A Dual-sided PLIF40 Method to Mitigate the Impact of Total Reflection in Liquid Film Imaging

Planar Laser-Induced Fluorescence (PLIF) has been widely applied in the investigation of annular flow. However, it faced impediments due to the imaging distortions from the curvature of the pipe wall and the fluctuations at the gas-liquid interface. In this paper, the influence of circumferential waves on PLIF40 imaging is examined. Employing optical path analysis, the influence of pipe wall curvature is corrected. Numerical calculations are utilized to scrutinize the total internal reflection induced by circumferential fluctuations with varying amplitudes and liquid film thicknesses. The results indicate that the underestimating liquid film thickness in traditional PLIF90, stemming from light occlusion, has the negligible effects on PLIF40. Furthermore, considering the uneven distribution of the fluctuations at the gas-liquid interface, a dual-sided PLIF40 method is proposed to mitigate the impact of total internal reflection. Numerical calculations and experiments are conducted to validate the effectiveness of the method. And the analysis demonstrates the notable performance of dual-sided PLIF40 in suppressing total reflection and recovering the transient flow field.