T A numerical wave flume is constructed based on the Reynolds Averaged Navier-Stokes (RANS) equations with turbulence closure by a modified k-ε model to study the viscous interactions of waves with vertical breakwaters for different overtopping cases.The governing equations,the turbulence model,boundary conditions,and solution method for the numerical wave flume axe introduced briefly.The reliability of the numerical wave flume is examined by comparing the numerical results with the experimental measurements,and good agreements between them indicate,the validity of the present model.The developments of mean velocity fields,the contours of vorticity,and the influences of wave nonlinearity on turbulence field as wave passing through vertical breakwaters are discussed in detail based on the numerical results.It is noted that the vortices at the rear of the lower submerged breakwater are close to the bottom and maybe induce the scouring to the leeside toe of marine structure in practice.Over all,a conclusion can be obtained from this study that the turbulence in wave field around structure is induced directly by the development of boundary layer on the solid boundary,the nonlinear interaction of free surface with obstacle,and the plunging of overtopping waves.