Shape of an interface hit by an oblique jet

TL;DR

This paper investigates the shape and formation of cavities on a liquid surface caused by an oblique jet, combining experiments, simulations, and a theoretical model to understand the flow dynamics and cavity width.

Contribution

It introduces a new model linking flow detachment asymmetry, depression, and cavity width, supported by direct numerical simulations and experimental observations.

Findings

Cavity shape relates to a tilted fiber piercing the interface.

Flow detachment causes asymmetry and liquid acceleration beneath the surface.

The model predicts cavity width by balancing suction, weight, and surface tension.

Abstract

We report on the shape taken by the interface of a liquid bath when hit by a smooth oblique steady jet. When the angle between the jet and the bath decreases below $50^\circ$, a cavity is formed in front of the jet. In the inertial regime we explore, the jet boundary layer detaches in the impact region, thereby delimiting a core jet region outside of which the liquid is mainly in hydrostatic equilibrium. The shape of the outer meniscus is shown to be related to the one outside a tilted fiber piercing the fluid interface. In order to unravel the flow features and separation, we perform direct numerical simulations and show that the flow detachment displays an asymmetry, which results in the acceleration of the liquid below the surface, thereby creating a depression. With this observation, we propose a model balancing the suction force of this depression with the weight of the displaced water and the surface tension force to obtain a prediction for the typical width of the cavity.