Flow field UVP measurements of a Y-shape outlet structure

Y-shape outlet structures are used to release the turbine water into a reservoir. Classical design often uses a Y-shape over a certain length and with a specific opening angle. Depending on the geometry, especially in turbine mode, significant undesired flow separations may occur at the bifurcation. Investigations were performed with physical model tests using ultrasonic profilers at 1 and 2 MHz emission frequencies in order to assess an approach to control the design of an outlet structure by measuring the flow field and its fluctuations. The distribution and fluctuation of the flow velocities, both at the exit section as well as along the tunnel axes for both outlet openings of the Y-shape geometry allow detecting potential flow detachment at the bifurcation.