Leidenfrost vapour layer moderation of the drag crisis and trajectories of superhydrophobic and hydrophilic spheres falling in water
Ivan U Vakarelski, Derek YC Chan, Sigurdur T Thoroddsen
Soft Matter | ROYAL SOC CHEMISTRY | Published : 2014
We investigate the dynamic effects of a Leidenfrost vapour layer sustained on the surface of heated steel spheres during free fall in water. We find that a stable vapour layer sustained on the textured superhydrophobic surface of spheres falling through 95 °C water can reduce the hydrodynamic drag by up to 75% and stabilize the sphere trajectory for the Reynolds number between 10(4) and 10(6), spanning the drag crisis in the absence of the vapour layer. For hydrophilic spheres under the same conditions, the transition to drag reduction and trajectory stability occurs abruptly at a temperature different from the static Leidenfrost point. The observed drag reduction effects are attributed to t..View full abstract
We acknowledge G. D. Li from the KAUST Solar and Photovoltaics Research Center for assisting in the water tank and heater device design, and the KAUST Machine Workshop for the support in setting the experiments. This work is support in part by an Australian Research Council Discovery Project Grant to DYCC.