Establishment of high-precision model for ventilation flow rate and proposal of natural ventilation design method

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Ventilation is a phenomenon of complicated turbulent flow, which exhibits reversible and irreversible changes of energy between dynamic pressure and static pressure associated with extreme deformation of airflows near openings. The wind tunnel experiment and numerical analyses have been carried out.The findings of the study can be summarized as follows.(1)The primary cause of the inflow downfall at inflow opening lies in the pressure gradient due to the re-circulation at the lower portion of the windward surface.(2)The defects of the model characteristic to the standard k.-ε.model could be improved to a certain extent by application of the modified models. On the other hand, when LES is used, the factors such as wind pressure coefficient, turbulence energy, etc. are more accurately reproduced than k-εtype models.(3)To elucidate the mechanism of total pressure loss, the shape of a virtual flow tube passing through the inflow opening was calculated by tracing the trajectories of passive … More markers. The flow passing through the opening changes to a complicated flow where acceleration and deceleration occur within short distance. When the wind direction is other than 0℃, the stream tube contacts the wall surface before it reaches the opening. When the wind direction is set to 67.5°, the stream tube changes to a flow along the wall surface and then reaches the opening.(4)The total pressure at the opening is constant until the wind direction reaches 45℃, When the wind direction exceeds 45℃, the airflow separates at the windward corner, and the total pressure greatly decreases.(5)The proposed local dynamic similarity model could predict the ventilation flow rate with better accuracy than the conventional orifice model when discharge coefficients decreased due to changes of wind directions.(6)The simplified method using a single wire type hot-wire anemometer could roughly estimate total pressure at the opening for an inflow surface if the dynamic pressure of velocity parallel to the wall at a point away by one-tenth of building height was added to the wind pressure. Less