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Sato, Takuto; Goger, B.*; Nakayama, Hiromasa
SOLA (Scientific Online Letters on the Atmosphere) (Internet), 21, p.17 - 23, 2025/01
Times Cited Count：0 Percentile：0.00(Meteorology & Atmospheric Sciences)In this study, we conducted large-eddy simulations of turbulent flows and plume dispersion over idealized two-dimensional double steep hills. In the simulations, we investigated the distribution patterns of the mean plume concentrations, considering various distances between the hills and emission sources. Our objective was to provide information on the area of influence of local hilly terrains on plume dispersion from the viewpoint of accuracy, i.e., determining if the conventional Gaussian plume model can accurately predict plume concentrations. The result showed that the clockwise circulation was dominant in the area between the windward and leeward hills (valley) when the valley width was less than 10 times the hill height (
). This circulation makes the flow close to the stack remain in the valley, resulting in the higher concentrations in the valley than in wider-valley (
10 valley) cases. The effect of the leeward hill on the flow field was negligible when the valley width was greater than 10. In the area beyond 20 from the crest of the windward hill, estimated plume spreads for all cases were similar, indicating that the area of influence of the hills was approximately 20.
Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Iimoto, Takeshi*
Atmosphere (Internet), 15(6), p.701_1 - 701_12, 2024/06
Times Cited Count：2 Percentile：59.73(Environmental Sciences)Building materials such as brick and concrete are known indoor radon (
Rn) and thoron (
Rn) sources. Most radon and thoron exhalation studies are based on the laboratory testing of pieces and blocks of such materials. To discuss if laboratory findings can be applied to a real-world environment, we conducted intensive in-situ exhalation tests on two solid concrete interior walls of an apartment in Japan for over a year. Exhalation rates of radon (
) and thoron (
) were measured by a measurement system, mainly consisting of an accumulation chamber and dedicated monitors. The indoor air temperature (
) and absolute humidity (
) were measured in parallel, and the wall-surface temperature and water content were occasionally measured. All data obtained here were investigated to reveal environmental and material-associated factors affecting exhalation from the concrete walls. There were weak correlations between or and T or at one tested wall, and moderate correlations of and strong correlations of with or at the other wall. Our findings on were consistent with those in a previous laboratory work where a concrete sample was subject to various temperatures, although a corresponding laboratory study of could not be collected. Additionally, moderate or strong correlation between and was observed for both tested walls. The comparison of the measured data and theoretical calculations revealed a new issue on how much impact each process of the emanation and migration within concrete pore spaces has on radon and thoron exhalation. This study provides an insight into parameterizing radon and thoron source inputs in modeling the spatiotemporal dynamics of indoor radon and thoron.
Sato, Takuto; Nakayama, Hiromasa
SOLA (Scientific Online Letters on the Atmosphere) (Internet), 20, p.371 - 377, 2024/00
Times Cited Count：0 Percentile：0.00(Meteorology & Atmospheric Sciences)Numerical simulations of convective boundary layers (CBLs) based on the stability categories of the Pasquill-Gifford (PG) chart were conducted using a large-eddy simulation (LES) model. We studied the simulation settings for different combinations of wind speeds and sensible heat fluxes that could quantitatively generate turbulences satisfying the requirement of each stability category. Additionally, we determined appropriate CBL depths for desired turbulence generation and verified the effectiveness of the velocity scale (
) in turbulence generation simulations. This study identified wind speed and sensible heat flux combinations that could generate turbulences under the atmospheric stability categories B (unstable), C (weakly unstable), and D (neutral). However, the results did not follow the scaling law based on in category D when the CBL depth was 600 m. A shallower CBL (300 m depth) should be set in category D to generate turbulence under the scaling law based on . In category B, the transient layer disappeared due to active thermals in the CBL when the depth was 300 m. These results indicated that we should set appropriate CBL depths in addition to horizontal wind speeds and sensible heat fluxes to generate desired and scalable turbulences based on the PG chart.
Nakayama, Hiromasa; Takemi, Tetsuya*; Yoshida, Toshiya
Atmosphere (Internet), 12(7), p.889_1 - 889_15, 2021/07
Times Cited Count：3 Percentile：13.26(Environmental Sciences)Contaminant gas dispersion within urban area resulting from accidental or intentional release is of great concern to public health and social security. When estimating plume dispersion in a built-up urban area under real meteorological conditions by computational fluid dynamics (CFD), a crucial issue is how to prescribe the model input conditions. There are typically two approaches: using the outputs of a meso-scale meteorological simulation (MMS) model and meteorological observations (OBS). However, the influence of the different approaches on the simulation results have not been fully demonstrated. In this study, we conducted large-eddy simulations (LESs) of plume dispersion in the urban central district under real meteorological conditions by coupling with a MMS model and OBS obtained at a single stationary point, and evaluated the two different coupling simulations in comparison with the field experimental data. The LES-MMS coupling showed better performance than the LES-OBS one. However, the latter one also showed a reasonable performance comparable to the acceptance criteria on the model prediction within a factor of two of the experimental data. These facts indicate that the approach of using observations at a single stationary point still has enough potential to drive CFD models for plume dispersion under real meteorological conditions.
Nakayama, Hiromasa; Yoshida, Toshiya; Terada, Hiroaki; Kadowaki, Masanao
Atmosphere (Internet), 12(7), p.899_1 - 899_16, 2021/07
Times Cited Count：1 Percentile：3.45(Environmental Sciences)In this study, first, we conducted meteorological observations by a Doppler LiDAR and simple plume release experiments by a mist spraying system at the site of Japan Atomic Energy Agency. Then, we developed a framework for prediction system of local-scale atmospheric dispersion based on a coupling of large-eddy simulation (LES) database and on-site meteorological observation. The LES-database was also created by pre-calculating high-resolution turbulent flows in the target site at mean wind directions of class interval. We provided the meteorological observed data with the LES database in consideration of building conditions and calculated three-dimensional distribution of the plume by a Lagrangian dispersion model. Compared to the instantaneous shot of the plume taken by a digital camera, it was shown that the mist plume transport direction was accurately simulated. It was concluded that our proposed framework for prediction system based on a coupling of LES-database and on-site meteorological observation is effective.
Inagaki, Atsushi*; Wangsaputra, Y.*; Kanda, Manabu*; Y
cel, M.*; Onodera, Naoyuki; Aoki, Takayuki*
SOLA (Scientific Online Letters on the Atmosphere) (Internet), 16, p.120 - 124, 2020/00
Times Cited Count：1 Percentile：2.99(Meteorology & Atmospheric Sciences)The similarity of the turbulence intensity profile with the inner-layer and the outer-layer scalings were examined for an urban boundary layer using numerical simulations. The simulations consider a developing neutral boundary layer over realistic building geometry. The computational domain covers an 19.2 km by 4.8 km and extends up to a height of 1 km with 2-m grids. Several turbulence intensity profiles are defined locally in the computational domain. The inner- and outer-layer scalings work well reducing the scatter of the turbulence intensity within the inner- and outer-layers, respectively, regardless of the surface geometry. Although the main scatters among the scaled profiles are attributed to the mismatch of the parts of the layer and the scaling parameters, their behaviors can also be explained by introducing a non-dimensional parameter which consists of the ratio of length or velocity.
