Unsteady Two-Dimensional Orifice Flow: An Experimental Study

Orifice flows were used as water clocks since the Antiquity up to the 16-th century. Today the sand glass uses the same principle with granular material. Orifices and nozzles are used also as measuring discharges. A related form is the sharp-crested weir commonly used for discharge measurement in open channels. Most works were conducted with steady flow conditions and there is little information on the unsteady flow pattern. In this study, the writers describe an experimental investigation of an unsteady orifice flow. The study was conducted in a large-size facility with a rectangular orifice (0.75-m by 0.07-m) discharging up to 1.2 m3 in about 10 seconds. The study is focused on the unsteady flow patterns, the discharge capacity and the velocity field in the reservoir. The results are compared with "classical" orifice flow results