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JAEA Reports

Local-scale high-resolution atmospheric dispersion model using large-eddy simulation; LOHDIM-LES

Nakayama, Hiromasa; Nagai, Haruyasu

JAEA-Data/Code 2015-026, 37 Pages, 2016/03

JAEA-Data-Code-2015-026.pdf:2.48MB

We developed LOcal-scale High-resolution atmospheric DIspersion Model using Large-Eddy Simulation (LOHDIM-LES). This dispersion model is designed based on LES which is effective to reproduce unsteady behaviors of turbulent flows and plume dispersion. The basic equations are the continuity equation, the Navier-Stokes equation, and the scalar conservation equation. Buildings and local terrain variability are resolved by high-resolution grids with of a few meters and these turbulent effects are represented by immersed boundary method. In simulating atmospheric turbulence, boundary layer flows are generated by a recycling turbulent inflow technique in a driver region set up at the upstream of the main analysis region. This turbulent inflow data are imposed at the inlet of the main analysis region. By this approach, the LOHDIM-LES can provide detailed information on wind velocities and plume concentration in the investigated area.

Oral presentation

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

Nakayama, Hiromasa; Takemi, Tetsuya*; Nagai, Haruyasu

no journal, , 

A significant amount of radioactive material was accidentally discharged into the atmosphere from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) from March 12, 2011. In conducting regional-scale atmospheric dispersion simulations, the nuclear emergency response system based on a meso-scale meteorological model (MM) was used. However, it is impossible to conduct detailed simulations of plume dispersion considering the turbulent effects in a local-scale because buildings, structures, and local terrain variability are not explicitly represented at high grid resolutions in those models. Therefore, an approach to couple an LES-based CFD model with a MM model should be promising. In this study, first we conduct LESs of plume dispersion around the FDNPP under a constant meteorological condition by prescribing constant mean wind velocities and directions at the inlet boundary condition, and then do them under a varying meteorological condition by coupling with a MM model. Our objective is to compare plume dispersion patterns under those different meteorological conditions and evaluate the effectiveness of the coupling computational method.

Oral presentation

Study on a generation method for LES thermally-stratified boundary layer flows using a recycling technique

Nakayama, Hiromasa; Takemi, Tetsuya*

no journal, , 

In using Large-Eddy Simulation (LES) in study fields of computational fluid engineering, boundary layer meteorology, and atmospheric dispersion, one of difficult problems is a treatment of turbulent inflow boundary. The variability of atmospheric flow is induced by meteorological disturbances, terrains, and surface roughness elements. Therefore, wind velocities are also always changed. In conducting LESs, time-dependent turbulent inflow data have to be imposed at the inlet boundary depending on the atmospheric conditions. In this study, from a practical application perspective, we propose a generation method for thermally-stratified boundary layer flows by a short fetch and discuss the effectiveness of the approach in comparison to the existing wind tunnel experimental data.

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