Hydrodynamics of swimming in stingrays: numerical simulations and the role of the leading-edge vortex

Abstract

Stingrays, in contrast with many other aquatic animals, have flattened disk-shaped bodies with expanded pectoral 'wings', which are used for locomotion in water. To discover the key features of stingray locomotion, large-eddy simulations of a self-propelled stingray, modelled closely after the freshwater stingray, Potamotrygon orbignyi, are performed. The stingray's body motion was prescribed based on three-dimensional experimental measurement of wing and body kinematics in live stingrays at two different swimming speeds of 1.5 and 2.5L s −1 (L is the disk length of the stingray). The swimming speeds predicted by the self-propelled simulations were within 12 % of the nominal swimming speeds in the experiments. It was found that the fast-swimming stingray (Reynolds number Re = 23 000 and Strouhal number St = 0.27) is approximately 12 % more efficient than the slow-swimming one (Re = 13 500, St = 0.34). This is related to the wake of the fast-and slow-swimming stingrays, which was visualized along with the pressure on the stingray's body. A horseshoe vortex was discovered to be present at the anterior margin of the stingray, creating a low-pressure region that enhances thrust for both fast and slow swimming speeds. Furthermore, it was found that a leading-edge vortex (LEV) on the pectoral disk of swimming stingrays generates a low-pressure region in the fast-swimming stingray, whereas the low-and high-pressure regions in the slow-swimming one are in the back half of the wing and not close to any vortical structures. The undulatory motion creates thrust by accelerating the adjacent fluid (the added-mass mechanism), which is maximized in the back of the wing because of higher undulations and velocities in the back. However, the thrust enhancement by the LEV occurs in the front portion of the wing. By computing the forces on the front half and the back half of the wing, it was found that the contribution of the back half of the wing to thrust in a slow-swimming stingray is several-fold higher than in the fast-swimming one. This indicates that the LEV enhances thrust in fast-swimming stingrays and improves the efficiency of swimming.

Scaling trends of bird’s alular feathers in connection to leading-edge vortex flow over hand-wing

“…Collectively, the findings of this study advance our understanding of the unique ways nature utilizes LEVs to augment flight. To date, LEVs have been implicated in the flight of insects [33][34][35][36][37] , slow-flying bats 38 , hummingbirds 39 , swifts 15,16 , large birds such as geese 40 , slow-flying Passerines 17 , stingrays 41 , fish tails 42 , and auto-rotating seeds 43 . Our results confirm the hypothesis of refs.…”

Effects of Reynolds and Womersley Numbers on the Hemodynamics of Intracranial Aneurysms

“…The details of the overset-CURVIB method can be found in [20]. The method has been validated against experimental and benchmark solutions [20, 24] and has been applied to a variety of problems such as cardiovascular flows [17, 25–28], aquatic swimming [23, 29], and rheology [30]. Furthermore, we have validated our method for flows inside an immersed body by comparing our results with the measurements of the pulsatile flow through a 90° bend in Appendix.…”

Hydrodynamic Performance of Aquatic Flapping: Efficiency of Underwater Flight in the Manta

“…By calculating the Froude efficiency (Figure 12b), the efficiency of the manta ray can be placed in context with other swimming animals used in the studies of Borazjani and Sotiropoulos [48,49] and Bottom et al [50]. In these works, the Froude efficiency was 19% for inviscid anguilliform swimmers, that is eel-like swimmers [49], 48% for inviscid carangiform swimmers, that is trout-like swimmers [48], and 34% for stingray swimmers [40].…”