Turbulence of airflow matters in human thermophysiological response in the heat: The journal Temperature toolbox

Turbulent airflow is a fundamental characteristic of real-world outdoor and mechanically ventilated environments, yet most thermoregulation models rely on heat transfer coefficients derived from steady indoor airflows with low turbulence intensity. Using an updated Stolwijk thermoregulation model and a turbulence-informed heat transfer correlation, we evaluated the impact of turbulence intensity and integral length scale on human thermophysiological responses. Simulations were conducted across three environmental conditions (hot-dry, hot-humid, temperate), two clothing levels (0 and 0.6 clo), two activity levels (1.2 and 4.0 MET), and air speeds ranging from 0.4 to 5 m/s. Results show that turbulence significantly enhances convective and evaporative heat loss in temperate and hot-dry environments when unclothed. Compared to baseline simulations that neglect turbulence characteristics at equivalent air speed, core temperature differed by up to 0.3°C, and skin temperature by up to 1.8°C, highlighting the potential physiological relevance of turbulence. In contrast, the influence of turbulence is minimal in hot-humid environments and when clothed. These findings demonstrate that turbulence should not be viewed as inherently beneficial or detrimental, but rather as a mechanistic modifier of heat and mass transfer whose physiological impact depends on context, including ambient temperature, metabolic rate, clothing, and the skin-air temperature difference. This work advances the field by introducing a turbulence-resolved approach to support the improved assessment of heat exposure across vulnerable populations, including outdoor workers and athletes, and to guide the design of more effective cooling strategies and ventilation systems, such as fans, based on different climate and personal contexts.