34 research outputs found
Transition in swimming direction in a model self-propelled inertial swimmer
We propose a reciprocal, self-propelled model swimmer at intermediate Reynolds numbers (Re). Our swimmer consists of two unequal spheres that oscillate in antiphase, generating nonlinear steady streaming (SS) flows. We show computationally that the SS flows enable the swimmer to propel itself, and also switch direction as Re increases. We quantify the transition in the swimming direction by collapsing our data on a critical Re and show that the transition in swimming directions corresponds to the reversal of the SS flows. Based on our findings, we propose that SS can be an important physical mechanism for motility at intermediate Re
In-phase schooling hinders linear acceleration in wavy hydrofoils paired in parallel across various wavelengths
This study examines the impact of in-phase schooling on the hydrodynamic
efficiency during linear acceleration in a simplified model using two
undulating NACA0012 hydrofoils arranged in phalanx formation as a minimal
representation of a fish school. The research focuses on key parameters, namely
Strouhal (0.2-0.7) and Reynolds (1000-2000) numbers, and explores the effect of
varying fish-body wavelengths (0.5-2), reflecting natural changes during actual
fish linear acceleration. Contrary to expectations, in-phase schooling did not
enhance acceleration performance. Both propulsive efficiency and net thrust
were found to be lower compared to solitary swimming and anti-phase schooling
conditions. The study also identifies and categorizes five distinct flow
structure patterns within the parameters investigated, providing insight into
the fluid dynamics of schooling fish during acceleration.Comment: 19 pages, more authors to be confirmed and added in the futur
Hydrodynamics of Biomimetic Marine Propulsion and Trends in Computational Simulations
[Abstract] The aim of the present paper is to provide the state of the works in the field of hydrodynamics and computational simulations to analyze biomimetic marine propulsors. Over the last years, many researchers postulated that some fish movements are more efficient and maneuverable than traditional rotary propellers, and the most relevant marine propulsors which mimic fishes are shown in the present work. Taking into account the complexity and cost of some experimental setups, numerical models offer an efficient, cheap, and fast alternative tool to analyze biomimetic marine propulsors. Besides, numerical models provide information that cannot be obtained using experimental techniques. Since the literature about trends in computational simulations is still scarce, this paper also recalls the hydrodynamics of the swimming modes occurring in fish and summarizes the more relevant lines of investigation of computational models
How wavelength affects the hydrodynamic performance of two accelerating mirror-symmetric slender swimmers
Fish schools are capable of simultaneous linear acceleration. To reveal the
underlying hydrodynamic mechanism, we numerically investigate how Reynolds
number , Strouhal number and wavelength
affect the mean net thrust and net propulsive efficiency
of two side-by-side hydrofoils undulating in anti-phase. In total,
cases are simulated using immersed boundary method. The thrust increases
significantly with wavelength and Strouhal number, yet only slightly with the
Reynolds number. We apply a symbolic regression algorithm to formulate this
relationship. Furthermore, we find that mirror-symmetric schooling can achieve
a \textit{net} thrust more than ten times that of a single swimmer, especially
at low Reynolds numbers. The highest efficiency is obtained at and
, where is consistent with that observed in the
linear-accelerating natural swimmers, \eg Crevalle jack. Six distinct flow
structures are identified. The highest thrust corresponds to an asymmetric flow
pattern, whereas the highest efficiency occurs when the flow is symmetric with
converging vortex streets.Comment: This paper has been accepted by Physics of Fluids. This is the
accepted versio
Tailbeat perturbations improve swimming efficiency in self-propelled flapping foils
Recent studies have shown that superimposing rhythmic perturbations to oscillating tailbeats could simultaneously enhance both the thrust and efficiency (Lehn et al., Phys. Rev. Fluids, vol. 2, 2017, p. 023101; Chao et al., PNAS Nexus, vol. 3, 2024, p. 073). However, these investigations were conducted with a tethered flapping foil, overlooking the self-propulsion intrinsic to real swimming fish. Here, we investigate how the high-frequency, low-amplitude superimposed rhythmic perturbations impact the self-propelled pitching and heaving swimming of a rigid foil. The swimming-speed-based Reynolds number ranges from 1400 to 2700 in our study, depending on superimposed perturbations and swimming modes. Numerical results reveal that perturbations significantly increase swimming speeds in both pitching and heaving motions, while enhancing efficiency exclusively in the heaving motion. Further derived scaling laws elucidate the relationships of perturbations with speeds, power costs and efficiency, respectively. These findings not only hypothesise the potential advantages of perturbations in biological systems, but also inspire designs and controls in biomimetic propulsion and manoeuvring within aquatic environments