Note: 2D Farady Flows

Abstract: Faraday waves are capillary ripples that form onthe surface of a fluid being subject to vertical shaking. Al-though it is well known that the form and shape of the wavespattern depend on driving amplitude and frequency, only recent studies discovered the existence of a horizontal veloc-ity field at the surface, called Faraday flow, which exhibitsattributes of two-dimensional turbulence. However, despitethe increasing attention towards the inverse energy flux inthe Faraday flow and other not strictly two-dimensional sys-tems, very little is known about the velocity fields develop-ing beneath the fluid surface. In this study planar velocityfields are measured by means of particle image velocime-try (PIV) with high spatial and temporal resolution on thewater surface and below it. A sudden drop in velocity isobserved immediately below the water surface, such that at5 mm below the water surface the mean absolute velocitiesare already about 6.5 times smaller than the surface veloc-ity. Additionally, the flow structures below the surface arefound to comprise much larger spatial scales than those onthe surface. These large structures are also found to be slowand temporarily persistent, as proven by analysing the auto-correlation of the velocity fields in time.