No abstract

Shock waves have undesirable effects, such as excessive dynamic pressure on spillway walls and the extension of flow beyond spillway conduits. To eliminate these detrimental impacts, designers have attempted to detect the characteristics of these waves. Flow interaction with chute piers generates triple waves in the middle walls and sidewalls of spillway conduits. The present study quantitatively investigated the characteristics of these waves with respect to variations in the bottom inclination angle (θ), wall contraction (φ), and Fr numbers (). The results indicated that with the increment of θ, , (φ, ), and (θ, ), the height () and distance () of the first wave increased, which can be helpful for flow aeration. Furthermore, owing to a boost in θ, , (φ, ), and (θ, ), the height of the second wave was decreased. Therefore, the amount of dynamic pressure on the spillway walls was reduced. Moreover, the distance of decreased with a rise in θ, φ and increased with the increment of and (φ, ). As for , raising φ and (φ, ) elevated the height of this wave and declined its distance. An increase in the height of boosted the flow turbulence and aeration.

Geometrical changes and high flow velocity cause flow separation and cavitation in the transition regions of hydraulic structures. A few studies have been conducted on the flow pressure and cavitation index in these regions, and the results need to be still improved. The present study examined the flow pressure and cavitation index variations for expansion angles between 0° and 10° and Froude numbers up to 20.1. Several relevant equations were also suggested to predict permissible angles in the transition regions. The results showed that negative pressure occurred at all lateral expansion angles except 0° when the Froude number was equal to or greater than ≥6.5. The cavitation phenomenon did not occur on the side walls for Froude number up to 4.49. However, the values of the cavitation index were reduced to less than the critical value for the Froude number of 14 when expansion angle was greater than 6°. The results also revealed that the side walls should not be expanded when Froude number was equal to or greater than 17.5. The occurrence of the cavitation on these walls substantially increased for Froude number of 20.1 even as expansion angle equals 0°.