Dual Laser and Shadow Particle Image Velocimetry for Multiscale Fluid-Structure Interactions
Experimental Fluid-Structure Interaction (FSI) often involves phenomena that occur simultaneously across vastly different spatial and temporal scales. For example, the separation bubble behind a cylinder and the vortex interactions in its wake, or the flow produced by an individual swimmer and the flow generated by the movement of the entire swarm. Imaging-based flow studies of such FSI phenomena are challenging and often lead to separate analyses of different flow regions. This work introduces simultaneous shadow and laser-based Particle Image Velocimetry (PIV) to obtain concurrent near-wall and far-field flow velocity measurements. The experimental setup developed here enables the first simultaneous comparison between shadow- and laser-based PIV, demonstrating that shadow velocimetry can achieve accuracy comparable to laser-based measurements at the macro scale. We then use this new combined flow measurement technique to fully capture the velocity field generated by a shrimp-inspired underwater robot, employing laser PIV to record the flow surrounding the robot and shadow PIV to focus on the actuators, imaging regions that the laser technique cannot resolve due to wall reflections and shadows behind the structures. The simultaneous application of shadow- and laser-based PIV offers a new experimental avenue for gaining insights into the physics of FSI phenomena.