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  第2回 CEISTセミナー

講師:Dr. Rudie Kunnen( Technical University of Eindhoven)


Collisions of cloud particles: numerical simulations and experiments

In cloud physics the growth of rain droplets is enhanced by turbulence.Turbulence increases the collision rate of droplets, leading to more coalescence events. This process is not well-understood in a quantitative sense. I will present our numerical and experimental approach to this problem.

In numerical simulations the usual point-particle approach is applied to constitute the droplet phase in a DNS of turbulent airflow in a windtunnel-like computational domain. Collision rates are evaluated in different sections of the spatially decaying turbulence.
Additionally, ellipsoids are also included in the calculations. These serve as a first-order approximation of solid ice crystals in clouds.

In experiments we produce a cloud of droplets in a turbulence box, driven by subwoofer speakers. This arrangement provides turbulence with good homogeneity and isotropy but with a zero mean flow. The droplets are tracked in time (3D-PTV) to obtain velocity statistics.
The next step will be to consider the measurement of droplet collisions, for which some ideas will be presented.

大西 領