水射流简答题

空化射流一．概念和描述1）Only happened in fluid. On any occasion, it will never appear in air or solid2). Cavitation results from the local pressure decreasing in fluid. Therefore, it can be controlled through adjusting the degree of pressure decrease.3).Cavitation relates to the cavity’s initiation and disappear;4 ) . Cavitation is a dynamic phenomenon in which cavity(bubble) initiates, grows and collapse;5). No matter the fluid’s states, stationary or flow, it is possible to appe ar cavitation;6). Cavitation can occur not only inside the fluid, but at the interface of solid and fluid. 1）。

在任何场合，它永远不会出现在空气或固体仅发生在流体。

2）。

局部压力降低流体的气蚀的结果。

因此，它可以进行控制，通过调整压力下降的程度。

3）。

气蚀腔的萌生和消失;4）。

气蚀是一种动态现象腔（气泡）启动，成长和崩溃;5）。

不管流体的状态，静止或流动，有可能出现气穴现象;6）。

空现象不仅内部的流体，但在固体和流体的界面。

二．Clarification澄清1.Traveling cavitation 旅行气蚀Single transient bubble in liquid forms, grows, and collapses.This transient traveling bubble may appear at the low- pressure area along the solid surface, or at the core of moving vortex or high turbulent area of shearing field.单瞬态泡在液体的形式，成长，并且崩溃。

这短暂的泡沫可能出现的低压区沿固体表面，或在移动涡或高湍流剪切场面积的核心。

2.Fixed cavitation固定气蚀Bubble or cavity, at stable state, fixes on the solid surface.Because of the fluid mixture or fluid back-flow at the end section of cavitation area, fixed bubble may grow and collapse.Strong oscillation will appear.泡泡或空腔，在稳定的状态，固定在固体表面上。

由于流体混合物或液体回流的气蚀区的端部，固定的气泡生长和收缩。

强会出现振荡。

3.Vortex cavitation涡气蚀One of the earliest cavitation able to be observed by people.It always appears at the tips of ship’s propellers and sometimes is called “tip cavitation”. Only when the bubble of this cavitation collapses at or near the solid surface, can strong cavitation erosion happen.一个能够被人们所观察到的最早的汽蚀。

它总是出现在船舶螺旋桨的提示，有时被称为“尖气蚀”。

只有当气泡的气穴固体表面或接近崩溃，发生强烈气蚀侵蚀。

4.Vibratory cavitation 振动气蚀Above, common feature: a fluid unit passes the cavitating area only one timeVibratory cavitation: continuous big-amplitude and high-frequency pressure vibration.A fluid unit will undergo cavitation- recycle for many times以上，共同特点是：流体单元通过空泡面积只有一次振动气蚀：连续大振幅和压力高频振动。

一种流体单元将进行多次循环气蚀三．Cavitation erosion空蚀Heterogeneous mixture of vapor and gas pockets or “voids,” frequently causes a rapid erosion of adjacent material structureA very incomplete understanding of the mechanisms by which a “ cavitation field” causes rapid damage to adjacent solid material异构混合物的蒸汽和气体的口袋或“空洞”，经常会导致迅速侵蚀相邻材料的结构一个非常不完整的理解“气穴场”的机制，导致迅速伤害到相邻的固体材料Mechanisms of Cavitation Damage空蚀破坏的机制1.Micro-jet’s Action微射流的行动Cavitation holds the promise of a new and exciting way to fabricate both top down and bottom up nanostructures. Cavitation bubbles are created when a liquid boils under less than atmospheric pressure.气蚀持有一个新的和令人兴奋的方式来制作纳米结构自上而下和自下而上的承诺。

空化气泡时创建低于大气压力下液体沸腾。

The collapse process occurs supersonically and generates a host of physical and chemical phenomena. The collapse of a cavitation bubble near an object occurs asymmetrically and launches a reentrant microjet directly towards it.超音速发生倒塌过程，并产生一系列的物理和化学现象。

不对称的物体附近发生空化泡的崩溃和启动折返微喷，直接朝它。

If permanent air in the bubble, at the final stage of bubble collapse, the temperature will rise rapidly to a high level. As the collapsing duration is very short, the heat exchange is impossible to happen with the ambient fluid. When the super-hot air contacts with the metal surface, it will be heated to melting point如果永久空气中的泡沫，泡沫崩溃的最后阶段，温度将迅速上升到一个较高的水平。

由于折叠的持续时间很短，该热交换是不可能发生的，与环境流体。

超热空气与金属表面接触时，它会被加热到熔点。

四。

Cavitation Inception and Parameter Effects 空泡起始和参数影响The cavitation inception means that at or near the place of lowest pressure, there appears micro-cavity(bubble)空化起始装置，压力最低处或附近的地方，出现微腔（气泡）1.parameters effect参数效果1）.Effects of Fluid Parameters流体参数的影响(1) temperature温度；(2) pressure 压力；(3) other parameters其他参数2）gas content气体含量gas content , the number of bubble and the extent of the cavitating region, but the collapse voilence of individual bubble 个别气泡的气体含量，气泡的数量和程度的空泡地区，但坍塌VOILENCE的3）cavitation number空化数If cavitation number is increased , the number and mean diameter of bubbles , collapsing pressure differential and collapse violence。

If the cavitation number is increased in a given situation by reducing the velocity and maintaining constant pressure, the damage will probably be decreased.如果空化数增加时，气泡的数量和平均直径，崩压力差和崩溃暴力。

如果在一个给定的情况下，通过减少的速度和保持恒定的压力，空化数增加的损害可能会下降。

2.Cavitation Bubble Dynamics空泡动力学High-speed photography and acoustic measurements. 高速摄影和/声学测量。

1)Two characteristic effects:两个特征的影响：the emission of shock waves upon the collapse of the bubble泡沫崩溃后排放的冲击波The generation of a high-speed liquid jet directed towards the (solid) boundary 一种高速液体喷射的产生朝向（固体）的边界2)Rayleigh analysis瑞利分析(1）Cavitation damage is primarily a result of fluid-mechanical rather than corrosive effects气蚀破坏主要是流体机械的结果，而不是腐蚀作用(2）The analysis shows the potential for the generation of very high fluid pressure and velocities by cavitation bubble collapse该分析显示了非常高的流体压力和速度的产生空化泡崩溃的潜在的(3）The energy would become infinite at the completion of bubble collapse, when the originally finite bubble has become a mathematical point. Infinite energy is then ascribed to zero mass, so that no violation of the energy-conservation law is involved .能量将变得无限大的气泡破裂完成后，原来有限的气泡时，已成为数学的角度。