Large‐eddy simulation of urban boundary‐layer flows by generating turbulent inflows from mesoscale meteorological simulations

Nakayama, Hiromasa; Takemi, Tetsuya; Nagai, Hiroki

doi:10.1002/asl.377

Cited by 68 publications

(51 citation statements)

References 11 publications

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“…H s over land was chosen as −0.025 K m s −1 , corresponding to approximately 25 W m −2 . This is in agreement with heat fluxes found from observational studies (Brümmer and Schultze, 2015;Nordbo et al, 2012). In addition to the cases with mixed BC, we also simulated a test case with a constant H s of 0 K m s −1 over the entire domain, representing a situation with neutral stratification.…”

Section: Numerical Experimentssupporting

confidence: 85%

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Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

Wolf¹,

Esau²,

Reuder

2017

Atmos. Chem. Phys.

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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 NO 2 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 largescale 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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Section: Numerical Experimentssupporting

confidence: 85%

“…One could name a few relevant urban studies. For example, Letzel et al (2008) and Nakayama et al (2012) simulated the flow on the neighbourhood-scale in Tokyo, Japan. Esau (2012) studied the dispersion of a passive tracer over central Paris, France.…”

mentioning

confidence: 99%

Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

Wolf¹,

Esau²,

Reuder

2017

Atmos. Chem. Phys.

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“…LETZEL et al (2008). (2008) and NAKAYAMA et al (2012) is beyond the scope of this case study. We attempt to use one average roughness length for the entire upstream area.…”

Section: Hamburg Case Studymentioning

confidence: 99%

The effect of unsteady and baroclinic forcing on predicted wind profiles in Large Eddy Simulations: Two case studies of the daytime atmospheric boundary layer

Pedersen¹,

Kelly²,

Gryning³

et al. 2013

metz

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“…Therefore, first, we proposed the treatment of the inflow boundary conditions in order to automatically input wind velocity data obtained by the MM model into the LES model under neutral stability conditions, depending on mean wind directions in the meteorological field (Nakayama et al, 2012(Nakayama et al, , 2015. Figure 1 shows a schematic diagram of the treatment of inflow boundary conditions in the LES model.…”

Section: Generation Of Turbulent Inflows From MM Outputsmentioning

confidence: 99%

Large-eddy simulation of turbulent winds during the Fukushima Daiichi Nuclear Power Plant accident by coupling with a meso-scale meteorological simulation model

2015

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Abstract. A significant amount of radioactive material was accidentally discharged into the atmosphere from the Fukushima Dai-ichi Nuclear Power Plant from 12 March 2011, which produced high contaminated areas over a wide region in Japan. In conducting regional-scale atmospheric dispersion simulations, the computerbased nuclear emergency response system WSPEEDI-II developed by Japan Atomic Energy Agency was used. Because this system is driven by a meso-scale meteorological (MM) model, it is difficult to reproduce smallscale wind fluctuations due to the effects of local terrain variability and buildings within a nuclear facility that are not explicitly represented in MM models. In this study, we propose a computational approach to couple an LES-based CFD model with a MM model for detailed simulations of turbulent winds with buoyancy effects under real meteorological conditions using turbulent inflow technique. Compared to the simple measurement data, especially, the 10 min averaged wind directions of the LES differ by more than 30 degrees during some period of time. However, distribution patterns of wind speeds, directions, and potential temperature are similar to the MM data. This implies that our coupling technique has potential performance to provide detailed data on contaminated area in the nuclear accidents.

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Large‐eddy simulation of urban boundary‐layer flows by generating turbulent inflows from mesoscale meteorological simulations

Cited by 68 publications

References 11 publications

Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

The effect of unsteady and baroclinic forcing on predicted wind profiles in Large Eddy Simulations: Two case studies of the daytime atmospheric boundary layer

Large-eddy simulation of turbulent winds during the Fukushima Daiichi Nuclear Power Plant accident by coupling with a meso-scale meteorological simulation model

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