Large-scale Multiphase Large Eddy Simulation of Flow in Solid Rocket Motors

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.

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Comparative Large Eddy Simulation study of a large-scale buoyant fire

Heat and Mass Transfer ◽

10.1007/s00231-011-0771-2 ◽

2011 ◽

Vol 47 (9) ◽

pp. 1197-1208 ◽

Cited By ~ 1

Author(s):

G. H. Yeoh ◽

S. C. P. Cheung ◽

J. Y. Tu ◽

T. J. Barber

Keyword(s):

Large Eddy Simulation ◽

Simulation Study ◽

Large Scale ◽

Eddy Simulation ◽

Large Eddy

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Large-scale coherent structures of suspended dust concentration in the neutral atmospheric surface layer: A large-eddy simulation study

Physics of Fluids ◽

10.1063/1.5022089 ◽

2018 ◽

Vol 30 (4) ◽

pp. 046601 ◽

Cited By ~ 8

Author(s):

Yangyue Zhang ◽

Ruifeng Hu ◽

Xiaojing Zheng

Keyword(s):

Surface Layer ◽

Large Eddy Simulation ◽

Simulation Study ◽

Coherent Structures ◽

Large Scale ◽

Atmospheric Surface Layer ◽

Dust Concentration ◽

Eddy Simulation ◽

Large Eddy ◽

Suspended Dust

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Large-eddy simulation of ash deposition in a large-scale laboratory furnace

Proceedings of the Combustion Institute ◽

10.1016/j.proci.2018.09.034 ◽

2019 ◽

Vol 37 (4) ◽

pp. 4409-4418 ◽

Cited By ~ 16

Author(s):

Min-min Zhou ◽

John C. Parra-Álvarez ◽

Philip J. Smith ◽

Benjamin J. Isaac ◽

Jeremy N. Thornock ◽

...

Keyword(s):

Large Eddy Simulation ◽

Large Scale ◽

Ash Deposition ◽

Laboratory Furnace ◽

Eddy Simulation ◽

Large Eddy

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Application of Near Wall Model to Large Eddy Simulation Based on Boundary Layer Approximation

Volume 4: Computational Fluid Dynamics, Neutronics Methods and Coupled Codes; Student Paper Competition ◽

10.1115/icone14-89608 ◽

2006 ◽

Author(s):

Takashi Takata ◽

Akira Yamaguchi ◽

Masaaki Tanaka ◽

Hiroyuki Ohshima

Keyword(s):

Boundary Layer ◽

Large Eddy Simulation ◽

Frequency Characteristic ◽

Large Scale ◽

Plane Channel ◽

Boundary Layer Approximation ◽

Eddy Simulation ◽

Turbulent Statistics ◽

Large Eddy ◽

Near Wall

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.

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