A direct numerical simulation of a fully developed, low-Reynolds-numbe
r turbulent flow in a square duct is presented. The numerical scheme e
mploys a time-splitting method to integrate the three-dimensional, inc
ompressible Navier-Stokes equations using spectral/high-order finite-d
ifference discretization on a staggered mesh; the nonlinear terms are
represented by fifth-order upwind-biased finite differences. The unste
ady flow field was simulated at a Reynolds number of 600 based on the
mean friction velocity and the duct width, using 96 x 101 x 101 grid p
oints. Turbulence statistics from the fully developed turbulent field
are compared with existing experimental and numerical square duct data
, providing good qualitative agreement. Results from the present study
furnish the details of the comer effects and near-wall effects in thi
s complex turbulent flow field; also included is a detailed descriptio
n of the terms in the Reynolds-averaged streamwise momentum and vortic
ity equations. Mechanisms responsible for the generation of the stress
-driven secondary flow are studied by quadrant analysis and by analysi
ng the instantaneous turbulence structures. It is demonstrated that th
e mean secondary flow pattern, the distorted isotachs and the anisotro
pic Reynolds stress distribution can be explained by the preferred loc
ation of an ejection structure near the comer and the interaction betw
een bursts from the two intersecting walls. Comer effects are also man
ifested in the behaviour of the pressure-strain and velocity-pressure
gradient correlations.