Water column impact on a rigid wall with air cavity effects

Abstract

Water column impacts on a rigid wall without and with air cavity entrapment are investigated based on potential-flow theory without considering the gravity effect. A boundary element method is employed to simulate the entire hydrodynamic process, with an introduced decoupling technique of a shallow-water approximation to tackle the thin jet difficulty in impact problems. Numerical techniques to deal with processes including the cavity jet impingement and fluid immersion are also introduced. Numerical simulations are carried out for water column impact processes with cavities of different volumes, shapes, and initial pressures inside. Theoretical deductions are performed for the limiting case of impact without air cavity at the initial and steady state. From the energy point of view, an energy transfer relation is established to achieve a quantitative prediction of the maximum pressure in a deforming cavity in a general impact process. Quantitative analysis is made to assess the effects of the initial nondimensional potential energy of the cavity on the maximum cavity pressure during the impact. Interesting phenomena such as the inner jet generated away from the impact surface are observed and discussed.