Experimental study of anti-cavitation mechanism of valve lintel natural aeration of high head lock

Abstract

To study the serious valve top gap cavitation of Datengxia high head single-lift ship lock, the 1:1 scale slice experiment is carried out, to truly reveal the gap flow characteristics, as well as the valve top gap cavitation characteristics and the anti-cavitation mechanism of natural aeration. Three kinds of cavitation, namely, the throat cavitation, the mainstream inner cavitation, and the valve plate cavitation, are determined and they are found to occur step-by-step in the gap section in the development of the cavitation. According to the anti-cavitation mechanism of the natural aeration, the pressure of the gap flow through the ventilation is increased, to avoid the mainstream inner cavitation and the valve plate cavitation, and to weaken the throat cavitation. The negative pressure zone in the gap section gradually extends with the development of the cavitation until the gap section is filled with a stable −10 m water head. When the natural aeration measure is employed, the pressure in the gap section approximately reaches the −2 m water head, and the cavitation disappears. The systematic tests reveal the quadratic polynomial relationship between the pressure in the gap and the ventilation per meter width. The pressure, which corresponds to the maximum value of the ventilation at the beginning of the gap, approximately reaches the −2 m water head, and the pressure and the ventilation reach the equilibrium state limit. When the pressure in the gap increases when the valve is opened, the ventilation gradually decreases until the natural aeration stops. The gap section length for the high head valves has a great effect on the natural aeration and should be long enough to maintain the stable negative pressure in the gap, whereas the throat width has a minimal effect. Results can be used for the anti-cavitation design of the high head lock valve.