Newsletter 2014.11 Index
Theme : "Mechanical Engineering Congress, 2014 Japan (MECJ-14) Part 1"
It is of great importance to investigate turbulent momentum and heat transfer at extremely high wind speeds in precisely predicting growth and development of tropical cyclones such as typhoons and hurricanes, as shown in Fig.1. Mass transfer is also important in estimating the effects of tropical cyclones on the global carbon cycle between atmosphere and oceans. In this study, turbulent momentum, heat and mass transfer across the wind-driven breaking air-water interface under strong wind conditions was experimentally investigated using a high-speed wind-wave tank shown in Fig.2. The results show that drag coefficient increases at low and moderate wind speeds with increasing U10 and becomes almost constant at high wind speeds. Sensible and latent heat transfer coefficients have almost constant values at low and moderate wind speeds and rapidly increase at high wind speeds. Mass transfer coefficient also rapidly increases with U∞ at high wind speeds. Our numerical simulation of a typhoon with our drag and heat transfer coefficients shows the bigger growth than a conventional simulation and also suggests the need for improving sub-models of cloud formation. The contribution of tropical cyclones to global CO2 transfer between atmosphere and oceans was estimated to be less than 20%. However, this contribution will depend on the future occurrence frequency of tropical cyclones.
Air-Water Interface, Turbulent Transport, Two-Phase Flow
Fig. 1 Sketch of momentum, heat and mass transfer in a typhoon.
Fig. 2 High-speed wind -wave tank.