We study the entrainment of water in air by a rotating wheel that is partially immersed on a fraction of its radius. The goal is the prediction of the nature of the spray of droplets around a car wheel fording (partnership with PSA-Peugeot Citroën). Preliminary studies concerned the case of a wheel rotating above a fixed bottom (pictures below). The emerging side of the wheel produces a meniscus which size increases with the rotation frequency. The fluid particle trajectories in this meniscus follow approximately a parabola. The meniscus behaves as a liquid sheet which atomisation leads to the formation of droplets which size is the thickness of the sheet. On the top of the wheel, a liquid film is entrained and it becomes quickly unstable into ligaments. These ligaments are stretched and they break into droplets that are ejected to the opposite side of the meniscus (instabilities of Rayleigh-Taylor and Rayleigh-Plateau). A new experiment has been designed and constructed in which the wheel rotates above a conveyor belt so that to study the effect of a mean flow on the rotating wheel.
