Large Eddy Simulation of the Mixing of a Passive Scalar in a High-Schmidt Turbulent Jet

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Juan M. Mejía ◽  
Amsini Sadiki ◽  
Alejandro Molina ◽  
Farid Chejne ◽  
Pradeep Pantangi
Keyword(s):  
Large Eddy Simulation ◽  
Eddy Diffusivity ◽  
Turbulent Regime ◽  
Scalar Flux ◽  
Water Stream ◽  
Eddy Simulation ◽  
Turbulent Schmidt Number ◽  
Large Eddy ◽  
Number Flow ◽  
Simulation Results

Accurate subgrid-scale (SGS) scalar flux models are essential when large eddy simulation (LES) is used to represent flow, mixing and transport of passive and active scalars in engineering, and environmental applications in turbulent regime. Many SGS scalar flux models have been developed for flows with low Schmidt numbers (Sc), but their application to high Sc flows has important limitations. In high Sc flows, the behavior of the scalar field becomes anisotropic because of intermittency effects, phenomenon that must be accounted for by SGS scalar flux models. The objective of this paper is to evaluate the ability of three SGS scalar flux models to predict the scalar behavior of a high Sc-number flow configuration, namely the anisotropy-resolved SGS scalar flux model: (1) appropriate for high Sc-number flow configurations, and two additional SGS models (linear eddy diffusivity based SGS models) with (2) constant, and (3) dynamically calculated turbulent Schmidt number. The LES simulation results accomplished by these models are compared to each other and to experimental data of a turbulent round jet discharging a diluted scalar into a low-velocity coflowing water stream. The comparison of simulation results and experimental observations shows that, in general, all SGS models reproduce the mean filtered concentration distribution in radial direction. The dynamic eddy diffusivity and anisotropy models reproduce the rms of the concentration and SGS scalar fluxes distribution. In particular, the anisotropy model improves the prediction reliability of LES. However, the three models evaluated in this study cannot accurately predict the scalar behavior at the superviscous layer. Finally, this work demonstrates that complex models can achieve reliable predictions on reasonable grids using less computational effort, while simple models require fine grids with increased computational costs.

scholarly journals Optimization of the Turbulence Model on Numerical Simulations of Flow Field within a Hydrocyclone

2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Yan Xu ◽  
Zunce Wang ◽  
Lin Ke ◽  
Sen Li ◽  
Jinglong Zhang
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Cross Sections ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Computational Grids ◽  
Test Results ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Simulation Results

Reynolds Stress Model and Large Eddy Simulation are used to respectively perform numerical simulation for the flow field of a hydrocyclone. The three-dimensional hexahedral computational grids were generated. Turbulence intensity, vorticity, and the velocity distribution of different cross sections were gained. The velocity simulation results were compared with the LDV test results, and the results indicated that Large Eddy Simulation was more close to LDV experimental data. Large Eddy Simulation was a relatively appropriate method for simulation of flow field within a hydrocyclone.

scholarly journals Direct numerical simulation and large-eddy simulation of stationary buoyancy-driven turbulence

2009 ◽  
Vol 643 ◽  
pp. 279-308 ◽  
Author(s):  
D. CHUNG ◽  
D. I. PULLIN
Keyword(s):  
Numerical Simulation ◽  
Large Eddy Simulation ◽  
Direct Numerical Simulation ◽  
Density Ratio ◽  
Stationary Flow ◽  
Small Scale ◽  
Scalar Flux ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Active Scalar

We report direct numerical simulation (DNS) and large-eddy simulation (LES) of statistically stationary buoyancy-driven turbulent mixing of an active scalar. We use an adaptation of the fringe-region technique, which continually supplies the flow with unmixed fluids at two opposite faces of a triply periodic domain in the presence of gravity, effectively maintaining an unstably stratified, but statistically stationary flow. We also develop a new method to solve the governing equations, based on the Helmholtz–Hodge decomposition, that guarantees discrete mass conservation regardless of iteration errors. Whilst some statistics were found to be sensitive to the computational box size, we show, from inner-scaled planar spectra, that the small scales exhibit similarity independent of Reynolds number, density ratio and aspect ratio. We also perform LES of the present flow using the stretched-vortex subgrid-scale (SGS) model. The utility of an SGS scalar flux closure for passive scalars is demonstrated in the present active-scalar, stably stratified flow setting. The multi-scale character of the stretched-vortex SGS model is shown to enable extension of some second-order statistics to subgrid scales. Comparisons with DNS velocity spectra and velocity-density cospectra show that both the resolved-scale and SGS-extended components of the LES spectra accurately capture important features of the DNS spectra, including small-scale anisotropy and the shape of the viscous roll-off.

Evaluation of the WRF PBL Parameterizations for Marine Boundary Layer Clouds: Cumulus and Stratocumulus

2013 ◽  
Vol 141 (7) ◽  
pp. 2265-2271 ◽  
Author(s):  
Hsin-Yuan Huang ◽  
Alex Hall ◽  
Joao Teixeira
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Marine Boundary Layer ◽  
Layer Structure ◽  
Model Performance ◽  
Simulation Models ◽  
Eddy Diffusivity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Boundary Layer Cloud

Abstract The performance of five boundary layer parameterizations in the Weather Research and Forecasting Model is examined for marine boundary layer cloud regions running in single-column mode. Most parameterizations show a poor agreement of the vertical boundary layer structure when compared with large-eddy simulation models. These comparisons against large-eddy simulation show that a parameterization based on the eddy-diffusivity/mass-flux approach provides a better performance. The results also illustrate the key role of boundary layer parameterizations in model performance.

