SootImage: An image recreation, post-processing validation procedure for sooting axisymmetric flames

Validation is a vital part of any computational fluid dynamics study. Validation is done by comparing the computed results to the experimental measurements performed in a known configuration. In sooting flames, such a comparison is non-trivial since the measurements have a wide range of uncertainty due to difficulties in directly measuring soot volume fractions. This work introduces a different way to verify the computations using a software package called SootImage. In this proposed methodology, comparisons are not made directly to the computed properties of interest (soot volume fraction and temperature). Instead, a post-processing procedure is performed to obtain an image of the flame based on the computed properties. This reconstructed image is compared to an actual image of the flame being studied. The algorithm of the image reconstruction utilized within SootImage is presented in detail. Finally, the usage of SootImage is demonstrated on a co-flowing, laminar ethylene/air diffusion flame. Program summary: Program Title: SootImage CPC Library link to program files: https://doi.org/10.17632/nc5myw64km.1 Developer's repository link: https://github.com/VictorChernov/SootImage Licensing provisions: CC BY NC 3.0 Programming language: MATLAB Nature of problem: The software allows comparing images of a real flame with the recreated image of a simulated flame. This requires two major steps. One is the recreation of the image of an axisymmetrical flame from the computed soot volume fraction and temperature fields for a known camera and optical configuration. The second is cropping and position images to obtain a meaningful comparison. Solution method: The solution recreates the image by integrating the soot thermal radiation over a line-of-sight. Soot is assumed to emit as gray body. The integrated radiation is passed through the color filters of the camera and is translated to pixel values. After the process is done for the whole flame, the width, height and origin of both flames are found, and images that can be easily compared are created.