A study of the flow field of an axial flow hydraulic turbine with a collection device in an open channel

Axial flow hydraulic turbine with a collection device aims to improve the output using an open channel and concentrating/increasing the volume and velocity of flow. The flow field of this turbine is extremely complex because it has a free surface, and its internal and external flows are mixed. Several such hydraulic turbines are occasionally placed in series against a flow. Thus, it is of utmost importance to elucidate the flow structure downstream of the hydraulic turbine. The proposed study aims to elucidate the flow field of this hydraulic turbine in a shallow open channel by the means of PIV measurement, multiphase flow analysis considering the free surface, and single-phase flow analysis considering uniform flow as the premise. As a result, the characteristics of the flow field of the hydraulic turbine considered herein in an open channel are clarified. Especially, in terms of the slipstream characteristics, it is clarified that due to the influence of free surface and channel bottom, the type of vortexes that occur downstream of the hydraulic turbine are different, and the process and distance of velocity recovery differ depending on the vortex.