LAUSR

Abstract The Kaye effect is a phenomenon whereby a jet of fluid poured onto a surface appears to leap on impact, rather than stagnate or coil as expected. Since it was first described in 1963, several authors have attempted to explain the mechanism by which the phenomenon occurs, although to date no complete explanation for the behaviour exists. Current evidence points towards the existence of an air layer between the jet and the heap which enables slip. We show that the Kaye effect does not occur in a vacuum, indicating that the air layer is crucial for the effect to occur. By use of control volume analysis we show that viscoelasticity plays a key role in the Kaye effect, and this role is two-fold. Firstly, viscoelasticity appears to increase air entrainment, and secondly, it reduces the pressure required to bend the jet, allowing a thicker air layer to be sustained. Shear thinning behaviour reduces this viscoelastic response. These findings provide new insight into a problem that has puzzled rheologists for over half a century.