A methodology, called large-wave simulation (LWS), is presented for the num
erical simulation of free-surface Hows past the appearance of spilling brea
kers. LWS is designed to resolve only the large, energy-carrying scales of
the How and model the effect of the subgrid, small-wavelength scales of the
flow spectrum. This part of the spectrum includes the characteristic froth
y whitecaps associated with spilling breakers. Modeling in LWS is based on
the consistent application of spatial filtering on both the velocity field
and the free-surface elevation. The subgrid scale (SGS) effect is modeled b
y two sets of stresses. (i) the eddy SGS stresses, which are identical to t
he ones arising in large-eddy-simulation of Hows without a foe surface, and
(ii) the wave SGS stresses, which incorporate the free-surface effect. Bot
h SGS stresses are modeled by eddy-viscosity models with constant coefficie
nt. The methodology is applied on two free-surface flows: (i) the interacti
on of a plane gravity wave with a surface wake layer, and (ii) the nonlinea
r evolution of a surface shear layer instability. A priori and a posteriori
tests show good agreement between the proposed model and actual SGS stress
es, while LWS of both hows successfully continue past the breaking point as
opposed to corresponding direct numerical simulations. For the first flow,
LWS predicts the postbreaking appearance of a recirculating flow region in
the wake of the breaker in qualitative agreement with experimental observa
tions. (C) 2000 Academic Press.