scholarly journals Large-eddy Simulation Of A Large-scale Methane Pool Fire

2005 ◽  
Vol 8 ◽  
pp. 963-974 ◽  
Author(s):  
S. Ferraris ◽  
J. Wen ◽  
S. Dembele
2021 ◽  
Vol 33 (8) ◽  
pp. 085109
Author(s):  
Stefan P. Domino ◽  
John Hewson ◽  
Robert Knaus ◽  
Mike Hansen

2017 ◽  
Vol 17 (11) ◽  
pp. 7261-7276 ◽  
Author(s):  
Tobias Wolf-Grosse ◽  
Igor Esau ◽  
Joachim Reuder

Abstract. Street-level urban air pollution is a challenging concern for modern urban societies. Pollution dispersion models assume that the concentrations decrease monotonically with raising wind speed. This convenient assumption breaks down when applied to flows with local recirculations such as those found in topographically complex coastal areas. This study looks at a practically important and sufficiently common case of air pollution in a coastal valley city. Here, the observed concentrations are determined by the interaction between large-scale topographically forced and local-scale breeze-like recirculations. Analysis of a long observational dataset in Bergen, Norway, revealed that the most extreme cases of recurring wintertime air pollution episodes were accompanied by increased large-scale wind speeds above the valley. Contrary to the theoretical assumption and intuitive expectations, the maximum NO2 concentrations were not found for the lowest 10 m ERA-Interim wind speeds but in situations with wind speeds of 3 m s−1. To explain this phenomenon, we investigated empirical relationships between the large-scale forcing and the local wind and air quality parameters. We conducted 16 large-eddy simulation (LES) experiments with the Parallelised Large-Eddy Simulation Model (PALM) for atmospheric and oceanic flows. The LES accounted for the realistic relief and coastal configuration as well as for the large-scale forcing and local surface condition heterogeneity in Bergen. They revealed that emerging local breeze-like circulations strongly enhance the urban ventilation and dispersion of the air pollutants in situations with weak large-scale winds. Slightly stronger large-scale winds, however, can counteract these local recirculations, leading to enhanced surface air stagnation. Furthermore, this study looks at the concrete impact of the relative configuration of warmer water bodies in the city and the major transport corridor. We found that a relatively small local water body acted as a barrier for the horizontal transport of air pollutants from the largest street in the valley and along the valley bottom, transporting them vertically instead and hence diluting them. We found that the stable stratification accumulates the street-level pollution from the transport corridor in shallow air pockets near the surface. The polluted air pockets are transported by the local recirculations to other less polluted areas with only slow dilution. This combination of relatively long distance and complex transport paths together with weak dispersion is not sufficiently resolved in classical air pollution models. The findings have important implications for the air quality predictions over urban areas. Any prediction not resolving these, or similar local dynamic features, might not be able to correctly simulate the dispersion of pollutants in cities.


2011 ◽  
Vol 47 (9) ◽  
pp. 1197-1208 ◽  
Author(s):  
G. H. Yeoh ◽  
S. C. P. Cheung ◽  
J. Y. Tu ◽  
T. J. Barber

2019 ◽  
Vol 37 (4) ◽  
pp. 4409-4418 ◽  
Author(s):  
Min-min Zhou ◽  
John C. Parra-Álvarez ◽  
Philip J. Smith ◽  
Benjamin J. Isaac ◽  
Jeremy N. Thornock ◽  
...  

Author(s):  
Takashi Takata ◽  
Akira Yamaguchi ◽  
Masaaki Tanaka ◽  
Hiroyuki Ohshima

Turbulent statistics near a structural surface, such as a magnitude of temperature fluctuation and its frequency characteristic, play an important role in damage progression due to thermal stress. A Large Eddy Simulation (LES) has an advantage to obtain the turbulent statistics especially in terms of the frequency characteristic. However, it still needs a great number of computational cells near a wall. In the present paper, a two-layer approach based on boundary layer approximation is extended to an energy equation so that a low computational cost is achieved even in a large-scale LES analysis to obtain the near wall turbulent statistics. The numerical examinations are carried out based on a plane channel flow with constant heat generation. The friction Reynolds numbers (Reτ) of 395 and 10,000 are investigated, while the Prandtl number (Pr) is set to 0.71 in each analysis. It is demonstrated that the present method is cost-effective for a large-scale LES analysis.


2016 ◽  
Vol 139 (1) ◽  
Author(s):  
K. M. Nair ◽  
S. Sarkar

The primary objective is to perform a large eddy simulation (LES) using shear improved Smagorinsky model (SISM) to resolve the large-scale structures, which are primarily responsible for shear layer oscillations and acoustic loads in a cavity. The unsteady, three-dimensional (3D), compressible Navier–Stokes (N–S) equations have been solved following AUSM+-up algorithm in the finite-volume formulation for subsonic and supersonic flows, where the cavity length-to-depth ratio was 3.5 and the Reynolds number based on cavity depth was 42,000. The present LES resolves the formation of shear layer, its rollup resulting in large-scale structures apart from shock–shear layer interactions, and evolution of acoustic waves. It further indicates that hydrodynamic instability, rather than the acoustic waves, is the cause of self-sustained oscillation for subsonic flow, whereas the compressive and acoustic waves dictate the cavity oscillation, and thus the sound pressure level for supersonic flow. The present LES agrees well with the experimental data and is found to be accurate enough in resolving the shear layer growth, compressive wave structures, and radiated acoustic field.


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