Human body convective heat transfer coefficient under non-stationary turbulent wind

Abstract

In recent decades, extensive research has focused on the role of dynamic airflow in improving thermal comfort from both physiological and psychological perspectives. However, the specific mechanism by which dynamic airflow affects convective heat transfer from the human body remains unclear. This study utilizes an active shutter and a passive grid to simulate non-stationary turbulent flows in a wind tunnel, and employs a thermal manikin to determine the convective heat transfer coefficient (h<inf>c</inf>) over the human body. Considering the physical constraints posed by a wind tunnel, the simulated wind conditions were considered to be reasonably representative of pedestrian-level wind environment. The findings indicate that while high-frequency turbulence intensity significantly increases h<inf>c</inf>, h<inf>c</inf> does not change notably with fluctuation amplitude in the low-frequency range. In outdoor settings, turbulence intensity can be overestimated by more than half if the synoptic trend is not removed. Therefore, detrending dynamic flow is critical for accurately calculating turbulence intensity; otherwise, the whole body's h<inf>c</inf> could be overestimated by up to 40 %. Furthermore, when the integral length scale is smaller than half the manikin's characteristic length, the impact on h<inf>c</inf> is limited. A reduction in wavelength of low-frequency fluctuation component in dynamic flow contributes to enhancing h<inf>c</inf>, while no more than 4 % in typical outdoor pedestrian-level wind conditions. To improve the accuracy of the predicted h<inf>c</inf> in prototype pedestrian-level urban environment, an equivalent wind speed which accounts for the effects of turbulence has been proposed to adjust the wind speed input in current thermal comfort models.