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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.
Sato, Takuto; Nakayama, Hiromasa
SOLA (Scientific Online Letters on the Atmosphere) (Internet), 20, p.371 - 377, 2024/00
Times Cited Count：1 Percentile：9.67(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.
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：2.55(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.
