In the present work, a LIF technique is applied for investigation of gas-sheared film flow in horizontal rectangular duct. The technique makes it possible to perform field measurements of local film thickness, resolved in both space and time, similar to the work of Alekseenko et al. (2009). The flat shape and large transverse size of the duct allow us to resolve the film thickness in transverse coordinate as well. Alekseenko et al. (2012) attempted to do this in annular downward flow, but, for technical reasons, the sampling frequency was not high enough in their experiments. More recently Alekseenko et al. (2014a) showed that the LIF technique can also detect entrained droplets. The technique allows the simultaneous study of three-dimensional wavy structures and liquid entrainment, and can improve understanding of the entrainment phenomenon.
