Pressure, velocity and boundary layer distributions on an embankment weir.

Stefan Felder

Tuesday 30 june 2015

9:00 - 9:15h at Africa (level 0)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation

Parallel session: 4F. Engineering - Instrumentation

Physical experiments were conducted on a large size embankment weir with upstream and downstream ramps of 1V:2H and rounded corners for a range of flow conditions 0.042 _ H/Lcrest < 0.321 corresponding to flow rates of 0.011 _ Q _ 0.226 m3/s. The experiments highlighted non-hydrostatic pressures and a rapid redistribution of velocities at the upstream and downstream ends of the crest. At the downstream end negative pressures were observed for the largest flow rates indicating a risk of cavitation. Both velocity distributions and free-surface profiles showed some self-similarity. A turbulent boundary layer developed at the upstream crest edge and the growth of the boundary layer properties was in close agreement with the smooth turbulent boundary layer theory. The bed shear stresses were calculated on the crest and a close agreement of average dimensionless bed shear stresses were observed for the law of the wall and the momentum integral methods (_/(_ g H) _ 0.0018). The dimensionless discharge coefficients of the present experiments were best correlated splitting the data into long- and broad-crested weirs. The present discharge coefficients were in close agreement with previous broad-crested weir studies with upstream rounded corners. The increase of the discharge capacity of a broad-crested weir is best achieved through the rounding of the upstream corner rather than the design with an upstream slope.