| 内容提要: |
Natural ventilation can improve indoor air quality, potentially reduce energy consumption, and provide a high level of thermal comfort for occupants. With the development of computing resources and grid generation techniques, an increasing number of researchers have used computational fluid dynamics to design naturally ventilated buildings. To design naturally ventilated buildings, the first step is to obtain reliable meteorological wind information, such as wind speed and wind direction.
Previous investigations generally used hourly wind speed and direction obtained from a meteorological station as inflow boundary conditions. This is because a meteorological station typically provides hourly data. However, in reality, cross ventilation should be determined minute by minute or even second by second. Appropriate wind information within an hour-long period is prerequisite for obtaining rational wind flow fields, and then the cross-ventilation rate. However, previous studies have not correctly considered the transient characteristics of the wind. Therefore, it is important to explore how to correctly obtain the unsteady inflow boundary conditions.
This investigation proposed a correlation method to convert hour-by-hour into minute-by-minute or even second-by-second by using the unsteady wind information from the building rooftop. With the unsteady wind information, we used the CFD modeling method to calculate the natural ventilation rate through an apartment for a period of time. In order to validate our method, this investigation measured the wind speed on a building rooftop and the cross-natural-ventilation rate through an apartment in Tianjin, China. Our investigation found that the simulated wind speed with the measured data on the rooftop of the apartment building. The simulated results agreed well with the measured data. The mean relative error between the numerical results and the experimental data was 24.4%.We also conducted conventional steady CFD simulation to calculate the cross ventilation. The corresponding air change rate in the apartment would be 5.3 ACH, which was calculated as the simulated volumetric flow rate through the apartment over the apartment volume. The steady CFD simulation significantly overestimated the air change rate, by a factor of two, which is unacceptable. |