Experimental study of the effect of different sill geometry on hysteretic behavior of supercritical regime

Hysteresis during supercritical flow is an issue that is not well understood. It occurs near structures in water supply systems, water transmission lines, and channels. The hysteretic behavior of a flow causes different states in the flow for otherwise identical conditions. (Defina and Viero, 2018) investigated the behavior of supercritical flow near a vertical gate. They proposed a theory for predicting hysteresis in the vicinity of a gate based on the Froude numbers upstream and downstream of the gate as well as on the gate opening ratio. Their results also confirm the existence of hysteretic behavior of the flow. The experiments also confirmed the validity of the theory on the effect of upstream and downstream Froude numbers on hysteretic behavior. (Defina and Viero, 2010) examined the various states created by the flow in a gradual narrowing. They showed that the friction and slope of the channel floor affect the stability of the flow and can create different hysteretic loops.The main purpose of this study was to investigate the contradictory behavior of supercritical flow with a sill located in the flow path and with different geometries. The existence of such contradictory behavior occurs due to hysteresis, for which there are relatively limited studies. Generally, the occurrence of hysteresis at the collision of the flow with the obstacle is expected. As for the same input current, two different behaviors are observed that behavior depend on the flow cycle. The flow cycle means increasing the discharge to a certain value and then decreasing it to the initial discharge.