scholarly journals Idealized Numerical Simulations of the Interactions between Buoyant Plumes and Density Currents

2007 ◽  
Vol 64 (6) ◽  
pp. 2105-2115 ◽  
Author(s):  
Philip Cunningham
Keyword(s):  
Vertical Velocity ◽  
Dynamical Behavior ◽  
Sea Breeze ◽  
Density Current ◽  
Buoyant Plume ◽  
Density Currents ◽  
Buoyant Plumes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Idealized numerical experiments using a large-eddy simulation (LES) model are performed to examine the fundamental dynamical processes associated with the interactions between buoyant plumes and density currents. The aim of these simulations is to provide insight into the rapid changes in the structure of plumes that may be observed during the passage of density current phenomena such as thunderstorm outflows, sea-breeze fronts, or intense cold fronts. The LES model results indicate that when the ambient winds are calm the vertical velocity in the plume decreases with the passage of the density current, but that when the ambient winds oppose the motion of the density current a significant increase in vertical velocity in the plume may occur temporarily. In the latter case, the pressure perturbation and the associated region of horizontal convergence that lead the head of the density current interact with the tilted plume, causing the base of the plume to become vertical and resulting in a dramatic increase in vertical velocity within the plume. This basic dynamical behavior occurs over a relatively broad range of parameters, provided the characteristic velocity in the density current (taken as the densimetric speed) exceeds the ambient wind speed. When this is the case, the interaction is dominated by the effect of the density current on the buoyant plume such that the plume is essentially advected as a passive tracer by the flow due to the density current, and the increase in vertical velocity depends on the inverse of the convective Froude number of the buoyant plume.

Large-Eddy Simulation of the Onset of the Sea Breeze

2007 ◽  
Vol 64 (12) ◽  
pp. 4445-4457 ◽  
Author(s):  
M. Antonelli ◽  
R. Rotunno
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Large Scale ◽  
Three Dimensional ◽  
Sea Breeze ◽  
Small Scale ◽  
Computational Domain ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Abstract This paper describes results from a large-eddy simulation (LES) model used in an idealized setting to simulate the onset of the sea breeze. As the LES is capable of simulating boundary layer–scale, three-dimensional turbulence along with the mesoscale sea-breeze circulation, a parameterization of the planetary boundary layer was unnecessary. The basic experimental design considers a rotating, uniformly stratified, resting atmosphere that is suddenly heated at the surface over the “land” half of the domain. To focus on the simplest nontrivial problem, the diurnal cycle, effects of moisture, interactions with large-scale winds, and coastline curvature were all neglected in this study. The assumption of a straight coastline allows the use of a rectangular computational domain that extends to 50 km on either side of the coast, but only 5 km along the coast, with 100-m grid intervals so that the small-scale turbulent convective eddies together with the mesoscale sea breeze may be accurately computed. Through dimensional analysis of the simulation results, the length and velocity scales characterizing the simulated sea breeze as functions of the externally specified parameters are identified.

Larger-Eddy Simulation of Velocity Fluctuation in a Mixing T-Junction

2012 ◽  
Vol 152-154 ◽  
pp. 1313-1318
Author(s):  
Tao Lu ◽  
Su Mei Liu ◽  
Ping Wang ◽  
Wei Yyu Zhu
Keyword(s):  
Experimental Data ◽  
Velocity Fluctuation ◽  
Flow Model ◽  
Numerical Results ◽  
Mean Square ◽  
Main Duct ◽  
Velocity Fluctuations ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Velocity fluctuations in a mixing T-junction were simulated in FLUENT using large-eddy simulation (LES) turbulent flow model with sub-grid scale (SGS) Smagorinsky–Lilly (SL) model. The normalized mean and root mean square velocities are used to describe the time-averaged velocities and the velocities fluctuation intensities. Comparison of the numerical results with experimental data shows that the LES model is valid for predicting the flow of mixing in a T-junction junction. The numerical results reveal the velocity distributions and fluctuations are basically symmetrical and the fluctuation at the upstream of the downstream of the main duct is stronger than that at the downstream of the downstream of the main duct.

scholarly journals Demistify: a large-eddy simulation (LES) and single-column model (SCM) intercomparison of radiation fog

