# The circular capillary jump

## TL;DR

This paper investigates the surface-tension-driven hydraulic jump caused by a laminar liquid jet impact, demonstrating that a curvature singularity predicts the jump location, aligning with experimental data and ignoring gravity.

## Contribution

It introduces a surface-tension-based model predicting the hydraulic jump radius without considering gravity, matching experimental observations.

## Key findings

- The jump radius is independent of surface orientation.
- A singularity in film curvature predicts the jump location.
- Model predictions align with experimental measurements.

## Abstract

In this paper we re-examine the flow produced by the normal impact of a laminar liquid jet onto an infinite plane when the flow is dominated by surface tension. It is observed experimentally that after impact the liquid spreads radially over the plane away from the point of impact in a thin film. It is also observed that, at a finite radius, there is an abrupt increase in thickness of the film which has been identified as a hydraulic jump,and that this radius is independent of the orientation of the surface showing that gravity is unimportant (Bhagat et al. 2018). We show that the application of conservation of momentum in the film, subject only to viscosity and surface tension and ignoring gravity completely, predicts a singularity in the curvature of the liquid film and consequently a jump in the depth of the film at a finite radius. This location is almost identical to the radius of the jump predicted by conservation of energy and agrees with experimental observations