Assessment of some experimental and image analysis factors for background oriented schlieren measurements

TL;DR

This study evaluates how various experimental and image analysis factors influence the accuracy of background oriented schlieren measurements for fluid flow, highlighting the importance of image quality and analysis parameters.

Contribution

It systematically investigates the effects of image sensor quality and analysis parameters on BOS measurement accuracy, providing guidelines for improved fluid flow visualization.

Findings

Image quality significantly affects measurement accuracy.

Interrogation window size impacts vector shift evaluation.

BOS effectively measures natural convection cooling, matching thermocouple data.

Abstract

Quantitative measurements of fluid flow properties can be achieved by background oriented schlieren. In this paper it is shown that this depends on several factors. Image quality index is used to investigate the influence of the image sensor and the quality of its output. Image evaluation is applied to synthetic images which are treated with a step function, so that they simulate the sharp density jump. The gradual change of the evaluated vector shift revealed the major dependence on the interrogation window, and less so on the background features. BOS applied to shock wave reflection from a wedge in a shock tube gave qualitative results, due to large uncertainties. But, the application to cooling by natural convection gave satisfactory results, comparable to thermocouple data and theory.