Spray droplet separation from breaking foamed waves in very strong winds

Abstract

The splay droplet separation over the crests of waves may control the aerodynamic roughness of the sea surface in high winds. The spume separation for the spilling breaker is numerically evaluated by using a lattice Boltzmann model for weakly compressible multiphase fluids. Our calculations show that for the solitary wave with H=2m in the water of h=10m, splay droplet separation occurs over the crests of foamed waves and streaks on the surface for extrapolating wind speed U10 =40m/s. The limiting drag coefficient computed from averaging the tangential stress, Reynolds stress and pressure over the effective wavelength is 0.0029 at U10 =40m/s. This critical value of wind speed U10 that marks the limiting aerodynamic roughness increases up to 46m/s with increasing viscosity number Nμ defined by the fourth root of Morton number. The limiting drag coefficient also increases up to 0.0032 with increasing Nμ.