  This paper presents numerical simulations of a bichromatic wave group
propagating and breaking over a fixed breaker bar. The simulations are
performed using a newly stabilized Reynolds-averaged Navier Stokes (RANS)
two-equation turbulence closure, which solves the longstanding problem of
over-production of turbulence beneath surface waves in the nearly potential
flow region prior to breaking. This model has previously been tested on
small-scale spilling breaking regular waves, whereas in this work focus is on
full (rather than model) scale application, wave groups (rather than regular
waves) and plunging (rather than spilling) breakers. Additionally this paper
has novel emphasis on bottom boundary layer dynamics which are very important
for cross-shore sediment transport predictions. The model is validated by
comparing with results from a previous experimental campaign. The model is
shown to predict the surface elevations, velocities and turbulence well in the
shoaling and outer surf-zone, avoiding turbulence over-production and incorrect
undertow structure typical of standard turbulence closures. Comparison with
detailed boundary layer measurements in the shoaling position reveals that the
model is able to accurately capture the temporal dynamics of the entire wave
boundary layer, including evolution of the boundary layer thickness, velocity
overshoot and phase-shifts. Comparison in the surf zone additionally reveals
that the model is able to accurately capture the transport of breaking-induced
turbulence into the wave boundary layer. The performance of the model indicates
that it can be used directly in the simulation of cross-shore sediment
transport and morphology and also be used to study important hydrodynamic
processes, which can help improve the predictive skill of morphodynamic profile
models applied in coastal engineering.
