A study of evaluation method of the concentration variance at the subgrid-scale in large-eddy simulation: Development of prediction system for micro-scale atmospheric pollution Part 4

We conducted an experiment and large-eddy simulation (LES) of the dispersion of an inert gas in a test chamber which modeled the urban street canyon. In LES, the subgrid-scale variance (SGSV) of the pollutant concentration is omitted by the filtering operation. To evaluate it, we introduced a transport equation of SGSV and solved it with other governing equations. Concentration fluctuations which accounted SGSV showed good agreement with results in the experiment except the near-source region. A budget analysis of the transport equation found the local non-equilibriums of SGSV and difficulty of the zero-equation formulation of SGSV in the canyon.