A numerical wave tank with large eddy simulation for wave breaking

Abstract

A three-dimensional (3D) numerical wave tank (NWT) is developed based on OpenFOAM. The propagation and breaking of waves with a moderate wavelength that could be generated in the laboratory are studied. The wave periods range from 0.5 to 1.79 s and wave steepness goes up to 0.05. The volume of fluid method (VOF) is employed for interface capturing. The relaxation zone method is implemented for wave generation and absorption at the boundaries. Computationally significant factors like grid size, relaxation weight and time step are investigated to find the optimal parameters of the numerical models for various wave regimes. A relationship between grid size and time step, similar to the wave dispersion relation, is found. The accuracy and performance of the NWT are assessed through the reflecting coefficient, wave damping and phase distortion rates. Simulation conditions are monitored to achieve an error rate of less than 3%. To mitigate the effects of numerical errors on the calculation of the reflection coefficient, a modified version of Goda's approach is proposed. The coefficient of wave reflection at the outlet boundary calculated by the conventional Goda's method is as high as 4.3%. This value can be modified to be less than 2% after utilizing the revised Goda's method. Turbulent flows, especially for the breaking wave regime, are investigated by large eddy simulation. A one-equation sub-grid eddy viscosity model, with coefficients being derived from local flow properties, is employed for turbulence closure. A case study of wave breaking on a fixed bar is simulated. The validation of this NWT model is confirmed by comparing the numerical results with experimental data.