Hydrodynamic study of freely swimming shark fish propulsion for marine vehicles using 2D particle image velocimetry.

Mannam Naga Praveen Babu,P Krishnankutty,J M Mallikarjuna

doi:10.1186/s40638-016-0036-0

Mannam Naga Praveen Babu, P Krishnankutty + Show 1 more

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https://doi.org/10.1186/s40638-016-0036-0

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Two-dimensional velocity fields around a freely swimming freshwater black shark fish in longitudinal (XZ) plane and transverse (YZ) plane are measured using digital particle image velocimetry (DPIV). By transferring momentum to the fluid, fishes generate thrust. Thrust is generated not only by its caudal fin, but also using pectoral and anal fins, the contribution of which depends on the fish’s morphology and swimming movements. These fins also act as roll and pitch stabilizers for the swimming fish. In this paper, studies are performed on the flow induced by fins of freely swimming undulatory carangiform swimming fish (freshwater black shark, L = 26 cm) by an experimental hydrodynamic approach based on quantitative flow visualization technique. We used 2D PIV to visualize water flow pattern in the wake of the caudal, pectoral and anal fins of swimming fish at a speed of 0.5–1.5 times of body length per second. The kinematic analysis and pressure distribution of carangiform fish are presented here. The fish body and fin undulations create circular flow patterns (vortices) that travel along with the body waves and change the flow around its tail to increase the swimming efficiency. The wake of different fins of the swimming fish consists of two counter-rotating vortices about the mean path of fish motion. These wakes resemble like reverse von Karman vortex street which is nothing but a thrust-producing wake. The velocity vectors around a C-start (a straight swimming fish bends into C-shape) maneuvering fish are also discussed in this paper. Studying flows around flapping fins will contribute to design of bioinspired propulsors for marine vehicles.

Highlights

Aquatic animal propulsors are classified into lift-based, undulation, drag-based and jet mode
Past researchers [7,8,9,10,11,12,13,14,15,16,17,18] carried out experiments on hydrodynamic studies of fish locomotion as well as maneuvering by using particle Image velocimetry (PIV) system
In sub-carangiform swimming fish, the thrust is developed by the rear part of the body and the tail fin

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Aquatic animal propulsors are classified into lift-based (e.g., penguins, turtle forelimb propulsion and aerial birds), undulation (e.g., fishes, eels), drag-based (e.g., duck paddling) and jet mode (e.g., jelly fish, squids). Fishes generate thrust by using its tail fin, paired fins and its body. A shark fish which belongs to the sub-carangiform is kept in a glass tank (Fig. 1) and the water particle kinematics around its tail and fins are observed using a two-dimensional PIV system while the fish try to swim forward. The sub-carangiform fishes can move its caudal fin at a higher amplitude compared with form of fishes, resulting better thrust generation. That is the reason for choosing this form of fish for the present study It moves forward by flapping its caudal fin and body undulation. There are positive and negative pressure regions along the body The fluctuations of these pressure distributions result in a propulsive force, pushing the fish forward. The above equation is the simplest case of pure translation motion normal to a free stream Vo [19]

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