Compact zero-mass pulsatile jet actuators are proposed for low-speed maneuvering and station keeping of small underwater vehicles. The flow field of such jets are initially dominated by vortex ring formation. Pinched-off vortices characterize the extremum impulse accumulated by the leading vortex ring in a vortex ring formation process. Relevant parameters in this process are identified in orde...

The time-averaged thrust of an incompressible fully pulsed jet containing a period of no flow between pulses is studied experimentally as a function of pulsing duty cycle SrL and the ratio of the ejected slug length (per pulse) to the jet diameter L/D. The parameter ranges investigated were 2 <– L/D <– 6 and 0.1 <– SrL <– 0.98. Significant thrust augmentation by pulsing was observed over the en...

The purpose of this study is to analyse the transport and stirring of fluid that occurs owing to the formation and growth of a laminar vortex ring. Experimental data was collected upstream and downstream of the exit plane of a piston–cylinder apparatus by particle-image velocimetry. This data was used to compute Lagrangian coherent structures to demonstrate how fluid is advected during the tran...

Animal phyla that require macro-scale fluid transport for functioning have repeatedly and often independently converged on the use of jet flows. During flow initiation these jets form fluid vortex rings, which facilitate mass transfer by stationary pumps (e.g. cardiac chambers) and momentum transfer by mobile systems (e.g. jet-propelled swimmers). Previous research has shown that vortex rings g...

A planar model of a lifting surface descending into its own wake is constructed with the aim of demonstrating some underlying mechanisms of the ‘vortex ring’ state that may be entered by a rotary wing aircraft during a vertical descent. The model uses line vortices that are periodically released from a point in space and then allowed to evolve in a constrained manner. For low descent velocities...

Birds and bats are known to employ two different gaits in flapping flight, a vortex-ring gait in slow flight and a continuous-vortex gait in fast flight. We studied the use of these gaits over a wide range of speeds (1-17 ms(-1)) and transitions between gaits in cockatiels (Nymphicus hollandicus) and ringed turtle-doves (Streptopelia risoria) trained to fly in a recently built, variable-speed w...

A simple and ultra-compact integrated optical vortex beam receiver device is presented. The device is based on the coupling between the optical vortex modes and whispering gallery modes in a micro-ring resonator via embedded angular gratings, which provides the selective reception of optical vortex modes with definitive total angular momentum (summation of spin and orbital angular momentum) thr...

We investigated the detailed kinematics and wake structure of lesser dog-faced fruit bats (Cynopterus brachyotis) flying in a wind tunnel. High speed recordings of the kinematics were conducted to obtain three-dimensional reconstructions of wing movements. Simultaneously, the flow structure in the spanwise plane perpendicular to the flow stream was visualized using time-resolved particle image ...

We calculate the energetic structure of defect cores and propose controlled methods to imprint a nontrivially entangled vortex pair that undergoes non-Abelian vortex reconnection in a biaxial nematic spin-2 condensate. For a singular vortex, we find three superfluid cores in addition to depletion of the condensate density. These exhibit order parameter symmetries that are different from the dis...

We give a brief overview of the recent advances in nonlinear singular optics that studies the propagation and stability of optical vortices in nonlinear media, with the emphasis on the properties of vortex solitons and rotating azimuthons. In general, self-focusing nonlinearity generates the azimuthal instability of vortex beams, but it can support novel types of stable (or metastable) self-tra...