Experimental Study of Unsteady Transcritical Flow Characteristics in Rectangular Channels

Document Type : Research Article


1 Irrigation and Reclamation Engineering Department, University of Tehran

2 Dept. of Irrigation and Reclamation Eng., University of Tehran, Karaj, Iran


The occurrence of transcriticalor mixed flow, i.e., supercritical and sub critical flow regimes, is considered as a special case of unsteady flow in a channel reach, which can clearly be exemplified by a moving hydraulic jump. Some complexity is inherent in the numerical analysis of transcritical flow and published experimental data regarding this kind of flow are rarely available. In this research an experimental setup was prepared to compile the hydraulic characteristics of transcritical flow in a rectangular flume. The flume was equipped with a sluice gate at the upstream boundary. Each inflow hydro graph generated unsteady supercritical flow regime at the downstream side of the sluice gate and formed a moving hydraulic jump along the channel. During each run, the water surface profile was continuously recorded using a pressure transducer. Based on the recorded data, some flow parameters such as flow depth, pressure head and energy head were determined. The result reveals specific relations between the discharge and moving hydraulic jump parameters. Also, by applying proper assumptions and employing steady state momentum and energy equations simple yet reasonable (and time independent) relations were obtained, that determines the pressure head in subcritical region of unsteady mixed flow. Consequently, having the discharge variation as a boundary condition, one may reliably determine the unsteady transcritical flow parameter based on time independent relations.