Experimental studies on dragon wash phenomena*

The experiment is carried out to study the low frequency surface waves due to the horizontal high frequency excitation. The viscous effect of water was neglected as a first approximation in the earlier papers on this subject. In contrast, we find the viscosity is important to achieve the low frequency water wave with the cooperation of hundreds of “finger” waves. Shadowgraphs have been taken qualitatively using laser sheet and vertical velocities of surface waves have been measured quantitatively by Polytec Scanning Vibrometer. The viscous cooperation effects are shown to be the most important mechanism for the dragon wash phenomena.