Numerical study of stable stratification effects on the wind over simplified tall building models using large-eddy simulations

2021 ◽  
Vol 193 ◽  
pp. 107625
Author(s):  
Zhenqing Liu ◽  
Weipeng Li ◽  
Lian Shen ◽  
Yan Han ◽  
Zhiwen Zhu ◽  
...  
Keyword(s):  
Numerical Study ◽  
Stable Stratification ◽  
Tall Building ◽  
Large Eddy Simulations ◽  
Building Models ◽  
Large Eddy

Analysis and modelling of subgrid-scale motions in near-wall turbulence

1998 ◽  
Vol 356 ◽  
pp. 327-352 ◽  
Author(s):  
CARLOS HÄRTEL ◽  
LEONHARD KLEISER
Keyword(s):  
Eddy Viscosity ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Large Eddy Simulations ◽  
Inverse Cascade ◽  
Large Eddy ◽  
Wall Flow ◽  
Definition Of ◽  
Subgrid Stress ◽  
Near Wall

A numerical study of turbulent channel flow at various Reynolds numbers (Reτ=115, 210, 300) is conducted in order to examine the requirements for a reliable subgrid modelling in large-eddy simulations of wall-bounded flows. Using direct numerical simulation data, the interactions between large and small scales in the near-wall flow are analysed in detail which sheds light on the origin of the inverse cascade of turbulent kinetic energy observed in the buffer layer. It is shown that the correlation of the wall-normal subgrid stress and the wall-normal derivative of the streamwise grid-scale velocity plays the key role in the occurrence of the inverse cascade. A brief a priori test of several subgrid models shows that currently applied models are not capable of accounting properly for the complex interactions in the near-wall flow. A series of large-eddy simulations gives evidence that this deficiency may cause significant errors in important global quantities of the flow such as the mean wall shear stress. A study of the eddy-viscosity ansatz is conducted which reveals that the characteristic scales usually employed for the definition of the eddy viscosity are inappropriate in the vicinity of a wall. Therefore, a novel definition of the eddy viscosity is derived from the analysis of the near-wall energy budget. This new definition, which employs the wall-normal subgrid stress as a characteristic scale, is more consistent with the near-wall physics. No significant Reynolds-number effects are encountered in the present analysis which suggests that the findings may be generalized to flows at higher Reynolds numbers.

Is the water vapor supersaturation distribution Gaussian?

2021 ◽  
Author(s):  
Subin Thomas ◽  
Prasanth Prabhakaran ◽  
Will Cantrell ◽  
Raymond A. Shaw
Keyword(s):  
Water Vapor ◽  
Large Eddy Simulation ◽  
Gaussian Distribution ◽  
Numerical Study ◽  
Mixing Model ◽  
Large Eddy Simulations ◽  
Mixing Processes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Vapor Supersaturation

AbstractWater vapor supersaturation in the atmosphere is produced in a variety of ways, including the lifting of a parcel or via isobaric mixing of parcels. However, irrespective of the mechanism of production, the water vapor supersaturation in the atmosphere has typically been modeled as a Gaussian distribution. In the current theoretical and numerical study, the nature of supersaturation produced by mixing processes is explored. The results from large eddy simulation and a Gaussian mixing model reveal the distribution of supersaturations produced by mixing to be negatively skewed. Further, the causes of skewness are explored using large eddy simulations (LES) and the Gaussian mixing model (GMM). The correlation in forcing of temperature and water vapor fields is recognized as playing a key role.

scholarly journals Intercomparison of Large-Eddy Simulations of the Antarctic Boundary Layer for Very Stable Stratification

2020 ◽  
Vol 176 (3) ◽  
pp. 369-400
Author(s):  
Fleur Couvreux ◽  
Eric Bazile ◽  
Quentin Rodier ◽  
Björn Maronga ◽  
Georgios Matheou ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Stable Stratification ◽  
Large Eddy Simulations ◽  
Large Eddy ◽  
Antarctic Boundary Layer ◽  
The Antarctic

