Jet-cavity coupled flow and deformation behavior of hollow disc during high-speed water entry

A bidirectional fluid-structure interaction simulation is conducted to investigate the high-speed water entry of a hollow disc. A hollow disc refers to a disc that has an internal space, which alters the behavior of cavity evolution, jet flow, and structural deformation. The results indicate that the cavity of the hollow disc exhibits a spherical cavity shape and connect smoothly with the jet. The head of the jet presents a spherical droplet shape, which then gradually transitions into an elliptical form. The hollow disc experiences significant fluid force, causing the velocity to decrease rapidly, and its displacement undergoes noticeable inflection simultaneously. The hollow structure effectively alleviates the severe force concentration of a solid disc. Notably, this study also reveals a series of key phenomena: a disc that is only externally closed has a cavity contour similar to a hollow disc, while its jet evolution is similar to a solid disc. The cavity depth profoundly alters the jet-cavity evolution and deformation behavior of the hollow disc. A larger cavity depth results in larger cavity sizes, but simultaneously causes the cavity walls below the disc to exhibit more fluctuating shape.