Starting jet formation through eversion of elastic sheets

Abstract

Motivated by biological systems, such as human hearts and the propulsors of aquatic creatures, the interaction between deformable structures and fluid jets has drawn considerable attention to understand the mechanism of effective fluid transport through such jets. In this study, the formation of a starting jet through a novel eversion process is investigated experimentally using a simple vortex generator model with everted sheets. The ends of two everted sheets are clamped at either side of a rectangular flow channel, with the other free ends in contact with each other in the middle of the channel. Geometric and kinematic parameters, such as the length and bending rigidity of the everting sheets and the speed of the piston, are varied to examine their effects on the deformation of the sheets and the formation of the jet. By introducing a dimensionless bending rigidity, the behaviour of the sheets during the eversion process can be correlated with jet characteristics such as the velocity profile and hydrodynamic impulse. The interaction between the starting jet and the everting sheets enables a notably faster jet with an improved hydrodynamic impulse to be developed within a shorter stroke time.