Free flow over and under cylindrical weir-gates with a flow extender

Abstract

ABSTRACT The complex field of free flow around a cylindrical weir – gate with and without a flow extender is investigated experimentally. The effects of the gap between the channel bed and the cylinder on the discharge characteristics of the cylindrical weir-gate are studied. It is observed that the ratio of the gate to weir discharge increased non-linearly with the normalized opening height. Four triangular downstream extensions of the cylinder oriented at, θ = 0, 10, 20, and 30 degrees were tested, and the minimum underflow to overflow discharge ratio was observed for θ = 10°. The highest improvement in discharge coefficients was 16% ± 6% for extender orientation angles of θ = 10°. The effects of opening height and extender angle on flow streamlines, pressure distribution, vortex strength, turbulent kinetic energy, and Reynolds stresses were investigated. A region of negative pressure was observed near the weir crest and the peak negative pressure increased with the opening height. The size and orientation of downstream wakes were measured, and it was found that the length of wakes varies from 0.30 to 1.06 times the diameter of the cylinder. The experiments showed that for a constant normalized opening height, the vortex center point formed further downstream as the upstream water head increased.