Flow around a bent plate near the free surface

Previously, we discovered that semi-aquatic whirligig beetles (Gyrinidae) display rapid, seamless diving from the free surface to underwater by bending their rear abdomen during swimming. Such morphological change of their body resulted in overall body torque in the favorable direction of diving. To understand the hydrodynamic contribution of the bent abdomen to diving, we quantitatively investigate the flow field around a mechanical model mimicking the bent abdomen and the pinned free surface using particle-image velocimetry (PIV).