Data from turbulent flows over steep-sided trapezoidal trenches and a
backward-facing step in an open channel were used to assess the perfor
mance of three alternative models of turbulence viz. the industry-stan
dard kappa-epsilon model, a second-order closure which is linear in th
e Reynolds stresses and another which is quadratic in the same quantit
ies. The computations were carried out on body-fitted coordinates and
were carefully checked for numerical accuracy. It is demonstrated that
the mean-flow parameters are predicted equally well by all models but
that the details of the turbulence structure are best captured by the
second-order closures, The significance of these results to the pract
ical prediction of trench flows is discussed.