Surface wave generation via a gas-jet penetration into a liquid sheet

The mechanism and frequency of surface wave generated by normal wall-jet impingement at a vertical gas-liquid interface were experimentally characterized for a gas-jet penetrating into a liquid sheet. The oscillatory gas-liquid interface accompanied by surface wave generation and propagation were captured with a high-speed camera. Periodic oscillations of the vertical gas-liquid interface were revealed in the context of energy transfer from the wall-jet to surface waves. In addition, wave generation was considered as a means of releasing the maximum interfacial elastic energy. The radial distance between the waist and neck of the wavy interface was defined as the amplitude and the characteristic amplitude was adopted to reveal periodic deformation of the wavy interface during dynamic oscillations. Furthermore, the characteristic wavelength, i.e. vertical distance between waist and neck, was about one third of the liquid sheet thickness, irrespective of penetration parameters, such as gas flow rate, jet height, and liquid sheet thickness. The effects of those parameters on the surface wave generation frequency were analyzed. A combined dimensionless parameter of Froude number and the ratio of jet height to nozzle diameter was used to normalize the surface wave generation frequency with all the penetration parameters. It was found that the frequency could be expressed by a natural exponential function with the combined dimensionless parameter for normalization via fitting analysis. This work should be helpful to characterize interfacial motion in actual industrial applications.