Effect of incident laser sheet orientation on the OH-PLIF imaging of detonations

Abstract

This study aims to investigate the effect of laser sheet orientation on the OH-planar laser-induced fluorescence (OH-PLIF) imaging of a detonation wave and to identify the potential benefit of using a transverse laser orientation, compared to the conventional frontal orientation. In this study, we developed a new laser-induced fluorescence (LIF) model, based on a preexisting one, to include a more fundamental calculation of the absorption lineshape and the effects of the laser orientation on the fluorescence signal. One- and two-dimensional simulations are used to validate this new LIF model for both laser orientations using OH-PLIF images from the literature. The effect of the two laser orientations on detonation imaging is investigated numerically on a two-dimensional OH field. Based on these results, the frontal orientation seems more suitable to collect information near the detonation front, while the transverse laser orientation can give more quantitative information far from the front and only for short optical paths. With the present laser configuration and experimental conditions, both laser orientations present the same limitation with a strong laser energy absorption for long optical paths. While these first results show a qualitative agreement with experimental data, new experimental data are required to quantitatively validate this promising transverse laser orientation and confirm its relevance for OH-PLIF imaging of detonations.