  The models that are based of fractional derivatives should be highlighted
among promising new models to describe turbulent fluid flows. In the present
work, a steady-state flow in a duct is considered under the condition that the
turbulent diffusion is governed by a fractional power of the Laplace operator.
To study numerically flows in rectangular channels, finite-difference
approximations are employed. For approximate solving the corresponding boundary
value problem, the iterative method of conjugate gradients is used. At each
iteration, the problem with a fractional power of the grid Laplace operator is
solved. Predictions of turbulent flows in ducts at different Reynolds numbers
are presented via mean velocity fields.
