With their flexible, flattened shape, rays are some of the most efficient swimmers in the ocean. But, at first glance, it seems as if their protruding eyes and mouth would interfere with that streamlining. A new study uses computational fluid dynamics to tackle the effects of these protrusions on stingray hydrodynamics.
With their digital stingrays, the team found that the animal’s eyes and mouth created vortices that accelerated flow over the front of the ray and increased the pressure difference across its top and bottom surfaces. The result was better thrust and the ability to cruise at higher speeds. Overall, the ray’s eyes and mouth increased its hydrodynamic efficiency by more than 20.5% and 10.6%, respectively. The lesson here: looks can be deceiving when it comes to hydrodynamics! (Image credit: D. Clode; research credit: Q. Mao et al.)
Richard Bready
A very elegant confirmation of a possibility mentioned by Steven Vogel in a book we both like, Life in Moving Fluids, page 50: “More interesting, though, is the suggestion that the eye of an ordinary bony fish is located at the point where pressure changes caused by swimming are least. This arrangement should keep the focus of the eye minimally sensitive to speed-dependent pressure changes.”
Especially elegant for adaptive design to lower pressure by accelerating flow, two benefits at once; perhaps the flexibility of cartilage makes it more sensitive to pressure than bone?