Flow Structure and Slipstream Characteristics of an Axial Flow Hydraulic Turbine with a Collection Device in an Open Channel

The axial flow hydraulic turbine with a collection device can be simply installed in the flowing water of an open channel with shallow water depth to generate electricity, and the power output is increased by collecting and increasing the velocity of the flow. When the power output of this hydraulic turbine is insufficient, it is necessary to install several turbines in series with the flow in narrow channels, and it is necessary to establish a guideline for appropriate installation intervals. In this study, the relationship between the velocity distribution and the vortex structure inside and outside the hydraulic turbine was investigated by experiments and multiphase flow analysis considering free surface in order to clarify the slipstream characteristics of this hydraulic turbine in an open channel with shallow water depth. As a result, it was clarified that the axial flow velocity behind the brim recovered rapidly due to the momentum exchange between the flow passing through the outside of the hydraulic turbine and the flow passing through the inside of the hydraulic turbine. It was also discovered that all the major vortices disappeared at a position 9 times the runner diameter in the downstream direction from the runner center, and more than 70% of the axial flow velocity was recovered in the entire width direction.