Swimmers’ wake structures are not reliable indicators of swimming performance

Floryan, Daniel; Buren, Tyler Van; Smits, Alexander J.

doi:10.1088/1748-3190/ab6fb9

Cited by 33 publications

(20 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similarly, Taylor (2018) writes that an explanation of propulsive efficiency given only in terms of the wake feels a little incomplete, and notes that Eloy (2012) suggested that efficient development of the wake may be a consequence, rather than a cause, of efficient propulsion. See also Floryan, Van Buren & Smits (2019).…”

Section: Wake Structurementioning

confidence: 99%

Undulatory and oscillatory swimming

Smits¹

2019

J. Fluid Mech.

201

113

View full text Add to dashboard Cite

Theory and modelling remain central to improving our understanding of undulatory and oscillatory swimming. Simple models based on added mass can help to give great insight into the mechanics of undulatory swimming, as demonstrated by animals such as eels, stingrays and knifefish. To understand the swimming of oscillatory swimmers such as tuna and dolphins, models need to consider both added mass forces and circulatory forces. For all types of swimming, experiments and theory agree that the most important velocity scale is the characteristic lateral velocity of the tail motion rather than the swimming speed, which erases to a large extent the difference between results obtained in a tethered mode, compared to those obtained using a free swimming condition. There is no one-to-one connection between the integrated swimming performance and the details of the wake structure, in that similar levels of efficiency can occur with very different wake structures. Flexibility and viscous effects play crucial roles in determining the efficiency, and for isolated propulsors changing the profile shape can significantly improve both thrust and efficiency. Also, combined heave and pitch motions with an appropriate phase difference are essential to achieve high performance. Reducing the aspect ratio will always reduce thrust and efficiency, but its effects are now reasonably well understood. Planform shape can have an important mitigating influence, as do non-sinusoidal gaits and intermittent actuation.

show abstract

Section: Wake Structurementioning

confidence: 99%

Undulatory and oscillatory swimming

Smits¹

2019

J. Fluid Mech.

201

113

View full text Add to dashboard Cite

show abstract

“…Godoy-Diana, Aider & Wesfreid 2008). Floryan, Van Buren & Smits (2020) have reinterpreted results in the literature and pointed out that the wake-structure-based performance assessment of swimmers may be misleading. For example, Godoy-Diana et al.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic performance of slender swimmer: effect of travelling wavelength

2022

View full text Add to dashboard Cite

The impact of Strouhal number St (= 0.1–1.0), Reynolds number Re (= 50–2000) and dimensionless wavelength λ (= 0.5–2.0) on the hydrodynamic performance of a travelling wavy foil of a constant length is extensively investigated. The relationship of time-mean thrust with St, Re and λ is presented, suggesting that the propulsive force increases with increasing St, Re and λ. As such, the drag–thrust boundary advances as these parameters increase. A shorter λ makes the thrust steadier while a longer λ enhances the maximum instantaneous thrust. The latter is beneficial for prey to escape from a predator. The fluid added mass caused by the foil oscillation increases with St and λ but declines with Re (<500). Seven types of wake structures produced by the foil are identified, discussed and connected to thrust generation, showing how St, Re and λ affect the fluid dynamics, wake transition, vortex strength, wake jet, velocity, added mass, added damping, power input, efficiency and pressure profiles. The outcome of this work renders a physical basis for understanding the swimming of aquatic animals.

show abstract

“…In other words, by evaluating the momentum associated to the vortex clusters right after the fast start, they manage to estimate the swimming velocity at the end of the maneuver. However, as suggested by many authors 21 – 24 and clearly stated by Zhang 25 , the shed vortices behave like terrestrial footprints hence they are not telling the whole story about the fish dynamics. The debate on this point is quite subtle and we like to add a further deepening by reporting the main findings obtained by our numerical simulations.…”

Section: Discussionmentioning

confidence: 93%

The fish ability to accelerate and suddenly turn in fast maneuvers

Paniccia

Graziani

Lugni

et al. 2022

Sci Rep

View full text Add to dashboard Cite

Velocity burst and quick turning are performed by fish during fast maneuvers which might be essential to their survival along pray–predator encounters. The parameters to evaluate these truly unsteady motions are totally different from the ones for cruising gaits since a very large acceleration, up to several times the gravity, and an extreme turning capability, in less than one body length, are now the primary requests. Such impressive performances, still poorly understood, are not common to other living beings and are clearly related to the interaction with the aquatic environment. Hence, we focus our attention on the water set in motion by the body, giving rise to the relevant added mass and the associated phenomena in transient conditions, which may unveil the secret of the great maneuverability observed in nature. Many previous studies were almost exclusively concentrated on the vortical wake, whose account, certainly dominant at steady state, is not sufficient to explain the entangled transient phenomena. A simple two-dimensional impulse model with concentrated vorticity is used for the self-propulsion of a deformable body in an unbounded fluid domain, to single out the potential and the vortical impulses and to highlight their interplay induced by recoil motions.

show abstract

Swimmers’ wake structures are not reliable indicators of swimming performance

Abstract: The structure of swimmers' wakes is often assumed to be an indicator of swimming performance. Here, we discuss three cases where this assumption fails. In general, great care should be taken in deriving any conclusions about swimming performance from the wake flow pattern.

Cited by 33 publications

References 41 publications

Undulatory and oscillatory swimming

Undulatory and oscillatory swimming

Hydrodynamic performance of slender swimmer: effect of travelling wavelength

The fish ability to accelerate and suddenly turn in fast maneuvers

Contact Info

Product

Resources

About