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Squid and other cephalopods use a form of jet propulsion that is not well understood, especially when it comes to their hydrodynamics in turbulent flow conditions. Uncovering their secrets can help create new designs for submarine robots and bio-inspired vehicles that must operate in this environment.
Researchers in Scotland, the United States and China are exploring the fundamental mechanism behind pulsed jet propulsion in squid. In Fluid physics, from AIP Publishing, the group describes their numerical study of jet propulsion of turbulent flow cephalopods considered for the first time. Among their findings, they found that thrust production and efficiency are underestimated within laminar, or non-turbulent, flows.
The model for this research is a squid-like 2D swimmer that has a flexible mantle body with a pressure chamber and a nozzle that acts as the water inlet and outlet. An external force, which mimics the constriction of the squid muscle, is applied to the flexible surface of the model’s coat.
“As a result, the internal volume of the body decreases and the water inside the chamber is ejected to form a jet stream,” said Yang Luo, one of the authors and research assistant at Strathclyde University in Glasgow, in Scotland. “The squid is pushed forward by the strong jet in the opposite direction, then the mantle automatically inflates thanks to the stored elastic energy. During the jacket inflation, the water is sucked into the chamber and is expelled during the subsequent deflation of the jacket. “
Jet propulsion can be more efficient when considering turbulent flow, according to Luo. The team also discovered symmetry breaking instabilities of the eddies around the water jet, which emits water jets, after several continuous jet cycles.
“This may help provide a better understanding of why burst-and-coast swimming is used by juvenile and adult squid operating within turbulent flows more frequently than baby squid operating within laminar flows. “Luo said.
In addition to jet propulsion, young and adult squid also rely on the swing of the fins on their heads to swim quite often. The team found that this burst-and-coast style can help squid avoid the symmetry breaking instability of the surrounding flow vortex that could cause a deterioration in thrust and efficiency.
“The results of our work on the mechanism of symmetry breaking instability provide guidance for the design of squid-inspired robots and underwater vehicles,” Luo said. “Continuous jet propulsion may not be favorable and specific measures are needed to mitigate the effect of this instability when designing submarine vehicles or jet propulsion-inspired powertrains via active body deformation control to modify the evolution of the model of internal vortices “.
Will we see new jet-propelled submarines soon?
“It’s hard to determine at this point,” Luo said. “But being a relatively less studied form of underwater propulsion, it is advantageous in terms of a simple mechanism for effective instant escape and high maneuverability. This makes it promising for integration with typical powertrain propulsion to achieve on-demand maneuverability. “
Source of the story:
Materials provided by American Institute of Physics. Note: The content can be changed by style and length.
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