2022 ◽  
Vol 22 (1) ◽  
pp. 319-333
Author(s):  
Ian Boutle ◽  
Wayne Angevine ◽  
Jian-Wen Bao ◽  
Thierry Bergot ◽  
Ritthik Bhattacharya ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Weather Prediction ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Radiation Fog ◽  
Eddy Simulation ◽  
Cloud Droplet Size Distribution ◽  
Large Eddy ◽  
Single Column ◽  
Les Model

Abstract. An intercomparison between 10 single-column (SCM) and 5 large-eddy simulation (LES) models is presented for a radiation fog case study inspired by the Local and Non-local Fog Experiment (LANFEX) field campaign. Seven of the SCMs represent single-column equivalents of operational numerical weather prediction (NWP) models, whilst three are research-grade SCMs designed for fog simulation, and the LESs are designed to reproduce in the best manner currently possible the underlying physical processes governing fog formation. The LES model results are of variable quality and do not provide a consistent baseline against which to compare the NWP models, particularly under high aerosol or cloud droplet number concentration (CDNC) conditions. The main SCM bias appears to be toward the overdevelopment of fog, i.e. fog which is too thick, although the inter-model variability is large. In reality there is a subtle balance between water lost to the surface and water condensed into fog, and the ability of a model to accurately simulate this process strongly determines the quality of its forecast. Some NWP SCMs do not represent fundamental components of this process (e.g. cloud droplet sedimentation) and therefore are naturally hampered in their ability to deliver accurate simulations. Finally, we show that modelled fog development is as sensitive to the shape of the cloud droplet size distribution, a rarely studied or modified part of the microphysical parameterisation, as it is to the underlying aerosol or CDNC.

scholarly journals The Lagrangian ice microphysics code LCM: Introduction, current developments and benefits

2020 ◽  
Author(s):  
Simon Unterstrasser
Keyword(s):  
Crystal Growth ◽  
Turbulent Dispersion ◽  
Eddy Simulation ◽  
Ice Nuclei ◽  
Large Eddy ◽  
Radiative Impact ◽  
Ice Microphysics ◽  
Microphysical Processes ◽  
Aerosol Module ◽  
Les Model

<p>The Lagrangian Cirrus Module (LCM) is a Lagrangian (also known as particle-based) ice microphysics code that is fully coupled to the large-eddy simulation (LES) code EULAG. The ice phase is described by a large number of simulation particles (order 10<sup>6</sup> to10<sup>9</sup>) which act as surrogates for the real ice crystals. The simulation particles (SIPs) are advected and microphysical processes like deposition/sublimation and sedimentation are solved for each individual SIP. More specifically, LCM treats ice nucleation, crystal growth, sedimentation, aggregation, latent heat release, radiative impact on crystal growth, and turbulent dispersion. The aerosol module comprises an explicit representation of size-resolved non-equilibrium aerosol microphysical processes for supercooled solution droplets and insoluble ice nuclei.</p><p>First, an general introduction to particle-based microphysics coupled to a grid-based (Eulerian) LES model is given.<br>In the following, emphasis is put on highlighting the benefits of the Lagrangian approach by presenting a variety of simulation examples.</p>

scholarly journals Supersaturation calculation in large eddy simulation models for prediction of the droplet number concentration

2012 ◽  
Vol 5 (3) ◽  
pp. 761-772 ◽  
Author(s):  
O. Thouron ◽  
J.-L. Brenguier ◽  
F. Burnet
Keyword(s):  
Cloud Condensation Nuclei ◽  
Simulation Models ◽  
Number Concentration ◽  
Eddy Simulation ◽  
Droplet Concentration ◽  
Large Eddy ◽  
Condensed Water ◽  
Les Model ◽  
Adjustment Scheme ◽  
Cloud Core

Abstract. A new parameterization scheme is described for calculation of supersaturation in LES models that specifically aims at the simulation of cloud condensation nuclei (CCN) activation and prediction of the droplet number concentration. The scheme is tested against current parameterizations in the framework of the Meso-NH LES model. It is shown that the saturation adjustment scheme, based on parameterizations of CCN activation in a convective updraft, overestimates the droplet concentration in the cloud core, while it cannot simulate cloud top supersaturation production due to mixing between cloudy and clear air. A supersaturation diagnostic scheme mitigates these artefacts by accounting for the presence of already condensed water in the cloud core, but it is too sensitive to supersaturation fluctuations at cloud top and produces spurious CCN activation during cloud top mixing. The proposed pseudo-prognostic scheme shows performance similar to the diagnostic one in the cloud core but significantly mitigates CCN activation at cloud top.

