Experimental and CFD investigations of choked cavitation characteristics of the gap flow in the valve lintel of navigation locks

Abstract

The cavitation is ubiquitous in the water delivery system of high hydraulic head navigation locks. This paper studies the choked cavitation characteristics of the gap flows in the valve lintel of the navigation locks and analyzes the critical self-aeration conditions. The cavitation gap flow in the valve lintel is experimentally and numerically investigated. A visualized 1:1 full-scale slicing model is designed, with a high-speed camera, the details of the cavitation flow is captured without the reduced scale effect. Moreover, the numerical simulations are conducted to reveal the flow structures in the gap. The experimental results show that the flow pattern of the gap flow in the valve lintel could be separated into four models, namely, the incipient (1) the developing, (2), the intensive, (3), and the choked (4) cavitation models. The numerical simulation results are consistent with the experimental data. The choked cavitation conditions are crucial to the gap flow in the valve lintel. When the choked cavitation occurs, the gap is entirely occupied by two cavitation cloud sheets. The gap pressure then decreases sharply to the saturated water vapor pressure at the operating temperature. This water vapor pressure is the ultimate negative pressure in the gap that remains unchanged with the continuous decrease of the downstream pressure. The volumetric flow rate reaches a peak, then remains constant, with the further decrease of the pressure ratio or the cavitation number. At the choking point, the volumetric flow rate is proportional to the root mean square of the difference between the upstream pressure (absolute pressure) and the saturated pressure of the water. Moreover, the pressure ratio is linearly correlated with the downstream cavitation number with a slope of (1 + Ϛc).