Experimental and Theoretical Investigation of Vertical Drains with Radial Inflow

Effect of tank size on the radial flow from a large cylindrical tank into a vertical drain was studied experimentally. Different flow regimes are distinguished and the factors that caused these differences are discussed. Firstly, a weir flow regime occurred, in which the coefficient of discharge varied linearly with the ratio of the water depth to the outlet diameter. Then, a transition flow was observed for larger tank diameters. It was then followed by the full-pipe flow regime. In the weir flow regime range, some gulping was observed that resulted in the production of circulation. This could lead to an orifice flow regime or a filling and emptying process that produces different water depths for the same discharge. It is shown that the application of the principle of maximum discharge and vortex theories can predict the head-discharge curves for cases in which the control section was at the entrance or end of the vertical outlet pipe. A critical ratio of the air core to the outlet diameter was found corresponding to the maximum stage in the filling and emptying process. The water depth variation with discharge in the Harspranget Dam in Sweden in the literature was analyzed to show the importance of this phenomena in practical problems.(c) 2016 American Society of Civil Engineers.