Numerical study on the fluid dynamics for tandem water entries of two cylinders

Abstract

A three-dimensional numerical model is established to simulate the tandem water entry at different time intervals between two cylinders. The evolution of cavity, pressure field, velocity field and multi-scale vortex structures during water entry are studied. The motion characteristics of the tandem cylinders are analyzed to investigate the coupling effect of the flow field. Numerical results show that the water entry of the first cylinder significantly changes the flow field distribution, resulting in the complex flow field coupling evolution and the decrease of impact load on the trailing cylinder. For a time interval of 1.8 ms or 2.8 ms, the trailing cylinder enters the first cavity and then accelerates to catch up with the first cylinder under the effect of the pressure difference until collision. As the time interval increases to 4.8 ms, the trailing cylinder experiences a lower drag and forms a conical cavity, decelerating with a small deflection tendency. Moreover, cavity evolution is accompanied by the formation and dissipation of vortices and the vortex structures of tandem cylinders affect each other in different degrees.