Synthetic Schlieren -- application to the visualization and characterization of air convection

TL;DR

Synthetic schlieren is an accessible optical method that visualizes and characterizes air convection flows, revealing phenomena invisible to the naked eye and linking flow velocity to surface temperature.

Contribution

This paper presents a simple, affordable implementation of synthetic schlieren for visualizing air convection and demonstrates its ability to relate flow velocity to surface temperature.

Findings

Convection plume velocity correlates with surface temperature.

The method visualizes invisible air flows like rising plumes from a hand.

It offers an educational tool for demonstrating fluid dynamics.

Abstract

Synthetic schlieren is an digital image processing optical method relying on the variation of optical index to visualize the flow of a transparent fluid. In this article, we present a step-by step, easy-to-implement and affordable experimental realization of this technique. The method is applied to air convection caused by a warm surface. We show that the velocity of rising convection plumes can be linked to the temperature of the warm surface and propose a simple physical argument to explain this dependence. Moreover, using this method, one can reveal the tenuous convection plumes rising from ounce's hand, a phenomenon invisible to the naked eye. This spectacular result may help student realize the power of careful data acquisition combined with astute image processing techniques.