Cavitation erosion by single laser-produced bubbles
Cavitation erosion by single laser-produced bubbles
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DOI：
10.1017/s0022112098008738
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发表时间：
1998-04-25
影响因子：
3.7
通讯作者：
Lauterborn, W
中科院分区：
文献类型：
--
作者：
Philipp, A;Lauterborn, W
为了阐明空化侵蚀的机理，详细研究了激光在水中产生的单个空化气泡的动力学以及由此引起的平板金属试件的表面损伤。用高达100万帧/S的高速摄影记录了气泡动力学的特征效应，特别是高速液体射流的形成和崩溃时刻的冲击波发射。当气泡在距离固体边界(Gamma=2，其中Gamma=2，其中Gamma=S/R-max，S是形成时刻的边界到气泡中心的距离，R-max是气泡的最大半径)的距离小于其最大半径的两倍处产生时，可以观察到损伤。只有在较小的初始距离(伽马小于或等于0.7)时，喷流的撞击才会造成损害。在该地区，撞击速度上升到83m S(-1)，对应的水锤压力约为0.1 Gpa，而在Gamma>；1，撞击速度小于25m S(-1)。最大的侵蚀力是由与边界直接接触的气泡破裂引起的，压力高达几个Gpa作用在材料表面。因此，气泡在崩塌阶段由于BJerkines力加速朝向边界的破坏效果是至关重要的。气泡在第二次坍塌时接触边界，在第一次坍塌时触及边界。在坍塌气泡的接触位置发现铝试件上的凹痕。在伽马=1.7到2的范围内，气泡主要向下坍塌到一个点，观察到气泡中心下方的一个坑。当伽马小于或等于1.7时，由于喷流通过气泡中心，气泡形状变为环形。与这个气泡环衰变成多个微小气泡的情况相对应，每个气泡都沿着环面的圆周分别坍塌，所观察到的损伤也是圆形的。Gamma小于或等于0.3且Gamma=1.2到1.4范围内的气泡造成的损害最大。发现损伤区域的总直径与最大气泡半径成比例关系。由于可能产生数千个几乎相同的气泡，即使是硬钢试件也可以测试其抗气蚀性能。
In order to elucidate the mechanism of cavitation erosion, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail. The characteristic effects of bubble dynamics, in particular the formation of a high-speed liquid jet and the emission of shock waves at the moment of collapse are recorded with high-speed photography with framing rates of up to one million frames/s. Damage is observed when the bubble is generated at a distance less than twice its maximum radius from a solid boundary (gamma = 2, where gamma = s/R-max, s is the distance between the boundary and the bubble centre at the moment of formation and R-max is the maximum bubble radius). The impact of the jet contributes to the damage only at small initial distances (gamma less than or equal to 0.7). In this region, the impact velocity rises to 83 m s(-1), corresponding to a water hammer pressure of about 0.1 GPa, whereas at gamma > 1, the impact velocity is smaller than 25 m s(-1). The largest erosive force is caused by the collapse of a bubble in direct contact with the boundary, where pressures of up to several GPa act on the material surface. Therefore, it is essential for the damaging effect that bubbles are accelerated towards the boundary during the collapse phases due to Bjerknes forces. The bubble touches the boundary at the moment of second collapse when gamma < 2 and at the moment of first collapse when gamma < 1. Indentations on an aluminium specimen are found at the contact locations of the collapsing bubble. In the range gamma = 1.7 to 2, where the bubble collapses mainly down to a single point, one pit below the bubble centre is observed. At gamma less than or equal to 1.7, the bubble shape has become toroidal, induced by the jet flow through the bubble centre. Corresponding to the decay of this bubble torus into multiple tiny bubbles each collapsing separately along the circumference of the torus, the observed damage is circular as well. Bubbles in the ranges gamma less than or equal to 0.3 and gamma = 1.2 to 1.4 caused the greatest damage. The overall diameter of the damaged area is found to scale with the maximum bubble radius. Owing to the possibility of generating thousands of nearly identical bubbles, the cavitation resistance of even hard steel specimens can be tested.