Controlling large-scale waves in downward annular flow far from the inlet

Disturbance waves are the key element of annular gas-liquid flows. They produce liquid entrainment and affect heat and mass transfer in the flow. Ability to control (initiate or regularize) them can be useful for optimization of industrial equipment or carrying out in-depth experimental studies. Here we continue our earlier works wherein the possibilities of controlling the disturbance waves by means of inlet forcing were investigated. In the present study, we employ different conditions, including larger pipe diameter, longer distance from the inlet and different range of gas speeds. The results confirm all the conclusions made earlier, widening their range of applicability and improving our understanding of the important factors affecting capabilities and limitations of flow control. In particular, it was found that the flow control works at relatively large distances (90 pipe diameters) from the inlet without showing any signs of decay. Even in absence of gas flow, it is possible to create large-scale waves on thick films which remain regular over the long distance. Spatiotemporal dynamics of small-scale waves produced by the large waves in these conditions has unexpected similarity to that of disturbance waves.