Recently, there has been a trend in thermal power plants to adopt shorter stacks due to the shift to LNG as fuel. This has raised concerns about the potential impact of buildings and terrain on gas dispersion from these shorter stacks. Therefore, we proposed a calculation method based on Large Eddy Simulation (LES), which is expected to accurately reproduce unsteady flows around buildings and complex terrain. First, we investigated mesh resolution and grid shape requirements for accurately predicting stack downwash. Next, wind tunnel experiments were conducted in areas that include both buildings and terrain, in order to validate the developed model. The results demonstrated that the model can accurately predict ground-level concentrations. Based on these findings, we conclude that the proposed LES model is capable of reliably simulating exhaust gas dispersion in environments influenced by both buildings and terrain.

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In 2012, a tornado caused terrible damage in the Hojo district of Tsukuba City. In this study, tornado disaster preparedness in 1741 municipal regional disaster prevention plans across Japan was investigated. As a result, 90% of the 1,445 plans on the Web contained the word “tornado”. However, it became clear that only 381 plans described specific measures, and only a few plans described measures specific to tornado disasters. A visual survey of 279 buildings in Hojo district was conducted 11 years after the tornado disaster. The results indicated that approximately 30% of the buildings were demolished after the disaster. In particular, all buildings rated ‘High Wind Damage Rank 5’ were demolished; 64% of Rank 4 and 27% of Rank 3 buildings were also demolished. It is important to include measures specific to tornadoes, such as “understanding tornadoes” and “response immediately after a tornado,” in local disaster prevention plans throughout Japan.

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