Flapping to the Surface: Free Surface Effects on a Manta Ray-Inspired Panel*

Taking inspiration from manta rays - naturally great swimmers - can allow human-made devices to operate with greater efficiency. In this talk, a shape-changing panel is used to model a manta ray fin, by two rows of actuating tubes. Unsteady flapping motions and shape change of the panel will be implemented in calm water at different depths from the free surface. Forces, panel shape, input motions, and fluid features will be measured and reported. In this phase of experiments, the shape change of the panel was prescribed and then the panel was subjected to an unsteady flapping motion. With only one row of tubes actuated, the maximum force decreased as the panel was flapped at increasing depths from the free surface. However, when subjected to dual actuation, or an increase in panel stiffness, the maximum force stayed relatively constant at increasing depths. At close distances to the free surface, the tip of the panel is attracted to the free surface due to low pressure, which is seen in a greater deflection toward the free surface. The knowledge gained from this study will be extended by testing a manta ray model in a towing tank where both horizontal and vertical motions can be prescribed along with shape change.