Two-phase flow modeling of the influence of wave shapes and bed slope on nearshore hydrodynamics

An Eulerian two-phase flow model (air-water) was used to simulate nearshore hydrodynamic processes driven by wave motion. The flow field was computed with the Reynolds-Averaged Navier-Stokes equations in conjunction with the Volume-Of-Fluid method and the RNG turbulence-closure scheme. To study the effects of different wave shapes on surf-swash zone hydrodynamics, a set of numerical experiments was carried out. Predictions of three wave theories (Airy, 2nd-order Stokes and 5th-order Stokes) were compared, with a focus on the turbulence and flow fields. Model performance was assessed by comparing numerical results with laboratory experimental observations. Relationships between the water depth, undertow, TKE and wave characteristics are presented. The results indicate that the characteristics of turbulence and flow, for example the position of wave breaking and magnitude of TKE, are affected by different wave types. Numerical simulations showed that only high-order Stokes wave theory predicts the nonlinearity required for predicting hydrodynamic characteristics in agreement with existing understanding of nearshore processes. Numerical simulations were run for different hydrodynamic conditions, but with a focus on different bed slopes. The transformation of incoming waves as they reach shallow water occurs closer to the shoreline for steeper profiles. Consistently, the peaks in TKE and wave set-up are shifted onshore for steeper slopes. The numerical results showed that TKE and undertow velocity are smaller on dissipative beaches than on intermediate beaches.