Experimental study of hydrodynamic forces acting on artificial fish in a von Kármán vortex street

The present paper describes the hydrodynamic forces acting on different sized fish-shaped objects in a von Kármán vortex street, where in a wake of an object a specific locomotion pattern, Kármán gaiting, is observed. The present paper investigates the hydrodynamic forces, both lateral force and torque on a passive fish-shaped body in those hydrodynamic conditions. By using a range of fish length to wake wavelengths, size matters were experimentally tested for balancing the forces on an artificial fish intercepting oncoming vortices, potentially to exploit the lateral and rotational elements in the flow that may facilitate Kármán gaiting in a biological fish. To do this, five artificial fish were manufactured to mimic a rainbow trout (Oncorhynchus mykiss), were inserted into the flow tunnel and recorded simultaneously the hydrodynamic forces and DPIV images. The experimental results found that the hydrodynamic forces supporting Kármán gaiting did not stop even if the body length of the fish-like object exceeded the wake wavelength. Overall, the obtained results help to understand fish and fluid interactions when swimming in the Kármán vortex street.