A study of the characteristics of dynamic incoming flow directions of different airflows and their influence on wind comfort

Studies on the dynamic characteristics and comfort evaluation of natural and mechanical wind have been extensively conducted over the past two decades. However, in these contributions, varying wind directions were not considered. In this study, we systematically analysed different airflows from the perspective of the wind azimuth by using statistical analysis, power spectral analysis, wavelet analysis and chaos analysis. Several concepts are newly defined, such as the wind azimuth fluctuation rate (WAFR), the wind azimuth power spectral exponent (beta(a) value) and the dimensionless parameter of the phase space curve (delta(a) value). The results show that the standard deviations (SDs) of the wind azimuth, WAFR, and beta(a) values of typical natural wind are typically larger than those of mechanical wind, while the delta(a) value is lower. The differences in the direction characteristics between natural and mechanical wind highly agree with those in the velocity characteristics. To determine how the direction influences wind comfort, seventeen human subjects were invited to participate in a mixed experiment and exposed to five types of airflow. The results show that true natural wind was preferred, which may be due to the frequently changing direction. The findings also reveal that both the velocity and direction characteristics significantly influence wind comfort evaluations. By understanding the dynamic wind direction characteristics of airflows, this paper may provide new insights into further studies on characteristics, comfort assessments and the application of dynamic wind field in indoor built environments.