Weirs placed obliquely in a shallow flow

Abstract

    This report is the conclusion of a series of experiments, which were performed on weirs placed obliquely in a shallow flow. Its purpose is to report on laboratory investigation on the flow over different types of oblique weirs, including behaviour and hydraulic characteristic of the flow, different phenomena in the neighbourhood of the weir, hydraulic parameters and physical laws that govern the process. Two different types of impermeable weirs, a rectangular sharp-crested weir and a rectangular broad-crested weir, both placed 450 obliquely to the flow direction, were tested under various flow conditions. Flow velocities were measured using PTV - Particle Tracking Velocimetry technique. In conjunction with Matlab we can get almost necessary statistical information. This report also aims at a quantitative view on the energy loss and the discharge coefficient. Various phenomena like vortex, hydraulic jump, undulation, flow divergence, flow concentration, etc. were observed. It was shown that the flow tends to change its direction to - 9 - perpendicular direction with the weir crest, and causes different flow behaviours, namely the difference in water levels at two ends of the weir, the flow concentration at on one side of the flume behind weir, and the variation in flow velocity distribution. Generally speaking, the hydraulic phenomena that happen to a broad-crested weir are similar to those occur in the neighbourhood of a sharp-crested weir, although there are some remarkable differences