Pocket Schlieren: a background oriented schlieren imaging platform on a smartphone

TL;DR

Pocket Schlieren transforms flow visualization by enabling smartphone-based background-oriented schlieren imaging, making the technique accessible for scientific and educational use without specialized equipment.

Contribution

This work introduces a smartphone platform for BOS, utilizing algorithms like CFS and OF, to democratize flow visualization and analysis.

Findings

Successfully visualized various flames and heat sources.

Operates on both engineered and natural backgrounds.

Available publicly for educational and scientific use.

Abstract

Background-oriented schlieren (BOS) is a powerful technique for flow visualization. Nevertheless, the widespread dissemination of BOS is impeded by its dependence on scientific cameras, computing hardware, and dedicated analysis software. In this work, we aim to democratize BOS by providing a smartphone based scientific tool called "Pocket Schlieren". Pocket Schlieren enables users to directly capture, process, and visualize flow phenomena on their smartphones. The underlying algorithm incorporates consecutive frame subtraction (CFS) and optical flow (OF) techniques to compute the density gradients inside a flow. It performs on both engineered and natural background patterns. Using Pocket Schlieren, we successfully visualized the flow produced from a burning candle flame, butane lighter, hot soldering iron, room heater, water immersion heating rod, and a large outdoor butane flame. Pocket Schlieren promises to serve as a frugal yet potent instrument for scientific and educational purposes. We have made it publicly available at doi: 10.5281/zenodo.10949271.