mathematical model.

Compositional Simulation of Two-Phase Flows for Pipeline Depressurization

SPE Journal ◽  
2017 ◽  
Vol 22 (04) ◽  
pp. 1242-1253 ◽  
Author(s):  
Luigi Raimondi
Keyword(s):  
Numerical Solution ◽  
Mass Balance ◽  
Stokes Equations ◽  
Dynamic Pressure ◽  
Gas Production ◽  
Fluid Composition ◽  
Two Phase ◽  
Compositional Approach ◽  
Liquid Phases ◽  
System Pressure

Summary The simulation of multiphase flow, considered in the case of coexisting vapor and liquid phases, is an important topic in engineering for the design of oil-and-gas production and transportation facilities. This paper presents the development of a compositional approach for the dynamic calculation of multiphase flows in pipelines. This approach can be defined as “full compositional,” because the vapor and liquid phases are described by taking into account the chemical composition, presenting points of interest from both the theoretical and the practical points of view. Physical properties required are calculated at each integration timestep with the actual phase compositions instead of relying on property tables previously generated from a single constant fluid composition. With this approach, in the numerical solution of the conservative two-phase-flow equations, the congruency between the dynamic pressure, calculated by solving the Navier-Stokes equations at constant temperature, and the thermodynamic pressure of the system becomes a critical constraint. In the numerical solution, the overall mass balance defined by means of the vapor- and liquid-phase densities is verified with respect to the mass balance of each chemical component involved, and the system pressure obtained from the solution of the momentum equations is always compared with the thermodynamic value defined by mass balance. Of the numerous test cases created for model validation, three of them (focused on fast depressurizations) are presented and discussed. Similar examples are not available in the literature as solutions of the current “state-of-the-art” commercial pipeline simulators.

Three-Dimensional Buoyant Wall Jets Released Into a Coflowing Turbulent Boundary Layer

1990 ◽  
Vol 112 (2) ◽  
pp. 356-362 ◽  
Author(s):  
J. R. Sinclair ◽  
P. R. Slawson ◽  
G. A. Davidson
Keyword(s):  
Three Dimensional ◽  
Ground Level ◽  
Turbulent Shear ◽  
Wall Jet ◽  
Turbulent Shear Flow ◽  
Streamwise Vorticity ◽  
Buoyant Jet ◽  
Buoyant Jets ◽  
Jet Trajectory ◽  
Model Predictions

Experiments have been conducted in a water flume to simulate finite-length line sources of heat that issue horizontally at ground level into a coflowing turbulent shear flow. The downstream development of each buoyant jet is documented by detailed mean temperature measurements, which are analyzed to determine the jet trajectory, spread rates, and distance to the point of liftoff from the surface. In addition, a three-dimensional, parabolic, numerical model based on the fundamental conservation equations is developed. Model predictions of several buoyant jets compare reasonably with the experimental data and suggest that the strength of the streamwise vorticity plays an important role in governing liftoff of a buoyant wall jet from the surface.

Application of spectral proper orthogonal decomposition to velocity and passive scalar fields in a swirling coaxial jet

2020 ◽  
Vol 32 (1) ◽  
pp. 015106 ◽  
Author(s):  
Pravin Ananta Kadu ◽  
Yasuhiko Sakai ◽  
Yasumasa Ito ◽  
Koji Iwano ◽  
Masatoshi Sugino ◽  
...  
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Orthogonal Decomposition ◽  
Proper Orthogonal
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