Experimental study on dam outlet works using a link-sleeve valve with air aspiration

Abstract

In recent years, the importance of hydraulic power generation has further increased because of the movement toward decarbonization and the need to control floods in Japan. For this reason, demand for dam discharge valves has been increasing. However, it is necessary to improve the reliability of valve systems due to their complicated two-phase flows. Therefore, in this study we attempt to apply a link-sleeve valve (LSV), which is usually used for public water supply, as a dam discharge valve. In general, to prevent cavitation erosion, vibration, and noise, air is injected into the downstream pipe of a dam discharge system. Since LSVs are designed to operate in a pressured water supply system, however, the characteristics of air‒water two-phase flows in LSVs have not been investigated. To clarify the characteristics of air entrainment by water jets in an LSV, experiments were conducted using a small-scale LSV model. The results showed that this entrainment is analogous to that which occurs with a jet pump or an ejector at a high water flow rate, while air suction behavior shows complicated characteristics at low water flow rates. This means that air entrainment occurs due to the water jet and that air reverse flow occurs due to the positive pressure gradient in the pipe at a high water flow rate. The present findings could be useful for improving the potential use of LSVs as a lower-maintenance alternative to dedicated dam discharge valves.

Keywords

• valve
• jet flow
• entrainment
• air aspiration
• two-phase flow
• experimental fluid dynamics (efd)