Velocity and pressure field in skimming flow in stepped spillways

In stepped spillways the presence of steps enhance the flow turbulence and hence the growth of the boundary layer. The earlier inception of air entrainment in this type of hydraulic structures, compared with a smooth spillway is considered an advantage in terms of cavitation risk. Nevertheless the point of inception is also a function of the discharge, increasing the non aerated zone for higher flow rates. The existence of sufficient air content next to the solid boundaries prevents cavitation damage, the region upstream and next to the inception point will be then critical for evaluation of cavitation risk. In this work, velocity and pressure field in the non aerated region of the spillway were measured. For the velocity field it is used the Particle Image Velocimetry (P.I.V.) technique, this non intrusive measurement can bring some insight about the internal flow features that fill the cavities between the main flow and the faces of the steps