Flow sensing of a solid plate in the wake vortex street

Understanding the mechanisms by which fish sense vortical perturbations is crucial for both biological insights and technological advancements. We investigate the hydrodynamics of a solid plate moving vertically through the reverse Kármán vortex street generated by a horizontally moving flexible flapping plate in a viscous flow. The impacts of the horizontal distance between the two plates (D) and the moving speed of the solid plate (vy) are considered. The horizontal distance determines the vortical environments, i.e., whether the solid plate impinges through the vortex cores or the gaps. Different vortical environments exhibit varying vortex-induced velocities, resulting in distinct force and pressure patterns on the solid plate. The evolution of these sensed forces and pressures is mapped along the path of the solid plate, suggesting a potential mechanism by which fish detect the position and properties of surrounding vortices. Furthermore, it is found that increasing speed can amplify the sensed force and pressure signals by thinning boundary layers and strengthening friction force. Nevertheless, the established mapping relationships remain applicable across varying velocities, and a scaling relation has been derived to normalize this amplification effect on the vertical force. These findings enhance our understanding of fish sensory mechanisms and could inspire innovative designs and control strategies for underwater vehicles.