Steady flow over a 2D backward facing step

This canonical case is based on the description by Driver and Seegmiller

    D.M. Driver and H.L. Seegmiller. Features of a reattaching turbulent shear
    layer in divergent channel flow. AIAA Journal, 23(2):163–171, 1985. 

where the mesh is based on the Langley Research Center Turbulence Modeling
Resource set-up provided at:

    https://turbmodels.larc.nasa.gov/backstep_val.html

The Reynolds number based on the step height is Reh 36000 for which the
stated reattachment length is at 6.26 +/- 0.1 x/h

The Allrun script will run the case and generate graphs showing the wall
shear stress and velocity profiles at various cross-sections.

For further information please visit:

    openfoam.com/documentation/cpp-guide/html/verification-validation-turbulent-backward-facing-step.html

