Design of Aerator for a Rectangular,Bottom Outlet by Physical Model

In high speed flows, such as flow in bottom outlets any change in the flow boundary may result in high negative pressures and cavitation attack. In the present work, the bottom outlet of a large buttress dam was studied in a physical model. This bottom outlet had a rectangular section and was damaged by cavitation attack every year after operation. By conducting many experiments, it was revealed that a very mild expansion along the right wall was the reason for high negative pressures and cavitation attack. Installation of an aeration system right upstream of the expansion was proposed for elimination of cavitation damage. Aeration system included a ramp on the conduit bed and right wall. Since the right wall tended away from the flow along the mild expansion, enough space for aeration was provided for the wall ramp. Results of experiments showed that a completely aerated jet formed on the conduit aerator. Moreover measurements showed that owing to aeration, negative pressures downstream of the wall expansion were decreased to an acceptable level. The results of present work are useful in cavitation studies and also design of aerators in bottom outlets.