Simulation of Breaking Waves in the Surf Zone using a Navier-Stokes Solver

A Navier-Stokes solver with a k — w turbulence model is used for simulating spilling breakers in the surf zone. Two different numerical techniques for describing the free surface are investigated. First, a surface tracking approach is applied, using a height function description of the free surface and a time-depending curvilinear grid being adapted to the free surface at every time step. Secondly, a VOF method is employed where a scalar field is introduced to divide grid cells into fluid and void cells and the grid is fixed in time. The time evolution of the turbulence model quantities being subject to the straining motion of wave orbital motion is analysed, and an unstable parameter region is found. After having removed the instability by an ad-hoc modification of the turbulence model, the VOF-method shows good agreement with measurements with respect to the elevation statistics and flow kinematics, while agreement of the turbulence intensities with measured values is reasonable. The present moving grid approach does not describe correctly the flow kinematics in spilling wave breaking, and consequently this approach fails in predicting wave elevation profiles on-shore of the breaking point.