Burst-coast swimming technique informs research on hydrodynamics

Fish and marine animals have long inspired scientists and engineers when researching fluid dynamics. Using an intermittent swimming method, some fish swim in a combination of active bursts and then passive coast as if gliding through the water. This specific swimming technique known as intermittent swimming, or burst-coast swimming, is energy efficient and has hydrodynamic benefits.

Researchers Jaeha Ryu and Hyung Jin Sung study this method of swimming in an effort to apply its benefits to future hydrodynamic designs and engineering strategies. To do so, they considered a burst-coast swimmer with a simple self-propelled plate and used the immersed boundary method to simulate the interactions between the fluid and the structure of the swimmer.

“The main idea is to add a momentum forcing into the N-S equations which is applied near the immersed boundary to mimic the no-slip condition,” said Sung, referring to the Navier-Stokes equations used in their calculations. “There is no need to generate the grid conformal to the boundary and the original N-S solver can be easily applied.”

The authors discovered the optimal propulsion mechanism for this form of swimming and characterized its physical parameters. As well, they found that intermittent swimming can save more than 20% of energy over a given distance.

The relationship between the flapping of a fish’s fins was also considered when the author’s examined swimming efficiency.

“The intermittent swimming saves fish energy by taking advantage of the viscous boundary layer thinning mechanism,” said Sung. “A fish can reduce its overall skin friction drag by interspersing a burst phase with a coast phase.”

Source: “Intermittent locomotion of a self-propelled plate,” by Jaeha Ryu and Hyung Jin Sung, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5126147 .