Moiré tomography for the diagnoses of flow fields with consideration of ray propagation

Abstract

Abstract Moire tomography has been considered as powerful diagnostic tool to flow fields with advantages of noncontact, compact optical structure, strong anti-vibration capability and large dynamic range. However, the refractive index reconstructions in the existing moire tomography are based on the straight ray assumption, by which the light propagation effects caused by the inhomogeneities of flow fields are not taken into account. In this paper, a spatial-domain filtered back-propagation (FBPP) algorithm for moire tomography is studied from the wave equation in inhomogeneous media. Three advancements can be achieved by the algorithm: (1) the weak scattering effect caused by the inhomogeneities of flow field is considered; (2) the first-order derivative of the projected phase measured by moire deflectometry can be directly employed to quantitatively reconstruct the refractive index; (3) the reconstruction is calculated in pure spatial domain, which can reduce the errors resulted by the conversions in frequency domain in the conventional FBPP algorithm. The feasibility and accuracy of the algorithm is checked by numerical simulations. Finally, the refractive index of an axisymmetric propane-air premixed flame is measured by moire tomography with the proposed reconstruction algorithm and the temperature distribution is deduced.