Effect of bed dunes on spatial development of open-channel flow

Abstract

The spatial development of turbulent, sub-critical open-channel flow over five identical dunes is studied by the numerical solution of the RANS equations utilizing theVOF free-surface formulation and the k–e or Spalart–Allmaras turbulence models. Results are presented for smooth and rough walls and several dune dimensions. One of the cases was also studied experimentally. The flow separation at each dune crest generates a recirculation in the dune lee-side and reattachment at a distance, which increases with increasing dune height and decreasing dune length. Turbulence does not fully develop over the dunes, while the majority of turbulent kinetic energy production takes place in the recirculation region. The spatially mean, free-surface level decreases in the flow direction over the dunes, while the free-surface amplitude increases with increasing dune height. The dune drag coefficient increases with increasing dune height, while the contribution of form resistance on the drag increases with increasing dune height and decreasing dune length.

Keywords:

• Bed dunes
• open channel
• RANS equations
• turbulent flow
• VOF method