Background oriented schlieren in a density stratified fluid

Abstract

Non-intrusive quantitative fluid density measurement methods are essential in the 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 extension to one of these methods, called background oriented schlieren, 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 multimedia 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 a non-intrusive full-field density measurements of transparent liquids.

A Miniature Intermittent-Flow Respirometry System with a 3D-Printed, Palm-Sized Zebrafish Treadmill for Measuring Rest and Activity Metabolic Rates

“…Fluorescent beads were introduced into the 3D-printed zebrafish treadmill, 2 to 9 V were applied to the DC motor with the 3D-printed propeller, and the movement of fluorescent beads was recorded using a high-speed video camera. The water velocities at the preset voltages were calculated using open-source PIV analysis software (OpenPIV) [ 30 ]. The water velocity showed a nearly linear relationship to the applied voltage ( Supplementary Figure S1 ), which enabled the provision of a temporary closed circulating water flow with flow velocities ranging from 0.1 to 20 cm/s.…”

OpenPIV-MATLAB — An open-source software for particle image velocimetry; test case: Birds’ aerodynamics

“…The POD toolbox was developed to extract energetic modes from velocity or vorticity fields to study coherent motions in turbulent flows [3,4]. Another OpenPIV toolbox extended the post-processing capabilities with calculation of the density fields using the background-oriented schlieren technique [5]. Most recently, we added a toolbox to estimate aero/hydrodynamic loads based on PIV data acquired in a body wake, entitled getWAKE [6].…”

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“…7a, b). Therefore we relied on a air/fresh-water/salt-water type calibration (Verso and Liberzon 2015) as explained in the next section. Finally, the refractive index gradient is related to the density gradient through…”