自然換気制御のための建物屋上近傍気流の風速モニタリング位置に関する研究

抄録

Mid- to high-rise buildings are often provided with a 2-D anemometer on the roof top. The measured data of external wind is not only to be stored into BEMS data, but available for control of building operation as well, such as natural ventilation (NV). However, both velocity and direction around the roof top could significantly depend on location due to the flow separation and vortex, and it becomes difficult to determine the position of the anemometer. Therefore, the authors first aim to arrange basic data regarding horizontal distribution of wind velocity and direction above the building. For this purpose, in this paper, velocity fields are analyzed focusing on the vicinity of the roof top while changing external wind direction. Regarding the CFD analysis, the Large Eddy Simulation (LES), is used to investigate instantaneous velocity fields. As the first step, probability density of difference between monitored and actual wind direction were examined by LES and wind tunnel experiment. It was shown that at the low position the monitored direction differed from actual external wind direction i.e., when θ = 0° and 22.5° and measurement accuracy of direction is high if the measurement height is high as shown in Fig. 6 and Fig. 7. Second, by comparing probability of dimensionless velocity, it was indicated that wind velocity is low in separation area, and accuracy of measurement is often high when θ = 45° as shown in Fig. 10 and Fig. 11.

 

The conclusions obtained in this paper are summarized as follows.

(1) The probability of monitoring the same wind direction as that of external wind direction was compared at different points above roof top. In most of the cases, the higher the measurement position was, the higher the probability was. The measurement accuracy was particularly low at the lower section on the leeward except when θ = 45°. On the other hand, when θ= 45°, the measurement accuracy is high in most of the cases regardless of the measurement positions.

(2) When only one 2-D anemometer was installed at the center of roof top, the ideal height would be at Y = 0.2L (L is the plane dimension of building model). When an anemometer was installed at Y = 0.1L, the measurement accuracy would be higher when installed at the corner than at the center.

(3) When θ = 0°, the monitoring wind velocity was lower than that of external wind at lower section in most of the cases. However, when θ = 45°, monitored velocity was almost the same as that of external wind but at θ = 45°, regardless of the measurement height. When θ = 22.5°, the flow characteristic was the combination of θ = 0° and 45°. The decrease of wind velocity caused by separation flow at side AB was relatively small, while there existed weak wind region at side AD, as well as θ = 0°.

 

As a future prospect, by providing the reliable monitoring method of external wind direction and velocity, the proposal of advanced control for NV such as real-time control of openings, adjusting the opening condition of selected openings, is expected. Additionally, in order to choose the appropriate measurement position, more data need to be accumulated, under many conditions such as building shapes and surrounding buildings.