Vortex Formation with a Snapping Shrimp Claw

Abstract

Snapping shrimp use one oversized claw to generate a cavitating high speed water jet for hunting, defence and communication. This work is an experimental investigation about the jet generation. Snapping shrimp (Alpheus-bellulus) were investigated by using an enlarged transparent model reproducing the closure of the snapper claw. Flow inside the model was studied using both High-Speed Particle Image Velocimetry (HS-PIV) and flow visualization. During claw closure a channel-like cavity was formed between the plunger and the socket featuring a nozzle-type contour at the orifice. Closing the mechanism led to the formation of a leading vortex ring with a dimensionless formation number of approximate ΔT*≈4. This indicates that the claw might work at maximum efficiency, i.e. maximum vortex strength was achieved by a minimum of fluid volume ejected. The subsequent vortex cavitation with the formation of an axial reentrant jet is a reasonable explanation for the large penetration depth of the water jet. That snapping shrimp can reach with their claw-induced flow. Within such a cavitation process, an axial reentrant jet is generated in the hollow cylindrical core of the cavitated vortex that pushes the front further downstream and whose length can exceed the initial jet penetration depth by several times.

Transient Cavitation by Quick Closing Pincers

“…Photos 9 to 14 show the progressive growth of two counter-rotating travelling vortices in the free fluid; an upper vortex ring (indicated as V1) of small bubbles and a lower cavitating vortex ring (indicated as V2). A similar flow of two counter-rotating vortices (with no cavitation) at the exit of the diverging nozzle is experimentally observed in [4]. The inception and growth of a cavitating sheet in the upper wall of the throat is also observed from snapshot 13 onwards.…”

“…It is remarked that a very similar value of the Ca parameter was calculated for the shrimp claw and the pincers device; this value is less than 1, thus indicating the occurrence of cavitation [8] in both systems, a fact corroborated by our experiments. Table 1 Comparison between parameters of the shrimp claw and the pincers device, the data in the first column were taken from [4].…”

“…Nevertheless, greater control, repeatability and scalability may be attained through the use of artificial devices to emulate the claw geometry and its fast closing mechanism, in order to understand and clarify the phenomena associated with the emission of the snap sound. In this sense, Hess et al [4] fabricated and tested an enlarged transparent model (which basically consists of a pivoting plunger and a socket) to reproduce the closure of the snapper claw and the flow generated by this process. Experiments were performed using both high-speed particle image velocimetry (HS-PIV) and flow visualization.…”

High-speed visualization of vortical cavitation using synchrotron radiation

“…In reference to high-velocity, turbulent liquid flows, onset of a recirculating-flow pattern having a significant vorticity magnitude is possible to cause enough tension at its core, so as to force the liquid to nucleate, hence, giving rise to a vortical cavity. Vortical cavitation is a flow phenomenon encountered in the natural world (for instance see (Hess 2011)), as well as in a wide range of engineering applications comprising, among others, ship propellers, turbomachinery blades, high-pressure pumps, fuel injectors and mechanical heart valves (Kini et al 2000). Emergence of cavitation in engineering applications is accompanied by either attractive, i.e.…”

Hunting in archerfish – an ecological perspective on a remarkable combination of skills

“…In terms of underwater jets, which are widespread among aquatic animals (e.g. Brown, 2012;Mann and Patterson, 2013;Marshall et al, 2014), archerfish do not excel in any way, and the record in terms of power is held by snapping shrimp, whose claws can produce velocity fields with an associated 10 5 Pa pressure drop that can cause serious damage (Versluis et al, 2000;Hess et al, 2013).…”