Scour around underwater unexploded ordnances (UXOs): An experimental and computational investigation

Underwater unexploded ordnances (UXOs) pose a significant threat to human health and safety as well as the environment. The understanding of the scour around UXOs is essential for remediation actions. Many previous studies simplified UXOs as cylinders. We report an experimental and computational study on the hydrodynamics and morphodynamics around a real UXO and the comparison with a cylinder. With detailed flume data and simulation results, we show the UXO shape has a great impact on the hydrodynamics and the consequent scour and burial process. The shape effects also convolute with the flow's angle of attack, making it even more important to consider the shape of UXOs. Hence, two angles of attack, 45° and 90° were investigated. The bulk behavior of scour around UXOs is akin to scour around any slender object placed on a sediment bed. However, the detailed scour process is significantly different. Our results show that flow contraction near the two ends of UXOs, recirculation behind the object, vortex shedding downstream, and jet-like flow under the object all play dominant roles during different stages of scour. In addition, we generalized the scour process around UXOs and other objects by applying a scaling analysis based on first principles of physics. A fitted saturation growth-rate equation relating scour volume and time collapses data reasonably well.