Numerical investigation of the hydrodynamics of carangiform swimming in the transitional and inertial flow regimes

Abstract

SUMMARYFor all Re, however, the swimming power is shown to be significantly greater than that required to tow the rigid body at the same speed. We also show that the variation of the total drag and its viscous and form components with St depend on the Re. For Re=300, body undulations increase the drag over the rigid body level, while significant drag reduction is observed for Re=4000. This difference is shown to be due to the fact that at sufficiently high Re the drag force variation with St is dominated by its form component variation, which is reduced by undulatory swimming for St>0.2. Finally, our simulations clarify the 3D structure of various wake patterns observed in experiments -single and double row vortices -and suggest that the wake structure depends primarily on the St. Our numerical findings help elucidate the results of previous experiments with live fish, underscore the importance of scale (Re) effects on the hydrodynamic performance of carangiform swimming, and help explain why in nature this mode of swimming is typically preferred by fast swimmers.

Effects of body elasticity on stability of underwater locomotion

“…On the one hand, the deformation modes may add to the bluffness of the swimmer's shape. On the other hand, separation and shedding may be hindered by a traveling-wave deformation if the wave speed is faster than the swimming speed; see, for example, Borazjani & Sotiropoulos (2008), (2009a,b); [23,24]. In reality, drag forces will slow down the passively swimming fish and passive locomotion cannot be maintained.…”

Soft tissue preservation in a fossil marine lizard with a bilobed tail fin

“…Given that the tail fluke represents the distalmost portion of the vertebral axis, and thus is the place where water accelerated posteriorly leaves the body, its shape dramatically influences performance in axial-undulatory swimming animals [37][38][39] . For instance, the tail fin of ERMNH HFV 197 shows a number of features for improved efficiency by reduced induced drag, including the backward-curved leading edge and virtually straight trailing edge of the dorsal fin lobe.…”

Optimal shape and motion of undulatory swimming organisms

“…It is important to point out, however, that our primary interest is in the correct scaling of quantities with Re and the proper dependence on kinematic and geometric parameters, rather than in the quantitative accuracy (requiring substantially greater computational cost). For example, we have compared the scaling of the stride length with Re calculated by Lighthill's model and empirical drag formula with that from a more sophisticated hydrodynamic model [7]. Over the wide range of Re, the slopes of the predicted scaling agree to within approximately 10 per cent.…”

“…Modelling hydrodynamics with higher accuracy might be achieved at low Reynolds numbers Re (O (10 3 -10 4 )) where CFD models solving the viscous flow equations [3,7] are computationally feasible. However, the above Re-range covers only a small range of Re considered in this paper (which basically covers the entire range of fish and cetacean swimming).…”