Numerical Study of the Turbulent Flow Inside an ORACLES Configuration

2012 ◽  
Vol 79 (5) ◽  
Author(s):  
Fethi Bouras ◽  
Azeddine Soudani ◽  
Mohamed Si-Ameur
Keyword(s):  
Eddy Viscosity ◽  
Numerical Study ◽  
Longitudinal Velocity ◽  
Large Eddy Simulations ◽  
The European Union ◽  
Combustion Chambers ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Recirculation Zones ◽  
Air Channels

This numerical investigation deals with the validation of the experimental results in the inert cases of Nguyen et al., obtained in the framework of the European Union-funded research program MOLECULES (Modelling of Low Emissions Combustors Using Large Eddy Simulations). This study is based on the benchmark of testing one rig for accurate comparisons with large eddy simulations configuration (ORACLES), aimed at helping the design of reliable lean premixed prevaporized) combustion chambers and supplied with two identical flows of air channels. Therefore, this study is based on the 3D numerical simulation using large eddy simulation-wall adapting local eddy viscosity (LES-WALE) model that aims to determine the longitudinal velocity, the longitudinal velocity fluctuation and the length of recirculation zone for the three cases of flow in different inlet Reynolds (Re = 25,000, 50,000, 75,000). Calculations are carried out by the FLUENT_CFD. The results obtained are compared with experimental measurements of Nguyen et al. The LES_WALE eddy viscosity computation presents a good agreement with the experimental data where we could observe the asymmetrical flow and also detect the recirculation zones and the differences between the cases of the flow.

The Effect of Stratification Ratio on the Macrostructure of Stratified Swirl Flames: Experimental and Numerical Study

2018 ◽  
Author(s):  
Xiao Han ◽  
Davide Laera ◽  
Aimee S. Morgans ◽  
Yuzhen Lin ◽  
Chih-Jen Sung
Keyword(s):  
Fluid Dynamics ◽  
Numerical Study ◽  
Large Eddy Simulations ◽  
Flame Dynamics ◽  
Large Eddy ◽  
Swirling Flame ◽  
Different Shapes ◽  
Flame Quenching ◽  
Simulation Results ◽  
Good Agreement

The present article reports experimental and numerical analyses of the macrostructures featured by a stratified swirling flame for varying stratification ratio (SR). The studies are performed with the Beihang Axial Swirler Independently-Stratified (BASIS) burner, a novel double-swirled full-scale burner developed at Beihang University. Experimentally, it is found that depending on the ratio between the equivalence ratios of the methane-air mixtures from the two swirlers, the flame stabilizes with three different shapes: attached V–flame, attached stratified flame and lifted flame. In order to better understand the mechanisms leading to the three macrostructures, large eddy simulations (LES) simulations are performed via the open source Computational Fluid Dynamics software OpenFOAM using the incompressible solver Reacting Foam. Changing the SR, simulation results show good agreement with experimentally observed time-averaged flame shapes, demonstrating that the incompressible LES are able to fully characterize the different flame behaviours observed in stratified burners. When the LES account for heat loss from walls, they better capture the experimentally observed flame quenching in the outer shear layer. Finally, insights into the flame dynamics are provided by analysing probes located near the two separate streams.

Numerical Study of the Mixing Inside a Jet Stirred Reactor using Large Eddy Simulations

2018 ◽  
Vol 102 (2) ◽  
pp. 331-343
Author(s):  
Ghazaleh Esmaeelzade ◽  
Kai Moshammer ◽  
Ravi Fernandes ◽  
Detlev Markus ◽  
Holger Grosshans
Keyword(s):  
Numerical Study ◽  
Large Eddy Simulations ◽  
Stirred Reactor ◽  
Large Eddy

Numerical study of compact debris in tornadoes at different stages using large eddy simulations

2021 ◽  
Vol 210 ◽  
pp. 104530
Author(s):  
Zhenqing Liu ◽  
Yiwen Cao ◽  
Bowen Yan ◽  
Xugang Hua ◽  
Zhiwen Zhu ◽  
...  
Keyword(s):  
Numerical Study ◽  
Large Eddy Simulations ◽  
Large Eddy
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