Background Oriented Schlieren in a Density Stratified Fluid

TL;DR

This paper extends the Background Oriented Schlieren method to accurately measure density fields in stratified liquids, overcoming optical aberrations caused by multi-media imaging.

Contribution

The study introduces a calibration and image remapping technique that corrects stratified media distortions in BOS, enabling precise non-intrusive density measurements.

Findings

Successful correction of optical aberrations in stratified media

Accurate density field reconstructions demonstrated

Method applicable to transparent liquid experiments

Abstract

Non-intrusive quantitative fluid density measurements methods are essential in stratified flow experiments. Digital imaging leads to synthetic Schlieren methods in which the variations of the index of refraction are reconstructed computationally. In this study, an important extension to one of these methods, called Background Oriented Schlieren (BOS), is proposed. The extension enables an accurate reconstruction of the density field in stratified liquid experiments. Typically, the experiments are performed by the light source, background pattern, and the camera positioned on the opposite sides of a transparent vessel. The multi-media imaging through air-glass-water-glass-air leads to an additional aberration that destroys the reconstruction. A two-step calibration and image remapping transform are the key components that correct the images through the stratified media and provide non-intrusive full-field density measurements of transparent liquids.