Two-phase PIV method using two excitation and two emission spectra

To be able to characterize the airflow in the presence of liquid droplets in a confined geometry, a new two-phase particle image velocimetry (PIV) method is developed. It is based on a two-colour YAG laser and two different fluorescent dyes dissolved in the gas-phase tracers and droplets. This approach permits to separate the images (and thus the information) of the two phases optically and simultaneously. When experiments need to be carried out in a confined geometry (such as in a wind tunnel) with uniform droplet distribution and high turbulence, which are the case in the present investigation, one should be able to deal with continuous droplet deposition on the lateral walls through which the cameras acquire images. It requires the adaptation of the experimental conditions and the development of a dynamic background subtraction algorithm. The typical results reveal the influence of the presence of liquid droplets on the airflow by comparing single-phase flow field to the air-phase motion in two-phase flow configuration. Furthermore, by analysing the continuous-phase and the discrete-phase properties, some aspects of the interaction between the two phases are shown.