Numerical mechanism of pressure oscillations in high-resolution VOF interface-capturing scheme: Insights from wedge water entry

Numerical simulation of violent free surface flows has become increasingly important in marine hydrodynamics, where the Volume of Fluid is widely used. To maintain a sharp and bounded interface, compressive schemes such as the high-resolution interface-capturing scheme are typically employed. However, periodic oscillations in impact loading have been observed in numerical water entry simulations, a phenomenon that remains insufficiently understood. This paper investigates the numerical mechanism of pressure oscillations arising during the wedge water entry process within a finite-volume discretisation framework. The results reveal that the mechanism is attributed to the abrupt variations in mass flux and velocity difference between adjacent cells triggered by the numerical transition in the VOF interface-capturing discretisation scheme from pure downwind to a blended upwind–downwind formulation, thereby causing momentum imbalance and directly influencing the pressure gradient. Since the oscillation frequency is governed by the time for the advancing water jet root to cross single computational cells, depending on entry velocity, grid size, and deadrise angle, a simplified preliminary approach is proposed to assess their potential influence on hydroelastic coupling. Understanding the periodic pressure oscillations is essential for ensuring the accuracy of impact load predictions in both CFD-based direct strength assessments and FVM–FEA coupled dynamic response analyses. • The numerical mechanism of pressure oscillations during wedge water entry is systematically investigated. • Oscillations originate from momentum imbalance caused by abrupt variations in mass flux and velocity between adjacent cells. • The mechanism is associated with the transition from pure downwind to blended upwind-downwind VOF discretisation. • A simplified approach is proposed to preliminarily evaluate the oscillations' effect on hydroelastic coupling. • Understanding periodic loading oscillations is essential for accurate impact load prediction.