The influence of three-dimensional flow behaviour in quasi-two-dimensional water impacts of rigid wedges

Water impacts form the critical load case for the outer hull panels of small high-performance marine craft. This is a complex case of fluid–structure interaction, where the severity of the impact depends on geometric and environmental conditions. To investigate such impacts, a commonly used simplification is to reduce the three-dimensional hull form to that of a two-dimensional wedge, which may be investigated using experimental methods. Such experiments incorporate features that restrict flow in the third dimension, thereby promoting a quasi-two-dimensional flow environment. However, due to the practicalities of real-world testing environments, no impact is completely two-dimensional; some fluid is always ejected normal to the wedge cross-section. The influence of three-dimensional flow within quasi-two-dimensional experimental setups is poorly understood, and often assumed to be negligible. In this work, numerical methods are used to study the influence of flow restriction and three-dimensional behaviour on the resulting forces and pressures of a constant-velocity water impact of a rigid wedge. Results indicate that even small degrees of three-dimensional behaviour result in substantial deviations in maximum force and pressure relative to a purely two-dimensional impact. For a wedge with a 10 ° deadrise, a spanwise clearance of 1.0% of the wedge’s span results in an 8.1% decrease in maximum impact force. Wedges with a larger deadrise angle are less sensitive to the introduction of three-dimensional flows brought on by decreased flow restriction. A semi-empirical formula is proposed to relate reductions in maximum impact forces with a wedge’s deadrise angle, aspect ratio and the degree of flow restriction. These results indicate that flow restriction should be considered when interpreting measurements from quasi-two-dimensional experimental test setups.