The negatively buoyant wall-jet: LES results

Addad, Yacine; Benhamadouche, Sofiane; Laurence, Dominique

doi:10.1016/j.ijheatfluidflow.2004.05.008

Cited by 33 publications

(24 citation statements)

References 11 publications

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“…LES grid resolution has been assessed using prior RANS simulations by Addad et al [13] for a buoyancy-opposed wall-jet and by Van Maele and Merci [14] for a tunnel fire. In both cases, they examined the ratio of the integral turbulence length scale l I = k 3 / 2 ε (determined from the RANS simulation) to the filter width , and found that l I needed to be greater than around 12 for the LES to be well resolved.…”

Section: Grid Resolution Measuresmentioning

confidence: 99%

“…2 a Ratio of the integral length scale to the computational grid cell size calculated using steady RANS on fine grid; b ratio of resolved to total turbulent kinetic energy for the DES The ratios are smaller for the medium and coarse grids, which have values in the plume region of around 6 and 4 respectively. Since it is recommended [13,14] that l I exceed 12 for well-resolved LES, this implies that even the fine grid is relatively coarse in the these simulations.…”

Section: Example Application Of Grid Resolution Measuresmentioning

confidence: 99%

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Reliability Issues of LES-Related Approaches in an Industrial Context

Gant

2009

Flow Turbulence Combust

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Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES) andScale-Adaptive Simulation (SAS) are increasingly being used as engineering tools to predict the behaviour of complex industrial flows. Often the flows studied have not been examined previously and the required grid resolution is unknown. Industrial users studying these flows tend to be using commercial CFD codes and do not usually have access to high-performance computing facilities. Due to the significant computing times required, it is difficult to undertake systematic grid-dependence studies. There is therefore a risk that LES, DES and SAS will be performed using overly coarse grids which may lead to unreliable predictions. The present work surveys a number of practical techniques that provide a means of assessing the quality of the grid resolution in large-eddy simulations and related approaches. To examine the usefulness of these techniques, a gas release in a ventilated room is examined using DES and SAS. The grid resolution measures indicate that overall the grids used are relatively coarse. Both DES and SAS model predictions are found to be in poor agreement with experimental data compared to steady and unsteady Reynoldsaveraged Navier-Stokes (RANS) results using the SST model. The SAS model also shows the greatest grid sensitivity of the four models tested. The work highlights the need for grid-dependence studies and the potential problems of using coarse grids.

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Section: Grid Resolution Measuresmentioning

confidence: 99%

Section: Example Application Of Grid Resolution Measuresmentioning

confidence: 99%

Reliability Issues of LES-Related Approaches in an Industrial Context

Gant

2009

Flow Turbulence Combust

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“…Recently, for example, even a separated turbulent flow over a forward-backward facing step has been successfully simulated with LES by Addad et al 9) They also demonstrated in a different study that the same LES could be applied to accurately simulate a buoyant wall-jet. 10) Since the present flow geometry is a combination of separated flow and curved wall-jet, it is expected that LES is capable of producing reliable computational results for the flow geometry of our concern.…”

Section: Numerical Analysis Of 3-d Unsteady Compressiblementioning

confidence: 99%

A Noble Gas Wiping System to Prevent the Edge Overcoating in Continuous Hot-dip Galvanizing

Ahn

Chung

2006

ISIJ Int.

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A noble method is proposed to prevent the edge overcoating (EOC) that may develop near the edge of the steel strip in the gas wiping process of continuous hot-dip galvanizing. In our past study (ISIJ International, Vol. 27 (2003), No. 10, pp. 1495No. 10, pp. -1501, it was found that the EOC is caused by the alternating vortices which are generated by the collision of two opposing jets in the region outside the steel strip. In the present study, the flow field around the gas wiping system has been analyzed numerically and it was found that when the two opposing jets collide at an angle much less than 180°, the alternating vortices disappear and the impinging pressure on the steel strip surface becomes nearly uniform. In order to deflect both jets downward by a certain angle, a cylinder with small diameter is installed tangentially to each exit of the lower lips of the two-dimensional opposing jets. The three dimensional flow field with the proposed device is analyzed numerically by using the commercial CFD software, STAR-CD. And the coating thickness is calculated by solving the boundary layer momentum equation with an integral analysis method. In order to compare the present noble method with the conventional edge baffle plate method to prevent the EOC, the flow field with edge baffle plates is also calculated. The calculation results show that the tangentially installed cylinder at the lower lip of the jet exit is significantly more effective than the edge baffle plate.KEY WORDS: continuous hot-dip galvanizing; edge overcoating; impinging jet; gas wiping.In the present study, the 3-D unsteady compressible turbulent flow field with the proposed configuration with a pair of cylinders in the continuous hot-dip galvanizing system is simulated by using a commercial CFD software, to find out how the cylinder affects the flow behavior of the wiping gas. The simulation results for the impinging pressure and the shear stress on the steel strip surface are used to calculate the thickness of the adhered zinc film by the noble integral analysis method of the boundary layer momentum equation. 7) In addition, the flow field generated by the edge baffle plate is also analyzed to compare its performance for reduction of the EOC with that of the cylinder installed at the lower lip of the air knife nozzle. Numerical Analysis Numerical Analysis of 3-D Unsteady CompressibleFlow In the continuous hot-dip galvanizing process, a heattreated steel strip is passed through a molten zinc bath and the molten zinc is adhered on the steel strip surfaces. Usually, the thickness of the adhered zinc film is nearly 10 times thicker than desired one, and the excessive zinc is removed by nitrogen gas jets. This wiping gas jet system is often called the air knife system. Usually, the Mach number of the nitrogen gas flow is in a range of 0.3-0.6. Therefore, in addition to the continuity and momentum equations, the equation of state and the energy equation are needed. Large Eddy Simulation (LES) is used to solve the turbulent equations, of which f...

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“…The complexity of jet configurations varies from laminar plane jets to buoyant turbulent jets (Rodi, 1982), impinging jets (Chung et al, 2002), and wall jets (Addad et al, 2005), etc. Depending upon the inlet conditions, the jet typically consists of the near-field laminar flow, the far-field turbulent flow, and the transition from the laminar to turbulent flow in between the near and far fields.…”

Section: Introductionmentioning

confidence: 99%