単純住宅モデルを対象とした変動気流場における室内外通風性状の解析 LES(Large-Eddy Simulation)による住宅の自然換気•通風性状に関する研究 その1

摘要

建物の自然換気•通風性能の評価に関する研究では、外部風の時間的変動を考盧した実現象により近い実験•解析手法で評価することが期待されている。既往研究では主にReynolds Averaged Navier-Stokes Simulation(RANS)を用いた数値流体解析 (CFD) が行われ、時間的変化が均されたアンサンブル平均値によって室内流入風速や室内の風速比分布、通風量等の通風気流性状が明らかにされている。しかし実現象では、外部風は絶えず変動し、それに応じて室内の通風気流の速度分布も変化するため、瞬時的な通風性状を把握するためには時間的変動を解析できるRANSモデル以外の解析手法を用いることが望ましい。%Natural cross ventilation in house is commonly used as ventilation method in Japan. It is influenced by wind direction, distribution of wind velocity and total pressure on walls. Cross ventilation is not observed with using Reynolds Averaged Navier-Stokes Simulation (RANS), nevertheless occurs in actual phenomena. Flow field in the house varies depending on fluctuating wind. For example, cross ventilation is affected by the wind turbulence around the house, in case of two openings positioned symmetrically on opposite walls parallel to wind direction. Therefore, replicating actual phenomena with using CFD is very important to provide evaluation method for ventilation design. Recently, unsteady fluid flow phenomena are analyzed using Large-Eddy Simulation (LES). In this study, opening conditions and wind direction are calculation variables, five cross ventilated simple house models are calculated using LES. Distributions of instantaneous wind speed ratio and pressure, mean wind speed ratio about cross-ventilated houses are reported. In opening conditions that time-averaged inflow is not observed, instantaneous inflow caused by pressure difference on the walls is generated by turns at each opening. Unsteady cross ventilation is replicated with using LES under opening conditions that obtain no-ventilation in steady-state flow field.