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Chapter 2 - State of the art
ORLANDI & LEONARDI (2000) carried out numerical simulation of wall bounded flows and
showed how a change of the boundary conditions near the wall brings about changes in the near
wall turbulence structure. Of interest is the case of flow past cavities, typical of rough walls.
RHODES & SENIOR (2000) carried out a numerical study using CFD on rib roughness on side
walls of a straight channel. They replaced small and large scale roughness with an equivalent
roughness plane wall stating that the variation of equivalent roughness ( ε ) and the channel width
are independent of the rib roughness height and spacing when scaled appropriately. The tests were
performed for rather small roughness ribs (about 3 to 4 mm).
The effect of macro-roughness elements, as for example vertical ribs with a trapezoidal cross-section
on the outer vertical wall of a bend, on the process of scouring has not been investigated so
far. Furthermore the effect of wide grain size distributions on the scouring process is rarely
explored.
page 16 / November 9, 2002
Wall roughness effects on flow and scouring