Further, in comparison to swimming alone, pitching motions increase the energetic efficiency of the group while heaving motions result in a slight increase in the swimming speed. We find that, independent of the flapping mode, the follower passively stabilizes at discrete locations in the wake of the leader, consistent with the heaving foil experiments, but pitching swimmers exhibit tighter and more cohesive formations. Here, we propose a minimal approach based on the vortex sheet model that captures salient features of the flow interactions among flapping swimmers, and we study the free swimming of a pair of in-line swimmers driven with identical heaving or pitching motions. Recent experiments suggest that flow interactions stabilize in-tandem formations of heaving foils. Although flow interactions are thought to be beneficial for schooling, their exact effects on the speed, energetics, and stability of the group remain elusive. The proposed model shows improved accuracy at the cost of a mildly increased computational effort, thereby constituting an ideal basis for research on fish hydrodynamics.įish schools are ubiquitous in marine life. Using a pair of vortex sheets that span approximately 80% of the fish body length with a separation distance of approximately 50% of the body width, the model is successful in predicting the fluid flow around the swimming fish for a range of background flow speeds and channel widths. To address this issue, we propose an alternative model that replaces each vortex in the pair with a sheet along the fish length. We demonstrate that dipole-based models are accurate in capturing key features of the fluid flow, but cannot predict the elongated flow streamlines around the fish that are evident in CFD. The locomotory patterns of a fish undergoing carangiform swimming are reconstructed from existing experimental data, which are used as inputs to CFD simulations of a fish swimming in a channel flow. Here, we embark on a computational fluid dynamics (CFD) campaign informed by experimental data to validate the accuracy of dipole-based models. Dipole-based models that assimilate fish to pairs of vortices are particularly enticing, but yet to be thoroughly validated. Due to their mathematical tractability, models based on potential flow are preferred in the study of bidirectional interactions of fish with their surroundings. We find that the two dipoles exhibit regular behavior consisting of either colliding, synchronizing or diverging trajectories depending on their relative spacing and relative orientation.Įlucidating the hydrodynamics of fish swimming is critical to identifying the processes underlying fish orientation and schooling. For each system, we examine in detail the dynamic interactions of two dipoles, comparing and contrasting their behavior as function of initial conditions. The other system turns out to lead to the so-called Jeffery's orbits which are obtained in models of elongated bodies in viscous shear flows. One system is consistent with the finite-dipole model of Tchieu, Kanso & Newton (2013) based on constrained vortex pairs. We discuss two dipole systems that differ only by the detail of how an individual dipole aligns itself with the local flow gradient. The resulting equations of motion for the dipoles positions and orientations reflect that (i) each dipole has a self-induced velocity and is advected by the local fluid velocity induced by other dipoles and (ii) each dipole tries to align itself in response to the local flow gradient. A dynamical system governing the interaction of N point dipoles is derived.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |