EVALUATION OF PARTICLE STOCHASTIC SEPARATED FLOW MODELS VIA LARGE EDDY SIMULATION

2010 ◽  
Vol 21 (07) ◽  
pp. 867-890 ◽  
Author(s):  
BING WANG ◽  
HUIQIANG ZHANG ◽  
XILIN WANG
Keyword(s):  
Time Series ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Spatial Dispersion ◽  
Computational Cost ◽  
Separated Flow ◽  
Particle Dispersion ◽  
Two Phase ◽  
Eddy Simulation ◽  
Large Eddy

This paper evaluates three widely used particle stochastic separated flow (SSF) models through large eddy simulation (LES) of gas-particle two-phase turbulent flows over a backward-facing step. The ability of the models to predict mean velocities, fluctuating velocities, and spatial dispersion of particles are carefully examined in comparison with LES reference results. Evaluation shows that the improved time-series SSF model produces good predictions on mean and fluctuating velocities in the particle phase which highly agree with LES results. However, the time-series SSF model has higher computational cost. Further, compared with the two other models, the time-series SSF model predicts better results on the spatial dispersion of particles. It has an overall advantage in terms of accuracy and efficiency in predicting velocity moments and particle dispersion even without the presence of so many particles. The dependence of different SSF models on the number of computational particles in a converged flow field is also discussed. This paper is useful for the selection and application of SSF models in numerical simulations of practical two-phase turbulent flows.

Large Eddy Simulation of Gas-Liquid Two-Phase Flow for a Nested Type Fixed-Cone Valve

2012 ◽  
Vol 170-173 ◽  
pp. 2458-2463
Author(s):  
Y.L. Liu ◽  
B. Lv ◽  
W.L. Wei
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Free Fluid ◽  
Step Method ◽  
Fractional Step Method ◽  
Two Phase ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Volume Method ◽  
Free Fluid Surface

large eddy simulation cooperated with a physical fractional-step method is applied to simulate steady flow around a nested type fixed-cone valve; and the equations are solved with the finite volume method. The free fluid surface is simulated by the VOF method. The pressure contours and vorticity magnitude are obtained. The modeling results conform to physical law, and show that the large eddy simulation theory has powerful capacity in simulation of microstructures of turbulent flows, and the function of the nested type fixed-cone valve for energy dissipating is good.

Investigation of Particle-Laden Flow in a Straight Duct Using Large Eddy Simulation

2007 ◽  
Author(s):  
M. Fairweather ◽  
J. Yao
Keyword(s):  
Large Eddy Simulation ◽  
Fluid Phase ◽  
Particle Dispersion ◽  
Secondary Flows ◽  
Solid Particles ◽  
Duct Flow ◽  
Mean Flow ◽  
Two Phase ◽  
Eddy Simulation ◽  
Large Eddy

A particle-laden turbulent flow in a square duct is predicted using large eddy simulation (LES). The simulation is performed for a Reynolds number of 35,500, and correctly predicts the existence of secondary flows and their effects on the mean flow. The results are also in good qualitative agreement with experimental data obtained at different Reynolds numbers. One-way coupling is assumed between solid particles and the fluid, and a particle equation of motion, including Stokes drag, lift, buoyancy and gravity force terms, solved using a Lagrangian particle tracking technique. Three sizes of particle (1, 50 and 100 μm) are considered, and results demonstrate that size has a significant effect on particle dispersion and deposition in the duct flow. As particle size increases, therefore, they tend to settle on the floor of the duct, with less dispersion in the fluid phase. The study demonstrates the usefulness of LES for nuclear waste processing applications since secondary flows occur in many practically-relevant flows, and since it is desirable that the two-phase waste mixture is kept as homogeneous as possible to prevent, or at least discourage, the settling out of solid particles to form a bed which can promote pipe blockages.

An Improvement of a Cavitation Model and the Application to LES

2008 ◽  
Author(s):  
Shin-Ichi Tsuda ◽  
Naoki Tani ◽  
Nobuhiro Yamanishi ◽  
Chisachi Kato
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Volume Fraction ◽  
Computational Cost ◽  
High Accuracy ◽  
Cavitation Model ◽  
Trade Off ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Future Potential

In this paper, we have improved a cavitation model implemented in “Front Flow/Blue (FFB)”, which is a solver of turbulent flows using the large-eddy simulation (LES) technique with high accuracy. To improve the cavitation model, we have carried out a survey of conventional cavitation models and performed a trade-off between the models based on some evaluation points such as accuracy, achievement, future potential, and computational cost. In the new cavitation model, the surface area of cavitation bubbles in each cell is also solved in addition to the volume fraction of the bubbles. Although the validation is in progress, the new cavitation model is expected to be useful to reproduce a detailed cavitation structure.

Large-eddy simulation of turbulence and particle dispersion inside the canopy roughness sublayer

2014 ◽  
Vol 753 ◽  
pp. 499-534 ◽  
Author(s):  
Ying Pan ◽  
Marcelo Chamecki ◽  
Scott A. Isard
Keyword(s):  
Large Eddy Simulation ◽  
Drag Coefficient ◽  
Turbulent Flows ◽  
Fungal Spores ◽  
Particle Dispersion ◽  
Roughness Sublayer ◽  
Quadrant Analysis ◽  
Eddy Simulation ◽  
Velocity Statistics ◽  
Large Eddy

AbstractModelling the dispersion of small particles such as fungal spores, pollens and small seeds inside and above plant canopies is important for many applications. Transport of these particles is driven by strongly inhomogeneous and non-Gaussian turbulent flows inside the canopy roughness sublayer, the region that extends from the ground to approximately three canopy heights. A large-eddy simulation (LES) approach is refined to study particle dispersion within and above the canopy region. Effects of plant reconfiguration are parameterized through a velocity-dependent drag coefficient, which is shown to be critical for accurate reproduction of velocity statistics and mean spore concentrations. The model yields predictions of turbulence statistics that are in good agreement with measurements. This is particularly true of the stress fractions carried by strong events, as revealed by standard quadrant analysis of the resolved velocity fluctuations, which is a known weakness of earlier LES studies of canopy flow using a constant drag coefficient. Experimental data on spore dispersal inside and above a maize canopy are reproduced successfully as well. Characteristics of the particle plume are analysed using LES results, and a pre-existing theoretical framework is adapted to model particle dispersal above the canopy. The results suggest that the plume above the canopy can be approximated using a simple analytical solution if the fraction of spores that escape the canopy region is known. Source height and gravitational settling have strong effects on the plume inside the canopy region and consequently determine the escape fraction. These effects are parameterized in the theoretical model by using the escape fraction to rescale the source strength.

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