Tuna locomotion: a computational hydrodynamic analysis of finlet function

Abstract

Finlets are a series of small non-retractable fins common to scombrid fishes (mackerels, bonitos and tunas), which are known for their high swimming speed. It is hypothesized that these small fins could potentially affect propulsive performance. Here, we combine experimental and computational approaches to investigate the hydrodynamics of finlets in yellowfin tuna ( Thunnus albacares ) during steady swimming. High-speed videos were obtained to provide kinematic data on the in vivo motion of finlets. High-fidelity simulations were then carried out to examine the hydrodynamic performance and vortex dynamics of a biologically realistic multiple-finlet model with reconstructed kinematics. It was found that finlets undergo both heaving and pitching motion and are delayed in phase from anterior to posterior along the body. Simulation results show that finlets were drag producing and did not produce thrust. The interactions among finlets helped reduce total finlet drag by 21.5%. Pitching motions of finlets helped reduce the power consumed by finlets during swimming by 20.8% compared with non-pitching finlets. Moreover, the pitching finlets created constructive forces to facilitate posterior body flapping. Wake dynamics analysis revealed a unique vortex tube matrix structure and cross-flow streams redirected by the pitching finlets, which supports their hydrodynamic function in scombrid fishes. Limitations on modelling and the generality of results are also discussed.

Bio-Inspired Propulsion: Towards Understanding the Role of Pectoral Fin Kinematics in Manta-like Swimming

“…A joint-based skeletal structure bound to a polygonal-mesh skin for modeling the manta motion is used in this study. This technique has been successfully applied to reconstructions of bird flight and tuna body with caudal fin and finlet motion [ 27 , 28 ]. The manta ray model includes complex geometric and kinematic features of its biological counterpart, producing a 3-D model with manta-like swimming motion.…”

Tail shapes lead to different propulsive mechanisms in the body/caudal fin undulation of fish

“…In addition, this numerical method has also been successfully used by other researchers to investigate the hydrodynamics of fish swimming. 14,30 The governing equations of the flow are: where boldu denotes the velocity vector and ρ and ν are the density and kinematic viscosity of water, respectively. The non-uniform Cartesian grid covers the entire computational domain, including both the fluid region and the solid body.…”

Extracting signature responses from respiratory flows: Low‐dimensional analyses on Direct Numerical Simulation‐predicted wakes of a flapping uvula

“…Six models will be considered from the combination of K1-2 and m1-3 (K1m1, K1m2, K1m3, K2m1, K2m2, and K2m3) insects, 48,49 birds, 50,51 and fishes. 52,53 More details of this solver can be viewed in our previous works. 53,54 Briefly, the airway surface was meshed with unstructured elements and immersed within structured Cartesian grids.…”

“…An in‐house DNS solver 47 based on Cartesian‐grid finite‐difference immersed‐boundary method was implemented in this study (Figure 2A). This solver has been well tested in the flapping propulsion simulations for insects, 48,49 birds, 50,51 and fishes 52,53 . More details of this solver can be viewed in our previous works 53,54 .…”