论船闸输水反弧阀门廊道减蚀防振措施——Ⅱ.空化成因与流态振荡机理探讨

On the Design of Reverse Tainter Gate Tunnel of a Shiplock Against Cavitation and Vibration Ⅱ. An Analysis on the Hydrodynamic Mechanism of Flow Cavitation and Oscillation

输水反弧阀门廊道的空蚀、门振与声震,是高水头船闸设计需要解决的关键技术问题。本文第1部分分析了急变分离流现象的特点、总结了工程问题与研究设计现状。在本部分,结合对近几年研究成果的总结,分析了水流空化成因与流态振荡机理,为探讨合理的减蚀防振措施提供理论依据。文中分析了旋涡空化、门楣缝隙空化、阀门底缘空化与粗糙壁面空化的特点与成因,强调在设计中应特别重视可能的旋涡型空化,认为小开度的水流振荡属于低频拍动现象,其Strouhal数小于0.025,而大开度发生的旋涡合并与分裂脱落是诱发剧烈流态振荡的根源,其Strouhal数为0.2左右。为探明阀门廊道内复杂的急变分离流现象,应当结合数值计算、模型试验与原型观测方法继续深入研究。

In the reverse-tainter-gate-tunnel design of a high-rise shiplock water-filling system, it is of crucial importance to prevent flow cavitation and gate vibration. In part (Ⅰ) of this paper a review was given for the flow phenomena and the existing engineering problems. With the efforts to provide a theoretical basis for engineering design, this part makes an analysis on the hydrodynamic causes of flow cavitation and oscillation in the gate tunnel, most of which is primarily based on the research work completed in recent years. Flow cavitation is classified as four major types, vortex cavitation, gate-lintel cavitation, gate-bottom-edge cavitation as well as rough-surface cavitation. The possible cavitaion damage and hydrodynamic cause are described for each type of cavitation, emphasizing that special attention should be paid to the harmful vortex cavitation. By the analysis, it is shown that the flow oscillation at gate-opening less than 45% is caused by the flapping motion of the shear layer at the bottom tunnel wall and is characterized by a Strouhal number less than 0.025; while the strong flow oscillation at gate-opening greater than 45 % is caused by the merging, splitting and shedding process of well-organized large eddies, with a Strouhal number around 0.2. It is suggested that further efforts in combining the methods of scale-model experiment, numerical simulation study and prototype test, should be made to fully understand the complicated unsteady separated flow phenomena.