Dolphins are famous for their speed and agility in the water, which raises questions for researchers hoping to learn how to optimize propulsion in fluids.
When a dolphin swims, it flaps its tail up and down in a kicking motion. This movement pushes the water backwards, generating a flow with rotating chains of various sizes.
According to , scientists have difficulty determining how these movements combine to propel the dolphin forward.
In a new one, published in March on Physical Review Fluidsresearchers discovered that the movement is due to vortices created by the dolphin cause movement.
Scientists used large-scale numerical simulations to visualize the dynamics of these vortices over a wide range of conditions, quantifying their effect on propulsion.
“Our goal is to understand which parts of the turbulent flow help dolphins swim so quickly. Using a supercomputerwe can simulate and decompose the flow to determine which components play dominant roles”, says the first author of the study, Yutaro Motoori.
Numerical simulations revealed that the dolphin’s tail produces large-scale vortex rings that push water back and generate momentum. The vortices then create smaller ones in a process called energy cascade.
Although these smaller vortices are numerous, they contribute little to the dolphin’s forward motion.
“Our results show that the hierarchy of vortices in turbulence is essential to understanding dolphin swimming. The larger vortices are responsible for most of the propulsion, while the smaller ones are mainly byproducts of the turbulent flow,” says the study’s lead author, Susumu Goto.
This approach allowed scientists to observe the movement of fluids in detail, something that would otherwise be difficult to capture. Furthermore, as a flexible computational method was used, it was easy to perform several tests under different conditions.
“We found that our results remained unchanged over a wide range of swimming speeds,” says Motoori.
Finally, understanding the mechanics of propulsion can help guide design of underwater robots faster and more energy efficient, as well as technologies to control turbulence.
