Development of local-scale high-resolution atmospheric dispersion model using large-eddy simulation. Part 4: turbulent flows and plume dispersion in an actual urban area

Abstract

We have developed a local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) to assess the safety at nuclear facilities and to respond to emergency situations resulting from accidental or deliberate releases of radioactive materials (e.g., a terrorist attack in an urban area). In Part 1, the unsteady behavior of a plume dispersing over a flat terrain was successfully simulated. In Parts 2 and 3, LESs of turbulent flows and plume dispersion around an isolated building and in building arrays with different obstacle densities were performed, which showed the basic performance comparable to wind tunnel experimental technique. In this study, we apply the LES model to turbulent flows and plume dispersion in an actual urban area. Although some of the turbulence and dispersion characteristics are quantitatively different from the wind tunnel experimental data, the distribution patterns are generally similar to those of the experiments. It is concluded that our LES model simulates reasonably the unsteady behavior of turbulent flows and plume dispersion even for complex heterogeneous urban areas.

Development ofLOcal-scaleHigh-resolution atmosphericDIspersionModel usingLarge-EddySimulation. Part 5: detailed simulation of turbulent flows and plume dispersion in an actual urban area under real meteorological conditions

“…The building effect is incorporated into the Navier-Stokes equation as an external force represented by the immersed boundary method proposed by Goldstein et al [16]. The validity of this method was shown from the previous LES studies of complex turbulent flows in various surface geometries [6,8,9]. The subgrid-scale turbulent effect is represented by the standard Smagorinsky model [17] with a constant value of 0.1.…”

“…The subgrid-scale scalar flux is also parameterized by an eddy viscosity model. The turbulent Schmidt number is set to 0.5 because this constant value is applicable to plume dispersion over a flat terrain [5], around an isolated building [6], over a two-dimensional hill [7], in building arrays with various obstacle densities [8], and within an actual urban area [9]. Information on the computational code such as the coupling algorithm of the velocity and pressure fields, the Poisson equation for pressure, and the spatial discretization in the basic equation is provided in part 1 -4 of this paper series.…”

“…Furthermore, LES models have potential performance to provide accurate data of turbulent flows and plume dispersion comparable to wind tunnel experiments. Therefore, we have developed the L Ocal-scale High-resolution atmospheric DIspersion Model using Large-Eddy Simulation (LOHDIM-LES) and investigated the basic performance in comparison to wind tunnel experiments of turbulent flows and plume dispersion over a flat terrain and a two-dimensional hill, around an isolated building, within building arrays with different obstacle densities, and within a central district of an actual urban area [5][6][7][8][9].…”

Large-eddy simulation of plume dispersion under various thermally stratified boundary layers

“…Basu et al (2008) conducted LESs of a diurnally varying atmospheric boundary layer and mentioned that the static type of SGS model doesn't reproduce a clear low-level jet in the nighttime although no significant differences between the static and dynamic type of models are found in the daytime. On the other hand, we have performed LESs of turbulent flows over a two-dimensional hill (Nakayama and Nagai, 2010), in building arrays with different obstacle densities (Nakayama et al, 2013), and in an actual urban area (Nakayama et al, 2014), and showed that the standard Smagorinsky model can produce reasonable results in comparison to wind tunnel experimental data. Therefore, the standard Smagorinsky model is used in our LES model because of its wide applicability to various environmental flows.…”

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

“…The model used for local-scale detailed simulations is the LOHDIM-LES developed by Nakayama et al (2014). The basic equations are the filtered continuity, Navier-Stokes, and temperature transport equations under the Boussinesq approximation.…”