Flow Patterns and Temperature Distribution in an Underground Metro Station

2018 ◽  
Author(s):  
Alaa Hasan ◽  
Tarek ElGammal ◽  
Ryoichi S. Amano ◽  
Essam E. Khalil
Keyword(s):  
Thermal Comfort ◽  
Thermal Conditions ◽  
Large Space ◽  
Metro Station ◽  
Air Conditioning System ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Set Up ◽  
Les Model

Accurate control of thermal conditions in large space buildings like an underground metro station is a significant issue because passengers’ thermal comfort must be maintained at a satisfactory level. The large eddy simulation (LES) model was adopted while using the computational fluid dynamics (CFD) software “STAR CCM+” to set up a CFD station model to predict static air temperature, velocity, relative humidity and predicted mean vote (PMV), which indicates the passengers’ thermal comfort. The increase in the number of passengers using the model station is taken into consideration. The studied cases covered all the possible modes of the station box, these modes are (1) the station box is empty of trains, (2) the presence of one train inside the station box, (3) the presence of two trains inside the station box. The objective is to bring the passengers’ thermal comfort in all modes to the acceptable level. The operation of under platform exhaust (UPE) system is considered in case of train presence inside the station box. The use of UPE is more energy efficient than depending entirely on the air conditioning system to maintain the thermal conditions comfortable.

Accuracy Verification of the Turbulent Flame LES Model by a Methane/Air Burner Flame

2015 ◽  
Author(s):  
Murase Kagenobu ◽  
Oshima Nobuyuki ◽  
Takahashi Yusuke
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Counter Flow ◽  
Flamelet Model ◽  
Eddy Simulation ◽  
Partially Premixed Combustion ◽  
Large Eddy ◽  
Burner Flame ◽  
Les Model

This paper focuses on the numerical simulation of Sandia National Laboratories “the piloted methane/air burner flame D.” Large Eddy Simulation and 2-scalar flamelet approach are applied for the turbulent and partially premixed combustion field, which is expressed by the LES filtered equations of scalar G for tracking the flame surfaces and mixture fraction of a fuel and an oxidizer. The flamelet data consists of temperature, specific volume and laminar flame speed are calculated by the detail chemical reaction with GRI-Mech 3.0. Two kinds of flamelet data are validated; one is “equilibrium flamelet data” calculated by 0-dimensional equilibrium solution based on equilibrium model; the other is “diffusion flamelet data” calculated by 1-dimensional counter flow solution based on laminar flamelet model. Consequently, the “diffusion flamelet data” gives better result in this type of combustion field.

The Germano Large Eddy Simulation Model Used for the Simulation of Separated Flow

2003 ◽  
Author(s):  
Engin Cetindogan ◽  
Govert de With ◽  
Arne E. Holdo̸
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Computational Study ◽  
Separated Flow ◽  
Local Flow ◽  
Large Eddy Simulation Model ◽  
Slip Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

A computational study of unsteady, separated fluid flow was made using the Large Eddy Simulation (LES). As flow problem the turbulent flow past a circular cylinder at a Reynolds number of Re = 3900 was chosen. The objective of this work was to study the numerical and modelling aspects of the dynamic Germano-LES turbulence model. Before LES can be used for applications of practical relevance, such as the flow around a complete aircraft or automobile, extensive tests must be carried out on simpler configurations to understand the quality of LES. Also, the influence of different grid resolutions was examined. Due to the fact of a low Reynolds number, no-slip boundary conditions were used at solid walls. Two different subgrid scale models were applied. In recent years several simulations were carried out using the Smagorinsky-LES model but there is still a lack of experience using the dynamic Germano-LES model, which takes the local flow parameters into account. Several simulations with different parameters and grid-models were carried out both with the Germano-LES model and the Smagorinsky-LES model. Comparisons were made between these two models as well as with several experimental data taken from literature.

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