Application of PIV-based pressure measurements to the study of aquatic propulsion

Although it is relatively straightforward to image how fluid moves around a swimmer, translation of these motions to mechanisms that generate forces for propulsion is more difficult. This process is greatly facilitated by a recently developed technique for non-invasive pressure measurements that generate 2D pressure fields. Here, we explore how accurate a purely pressure-based calculation of propulsive forces can be. By comparing these calculations to forces and torques measured directly using a sensor on a robotic flapping foil system, we characterize the effects of motion frequency and out-of-plane flows on the calculation's accuracy. We then apply this calculation to study the dynamics of fish-like swimming of a foil model with non-uniform flexural stiffness, and to those of a freely swimming fish.