Analysis of limitations of tomographic BOS measurements in a lean H2-air premixed flame

Background Oriented Schlieren (BOS) is an optical technique that visualizes and quantifies refractive index gradients in transparent media, used extensively in studying compressible flows, heat transfer, and combustion. The refractive index field can be converted to a density field using the Lorentz-Lorenz or Gladstone-Dale equations. Recently, the tomographic version of BOS has gained attention for its application in these fields. Sipkens et al. proposed the ARAP method for tomographic BOS, which improves reconstruction accuracy by accounting for light rays converging at the camera pinhole, a common setup with entocentric lenses. This study aims to assess the limitations of tomographic BOS reconstruction using numerical simulations of an axisymmetric hydrogen Bunsen flame, comparing the results with experimental BOS measurements. It has been observed that the constant composition assumption (i.e., assuming a unique value of the Gladstone-Dale constant independently from composition) may introduce some limited errors, whereas the implementation of the ARAP algorithm has a negligible impact on the computation of temperature distribution.