The impact of a water droplet on a stainless steel tube was studied using both numerical simul ations and experiments. A 3D numerical model of Bussmann et al. [I] for free-surface flows (such as an impacting droplet) was extended to include internal obstacles (such as a so lid tube) in the fluid computational domain. The results of the model were compared with experimental photographs for the impact of a 2 mm water droplet on two tube sizes: 3.18 mm (0.125 in) and 6.35 mm (0.25 in) O.D.; the impact velocity was 1 mls and 1.2 mls on the two tubes, respectively. The droplet impacting on the smaller tube size pinched off the tube surface. On the bigger tube size, however, surface tension effects arrested droplet downward flow on the tube surface; as a result, there was no droplet pinch off in this case. The good qualitative and quantitative agreement between the results of simulations and experimental photographs demonstrated the numerical model to be well suited for simulating free-surface flows over internal obstacles in general, and droplet spraying on tubes in particular.

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