In order to study the characteristics of the different formed free surface vortices at vertical hydraulic intakes, three sets of experiments were conducted. The spiral flow was detected using the Particle Tracking Velocimetry (PTV) measurement technique in three dimensions (3D) by installing two cameras at above and side of the model. The dimensions of model were 2000mm in length, 1300mm in width and 1500mm in height. Through the experiments, extensive data including tangential (Vθ), radial (Vr) and axial (Vz) velocities and their variations with the changing vortex center in different vortex classes, were recorded and analyzed. Using the obtained results, a 3D flow path was drawn for each class of the formed vortex. Moreover, changes in the diameter of the vortex core (Dvo) in the three different classes of vortex were investigated and its changes along the vortex axis were measured. Results showed that the average of Dvo/D (D is the intake diameter) was about 0.14, 0.2 and 0.23 for vortices Class C, B and A, respectively.
Hamidi et al. (Sun,) studied this question.