Research on the Inlet Shape of Steep Diversion Tunnel by Model Test

Since the flow pattern in steep slope pilot tunnel is difficult to control,it’s critical to optimize the inlet shape.A 1∶ 85 hydraulic model test is carried out for the diversion work of a project construction.By comparing the inlet and the flow pattern in the tunnel,it’s found that elliptic top of the inlet is detrimental to the tunnel safety,in which case the upstream water level under two-stage flow conditions is reduced remarkably,but the mixed free-surface-pressure flow occurs in the tunnel under the designed diversion flow condition.The tunnel inlet with sharp edge is recommended,with which the discharge capacity,the flow pattern,and the pressure characteristics could all meet the design requirements.It can ensure that the flow in the tunnel is always free flow at all levels of diversion flow.