Hydraulic Model Studies for the Penstocks for Grand Coulee Third Powerplant,

摘要

Hydraulic model investigations were performed on a 1:41.75scale model to aid in the design of the penstock entrances and lower bends of the Third Powerplant at Grand Coulee Dam. The initial entrance with a 2:1height-to-width ratio,entrance area equal to penstock area,and a small radius entrance curve indicated excessive head loss and poor pressure distribution along the flow surfaces. A longer compound radius entrance curve reduced the head loss and improved the pressure distribution along the flow surfaces. A more economical entrance with a 1-1/2:1height-to-width ratio and the compound radius entrance curve showed excellent hydraulic characteristics and was selected for prototype installation. The proposed trashrack will add to the head loss but will not affect other flow conditions. A model with flared entrance curves on the left side and roof was also tested but showed no significant improvements in flow characteristics. A model with the entrance area equal to 9/10the penstock area indicated excessive head loss and poor pressure conditions. Vortex observations indicated the possibility of air-entraining vortices with all entrances tested. More detailed vortex studies on another model will be reported separately. Three types of lower bends were investigated. None showed any particular hydraulic advantage.