The effects of a longfin inshore squid's fins on propulsive efficiency during underwater swimming

Underwater transportation has always been attractive for human beings. Especially, the design of an underwater vehicle with high propulsive efficiency has become a passion for many researchers and engineers. While the design of such a vehicle has been discussed for a long time, an aquatic animal, namely a longfin inshore squid, has been exhibiting an incredible swimming performance under water for centuries. In this study, a longfin inshore doryteuthis pealeii squid was scanned using computer tomography (CT) to capture the details of the squid's geometrical appearance. In addition, a three-dimensional model of the squid has been built with computational fluid dynamics to understand the swimming technique of a squid. Propulsive efficiencies of squid models were calculated for 0, 4 and 8 angles of attack, funnel diameters of 0.25 cm, 0.5 cm and 1 cm and Reynolds numbers of 4.6E5, 1.0E6 and 1.6E6. A longfin inshore squid illustrated nearly 80% propulsive efficiency when the model had no fins at 0 angle of attack with 1 cm funnel diameter. Therefore, it was noted in this study that the use of larger funnel diameter, swimming with a smaller angle of attack and absence of fins provided better propulsive efficiency.