A bent straw as a tool for an affordable student-safe experiment in vortex ring dynamics

TL;DR

This paper introduces an affordable, student-safe experiment using a bent straw and dyed water to generate and study vortex rings, making complex fluid dynamics accessible for educational purposes.

Contribution

It presents a simple, low-cost method for visualizing and analyzing vortex ring dynamics suitable for undergraduate education.

Findings

Vortex rings produced mimic seminal experiments with secondary structures.

Asymmetric vortex rings demonstrated using nonplanar and triangular jet exits.

Experiment allows control of key parameters and can be imaged with a smartphone.

Abstract

Vortex dynamics are an important topic in fluid dynamics, explaining phenomena like drag and lift generation, jet propulsion, and corner flows. It is also often excluded from introductory or undergraduate fluid dynamics courses on account of its complexity and the inaccessibility of practical and engaging experiments. We present an affordable student-safe experiment to generate vortex rings and study their dynamics using a bent straw and dyed water that allows students to control key parameters, can be imaged using a smartphone camera, and explains the complex physics with simple and easily measured parameters. Vortex rings are produced that parallel seminal experiments, demonstrating secondary structures and the mirroring effect. Meanwhile, nonplanar and triangular jet exits are used to demonstrate asymmetric vortex rings and vortex ring inversion.