Actuation of Liquid Flow by Guided Acoustic Waves on Punched Steel Tapes with Protruding Loops

In a biomimetic approach the feasibility of liquid flow actuation by vibrating protruding structures excited via guided acoustic waves is investigated. Inspired by periodically beating cilia the loop part of a punched metallic hook-and-loop tape with tilted protruding loops was used as a waveguide for plate waves in water. Such waves were excited in the frequency range of 110 Hz to 220 Hz by directly coupling the tape to a loudspeaker membrane. A flow generated in the tilt direction of the loops with velocities up to 60 mm·s −1 was visualized by ink droplets deposited on the tape. The phenomenon persisted, when the protruding length of the loops was reduced by decreasing the protrusion angle. However, after closing the punch holes near the loops with sticking tape streaming could not be observed any longer. The same happened with open punch holes when the ink was replaced by glycerol. Low-frequency acoustic streaming around vibrating sharp edges is proposed as an explanation for the observed phenomena. Applications are expected with respect to the modification of flow profiles and the enhancement of transport processes along and across liquid-solid boundaries.