Abstract
The presence of ambient air in liquid-slamming events plays a crucial role in influencing the shape of the liquid surface prior to the impact, and the distribution of loads created upon impact. We study the effect of trapped air on impact loads in a simplified geometry, by slamming a horizontal flat disc onto a stationary water bath at a well-controlled velocity. We show how air trapping influences pressure peaks at different radial locations on the disc, how the pressure impulses are affected and how local pressure impulses differ from those obtained from area-integrated (force) impulses at impact. More specifically, we find that the air layer causes a gradual buildup of the load before the peak value is reached, and show that this buildup follows inertial scaling. Further, the same localised pressure impulse at the disc centre is found to be lower than the corresponding (area-integrated) force impulse on the entire disc. While the (area-integrated) force impulses are close to the classical result of Batchelor (An Introduction to Fluid Dynamics, Cambridge University Press, 1967, § 6.10) and Glasheen & McMahon (Phys. Fluids, vol. 8, issue 8, 1996, pp. 2078–2083), the localised pressure impulses at the disc centre, where the trapped air layer is at its thickest, lie closer to the theoretical estimation by Peterset al.(J. Fluid Mech., vol. 724, 2013, pp. 553–580) for an air-cushioned impact.
Highlights
Situations involving the impact of a liquid on solid, or vice versa are commonly found in industrial applications
We report here experiments where a flat disc is impacting at a controlled, constant velocity on a deep water bath initially at rest
The first pressure peak is registered at the disc edge, where the disc makes first contact with the liquid
Summary
Situations involving the impact of a liquid on solid, or vice versa are commonly found in industrial applications. In all situations, the surrounding air can have a very non-trivial influence on the generated load, and its distribution on the solid structure (Bogaert et al 2010; Dias & Ghidaglia 2018) One way this occurs is via aeration of the liquid phase (Bredmose, Bullock & Hogg 2015; Ma et al 2016). The peak values of both are found to be very sensitive to the temporal resolution of the equipment, something that is known from the liquid-slamming literature over decades This is connected to the fact that theoretically, in the absence of air cushioning, the moment of impact creates a temporal pressure singularity at the point of contact on the solid. Turning to the impulse accumulated during the impact peak, the (area-integrated) force impulses are found to lie very close to the classical result of Batchelor (1967, § 6.10) and Glasheen & McMahon (1996), while the local pressure impulses at the disc centre lie along the air-cushioned impact impulse calculation of Peters, van der Meer & Gordillo (2013)
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