Exploring forward and backward swimming dynamics in bioinspired undulatory swimmers

This research devises a sophisticated numerical model for bioinspired underwater vehicles, drawing inspiration from the locomotion of natural aquatic creatures, including both forward and backward swimmers. This model features a rigid head equipped with a heave, pitch actuation, and a passive flexible tail, operating effectively under quiescent flow conditions at a Reynolds number of $Re=100$. An exhaustive exploration of different tail flexibility and head actuation parameters has been undertaken, leading to the observation of a diverse range of wake patterns, from a downward wake to an upward wake, and even revealing the formation of a unique bifurcated wake. The findings indicate that when tail rigidity is set at $gamma=1.0$ and head actuation parameters are defined with a pitching amplitude $Theta_0=pi/8$ and a heaving amplitude $h=0.3$, and vortices shed from the tail create a downward jet. In contrast, at $gamma=0.5$, vortices are released from both the head and tail, moving upward and downward trajectories. Decreasing the bending rigidity to $gamma=0.2$ with $Theta_0=pi/8$ and $h=0.1$ results in the creation of successive vortices on alternating sides of the mean swimming path, forming a single upward jet similar to the motion observed in backward swimmers. Intriguingly, at $gamma=0.2$ with $Theta_0=pi/8$ and $h=0.3$, a dipole couple is generated in each half cycle, moving towards the head at an inclined angle, thereby resulting in a distinctive bifurcated wake structure.