عنوان مقاله [English]
Contractions have many uses in supercritical flows, such as flow conveyance from intake channels of dams to tunnel spillways, reduction of chutes width and reduction of flow conveyance time in the flood conduits. In supercritical flows shock waves form at contractions. In this research, height of shock waves in contractions of open-channels with trapezoidal and rectangular sections was investigated using experimental models. For this purpose, transition wall with the lengths of 1, 0.75 and 0.5m, convergence ratio with the values of 1/2, 1/3 and 1/4 and side slope with the angles of 35o, 45o, 60o, 70o and 90o were considered as geometric variables of the experiments. Also Froude number was assumed as a hydraulic variable of the experiments in the range of 3.25-9.23. The values of shock waves height were measured in various points of wave front. Then effect of dimensionless parameters achieved by dimensional analysis was investigated on the height of shock waves formed in the transitions. In general, the results showed that increasing the side slope angle of the transition wall, reduction of convergence ratio, and reduction of the transition wall length and increasing of the Froude number had a direct relationship with increasing the wave height. Finally, an equation with R2=0.89 was recommended using the dimensionless parameters for computing the height of shock waves at any point of contractions. Also, the results showed that the most effective parameter on height of shock waves was the length of transition wall.