## Description |

Simulation of flow over a backward-facing step.

The mean velocity profile obtained from a boundary layer simulation by Spalart (1986) is
imposed at the inlet at = 667.
Random velocity fluctuations *u'*, *v'*, and *w'* are superimposed on
this profile according to a variant of the method of Lee et al. (1992). The fluctuations
are prescribed such that, at the inlet, the turbulence intensities and Reynolds shear
stress of Spalart's data are also duplicated. A convective boundary condition (Pauley et
al., 1988) is imposed at the exit. The streamwise domain consists of an entry section of
length l0*h* prior to the step and a 20*h* post-expansion section, where *h* is the step height.
The vertical dimensions before and after the expansion are *W _{1}* = 5

The Reynolds number, based on *h* and the mean inlet free stream
velocity *U _{0}*, is

The above figure shows contour plots of the instantaneous spanwise vorticity
on a typical vertical plane. The vorticity is
normalised by *U _{0}/h*. A free-shear layer spreading from the step and
interacting with the lower wall near the mean reattachment
location,

The basic statistical quantities are compared to results from concurrent experiments by
Jovic and Driver. In 1991, they conducted a backward facing step experiment at
*Re _{h}* = 6800 and

## Simulation Details |

The Navier-Stokes equations are discretized using a finite difference method on a
staggered mesh. Uniform mesh spacing is applied in the streamwise (*x*) and spanwise (*z*)
directions. In the vertical (*y*) direction, non-uniform mesh is employed with mesh
refinement at the wall and near the step. The fractional step method from Le and Mom
(1990) is used for time advancement. The Navier-Stokes equations are first advanced using
a second-order semi-implicit method without the pressure terms. The pressure is calculated
by solving the Poisson equation, and the velocities are then corrected to satisfy the
continuity equation.

The spanwise dimension is 4*h* where periodic boundary conditions are imposed. i
The simulation uses 770 × 194 × 66 grid points in the streamwise, wall
normal, and spanwise directions, respectively.

The computation uses 13 megawords of memory and requires approximately 55 CPU seconds per time step on a single processor CRAY Y-MP at a rate of 186 mflops. Statistical quantities are averaged over the spanwise direction and time. About 1100 CPU hours were required to obtain an adequate statistical sample. The total computational time corresponds to approximately 4.5 flow-through times.

## Available results |

## Previous and Reference Numerical Solutions |

## References |

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