Large Eddy Simulation of the Flow Field in the Hudson River

2011 ◽  
Author(s):  
Tuy N. M. Phan ◽  
John C. Wells ◽  
William D. Kirkey ◽  
Mohammad S. Islam ◽  
James S. Bonner
Keyword(s):  
New York ◽  
Large Eddy Simulation ◽  
Large Scale ◽  
Acoustic Doppler Current Profiler ◽  
Hudson River ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Current Profiler ◽  
Simulation Results ◽  
Indian Point

Large-eddy simulation (LES) has been conducted under idealized conditions in two river reaches of the Hudson River (New York, USA), with near-bank resolution set to some 5 meters in order to resolve large-scale motions of turbulence in the near-bank regions. To simplify analysis, simulation is performed at a constant discharge corresponding to a typical ebb tide. A standard Smagorinsky model is implemented in the commercial package FLUENT, with buoyancy neglected and bottom roughness set to zero. We perform Proper Orthogonal Decomposition (POD) on the LES results. POD modes are orthogonal flow fields that capture the kinetic energy in an optimally convergent fashion. Results show that only a few POD modes are enough to describe the most energetic flow dynamics. In a reach around the Indian Point power plant, the second and third modes reflect an interesting generation of separating eddies on the western bank, which we do not find with a URANS (standard k-ε) computation on the same grid. To test our simulation, a comparison of simulation results with other simulation results and Acoustic Doppler Current Profiler (ADCP) data measured at West Point, New York will be presented.

Rapid and Slow Decomposition in Large Eddy Simulation of Scalar Turbulence

2010 ◽  
Author(s):  
L. Fang ◽  
L. Shao ◽  
J. P. Bertoglio ◽  
L. P. Lu ◽  
Z. S. Zhang
Keyword(s):  
Large Eddy Simulation ◽  
A Priori ◽  
Scalar Dissipation ◽  
Scalar Flux ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Slow Part ◽  
The Mean ◽  
Subgrid Stress

In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anisotropy affect the subgrid stress via the mean flow gradient. A method of evaluating the mean effects is to split the subgrid stress tensor into “rapid” and “slow” parts. This decomposition was introduced by Shao et al. (1999) and applied to A Priori tests of existing subgrid models in the case of a turbulent mixing layer. In the present work, the decomposition is extended to the case of a passive scalar in inhomogeneous turbulence. The contributions of rapid and slow subgrid scalar flux, both in the equations of scalar variance and scalar flux, are analyzed. A Priori numerical tests are performed in a turbulent Couette flow with a mean scalar gradient. Results are then used to evaluate the performances of different popular subgrid scalar models. It is shown that existing models can not well simulate the slow part and need to be improved. In order to improve the modeling, an extension of the model proposed by Cui et al. (2004) is introduced for the slow part, whereas the Scale-Similarity model is used reproduce the rapid part. Combining both models, A Priori tests lead to a better performance. However, the remaining problem is that none eddy-diffusion model can correctly represent the strong scalar dissipation near the wall. This problem will be addressed in future work.

Real-time flight simulation with highly resolved wind fields from a LES model

2021 ◽  
Author(s):  
Xinying Liu ◽  
Julien Gérard Anet ◽  
Leonardo Manfriani ◽  
Yongling Fu
Keyword(s):  
Large Eddy Simulation ◽  
Energy Management ◽  
Management System ◽  
General Aviation ◽  
Energy Management System ◽  
Energy Reserves ◽  
Wind Fields ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Simulation Results

<p>An overproportioned number of accidents involving general aviation occur in complex terrain. According to the statistics included in the accident investigation reports published by the Swiss Transportation Safety Investigation Board, in some cases, pilots overestimated the energy reserves of their aircraft leading to a loss of control. In order to increase flight safety for private pilots in mountainous regions, on behalf of the Swiss Federal Office of Civil Aviation, the Centre for Aviation (ZAV) at the Zurich University of Applied Sciences  develops an energy management system for general aviation, which displays the remaining airplane’s energy reserves taking into account meteorological information. The research project comprises two phases: i) concept and feasibility study and ii) prototype development. The project is currently running in phase one. In this phase, the first implementation of the energy management system was completed. The system was evaluated in the ZAV’s Research and Didactics Simulator (ReDSim). In order to generate highly resolved wind fields in the ReDsim, a well-established large-eddy simulation model, the Parallelized Large-Eddy Simulation (PALM) framework, was used in the concept study, focusing on a small mountainous region in Switzerland, not far from Samedan. For a more realistic representation of specific meteorological situations, PALM was driven with boundary conditions extracted from the COSMO-1 reanalysis of MeteoSwiss. The environment model in the ReDSim was modified to include a new subsystem simulating atmospheric disturbance. The essential variables (wind components, temperature and pressure) were extractred from the PALM output and fed into the subsystem after interpolation to obtain the values at any instant and any aircraft position. Within the subsystem, it is also possible to generate statistical atmospheric turbulence based on the Dryden turbulence model which refers to the military specification MIL-F-8785. This work focuses on the presentation of the PALM model setup and discusses the COSMO-1 forced PALM simulation results, including a statistical comparison of the simulation results with meteorological data from different meteorological reference stations.</p>

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