Numerical simulation of two-phase flow for wave propagation/breaking near submerged and vertical breakwaters

Monday, 15 December 2014
Roham Bakhtyar, Univ of North Carolina, chapel hill, NC, United States; US Army Corps of Engineers, Coastal and Hydraulics Laboratory, Jacksonville, FL, United States, Christopher E Kees, US Army Corps of Engineers, Coastal and Hydraulics Laboratory, Vicksburg, MS, United States, Matthew W Farthing, US Army Corps of Engineers, Vicksburg, MS, United States and Cass T Miller, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
Submerged breakwaters avoid the generation of major reflected waves that affect the beach. They are very useful for erosion control and beach protection by decreasing the wave heights. In addition, standing waves can play a significant role in hydrodynamics near the vertical breakwater. However, an accurate understanding of the wave propagation/breaking over a submerged breakwater, and wave overtopping in front of a vertical breakwater has yet to be achieved. A 2D two-phase flow model for air–water flow simulation near the submerged and vertical breakwaters is described. In the submerged breakwater case, wave propagation, wave breaking, and runup and rundown of waves on sloping beach is studied numerically with an emphasis on air-water interaction and hydrodynamic characteristics. For the vertical breakwater case, a two-phase flow model of wave breaking/overtopping hydrodynamics under fully and partially standing waves is developed and evaluated. The model contains the Navier–Stokes equations for both air and water phases, the LES turbulence closure model and a hybrid level set/volume-of-fluid approach. The numerical model is discretized using a finite element method. The model’s convergence as a function of grid refinement is examined. The numerical model is validated alongside the two experimental data sets, with good agreement found. The numerical results show that a vortex forms when waves spread over a submerged breakwater. The numerical results also indicate that the maximum turbulent kinetic energy, velocities and viscosity occur on the top of breakwater. The results show that for fully standing waves, velocities and wave height are higher in comparison to the comparable partially standing wave case (for the vertical breakwater). These calculations are in overall agreement with earlier observations, while the numerical model describes the water and air phase characteristics in greater detail than current measurements. The model provides a valuable method to advance mechanistic understanding of hydrodynamic characteristics near the breakwater in the nearshore area.