The numerical comparison of flow patterns and propulsive performances for the hydromedusaeSarsia tubulosaandAequorea victoria

Abstract

SUMMARYThe thrust-generating mechanism of a prolate hydromedusa Sarsia tubulosa and an oblate hydromedusa Aequorea victoria was investigated by solving the incompressible Navier-Stokes equations in the swirl-free cylindrical coordinates. The calculations clearly show the vortex dynamics related to the thrust-generating mechanism, which is very important for understanding the underlying propulsion mechanism. The calculations for the prolate jetting hydromedusa S. tubulosa indicate the formation of a single starting vortex ring for each pulse cycle with a relatively high vortex formation number. However, the calculations for the oblate jet-paddling hydromedusa A. victoria indicate shedding of the opposite-signed vortex rings very close to each other and the formation of large induced velocities along the line of interaction as the vortices move away from the hydromedusa in the wake. In addition to this jet propulsion mechanism, the hydromedusa's bell margin acts like a paddle and the highly flexible bell margin deforms in such a way that the low pressure leeward side of the bell margin has a projected area in the direction of motion. This thrust is particularly important during refilling of the subumbrella cavity where the stopping vortex causes significant pressure drag. The swimming performances based on our numerical simulations, such as swimming velocity, thrust, power requirement and efficiency, were computed and support the idea that jet propulsion is very effective for rapid body movement but is energetically costly and less efficient compared with the jet-paddling propulsion mechanism.

Flow structure and transport characteristics of feeding and exchange currents generated by upside-down Cassiopea jellyfish

“…Recent work using digital particle image velocimetry (DPIV) and computational fluid dynamics has elucidated the mechanisms by which jellyfish effectively propel themselves and feed. The specific details on the relationship between unsteady fluid dynamics and swimming efficiency have been investigated using mathematical modeling (Daniel, 1983;Daniel, 1984;Dabiri et al, 2007), experiments (Costello and Colin, 1994;McHenry and Jed, 2003;Dabiri et al, 2005) and numerical simulations (Sahin et al, 2009;Lipinski and Mohseni, 2009). More recent studies have used DPIV and Lagrangian coherent structures (LCS) to characterize the vortex shedding and fluid mixing due to the pulsations of the bell (Dabiri et al, 2010;Peng and Dabiri, 2008a;Peng and Dabiri, 2008b;Peng and Dabiri, 2009;Lipinski and Mohseni, 2009).…”

A numerical study of the effects of bell pulsation dynamics and oral arms on the exchange currents generated by the upside-down jellyfish Cassiopea xamachana

“…Jellyfish have been the subject of vigorous biomechanical and fluid dynamic research aimed at understanding the nature of unsteady propulsion (Dabiri, 2005;Dabiri et al, 2007;Daniel, 1985;Daniel, 1995;Demont and Gosline, 1988;Lipinski and Mohseni, 2009;Rudolf, 2007;Sahin et al, 2009). Demont and Gosline (Demont and Gosline, 1988) and Daniel (Daniel, 1985) showed that the bell is driven at its resonant frequency, which increases the efficiency of this form of unsteady locomotion.…”

“…Demont and Gosline (Demont and Gosline, 1988) and Daniel (Daniel, 1985) showed that the bell is driven at its resonant frequency, which increases the efficiency of this form of unsteady locomotion. More recent studies have used digital particle image velocimetry (dPIV) and Lagrangian coherent structures to characterize the vortex shedding, mixing and particle capture associated with jellyfish locomotion (Dabiri, 2008;Dabiri et al, 2010;Peng and Dabiri, 2008a;Peng and Dabiri, 2008b;Peng and Dabiri, 2009;Sahin et al, 2009). Rudolf used immersed boundary methods to develop animations of swimming jellyfish (Rudolf, 2007).…”

Ontogenetic propulsive transitions by medusaeSarsia tubulosa

“…For both swimming modes, contraction of the bell by subumbrellar muscles expels fluid from the subumbrellar cavity and creates a starting vortex (Dabiri et al, 2005). During relaxation of the same subumbrellar muscles, fluid is brought into the subumbrellar cavity as a result of a drop in internal pressure, and creates a stopping vortex (Dabiri et al, 2005;Sahin et al, 2009). Rowing propulsion is characterized by strong interactions between these stopping and starting vortices to achieve a propulsive advantage (Dabiri et al, 2005).…”