A Study on Ultra-Highspeed Micro-Flow

为了弄清超高速微流的流动特性和动力学特性，我们对超高速微流的空化特性进行了研究。在此基础上，系统地观察了喷嘴内和喷嘴出口附近的流态，以及狭窄水道中的空化射流，并对空化流动进行了数值模拟。主要研究结果如下：1.对超纯水进行了测试，其电阻率大于18MOMEGA/cm。而且，我们明确指出，水的相对含气率比自来水和静止水的相对含气率高得多，这是空化形成和发展的重要因素。为了避免对超纯水的污染，我们用一种特殊的滤膜对超纯水中的空气进行脱气处理，得到了相对含气率小于0.2.2的特殊超纯水。为了弄清楚Flow…系统地研究了多种超高速流型，对空气中和水中的超高速水射流进行了观测和冲蚀试验。对于水中的射流，结果表明，射流是周期性地脱离空化气泡云。同时，冲蚀强度与空化气泡云密切相关。系统地研究了淹没高速水射流周围空化引起的冲蚀特性，发现淹没水射流对清洗和喷丸是非常有用的。由于在水下水射流情况下，气泡破裂时的空化脉冲压力可以有效地用于清洗和强化。并给出了几种喷嘴的合适喷射条件。为了弄清狭窄水道中的超高速流态，利用最大取景速率为40500帧/秒的高速摄像机和数字图像处理技术，对狭窄水道中的空化射流进行了仔细的观测。狭窄水道中的空化气泡云与上述与严重侵蚀空化相关的空化云一样周期性地脱落。较少

In order to make clear the flow characteristics and the dynamics in the ultra-highspeed micro-flow, we examined the cavitation characteristics of the ultra-highspeed flow. Then, we systematically observed the flow pattern in the nozzle and near the nozzle-outlet as well as the cavitating jet in a narrow watercourse, and also tried to simulate the cavitating flow numerically. The obtained results are summarized as follows :1. We tested the ultra-pure water, whose resistance rate is more than 18 MOMEGA/cm. And, we made clear that the relative air content rates of the water, which is an important factor on the cavitation inception and develops, are considerably higher than that of tap-and still water. Then we made a special facility to degas the air within the ultra-pure water by using a special filtering membrane in order to avoid polluting the ultra-pure water, and we got the special ultra-pure water, whose relative air content rates are less than 0.2.2. In order to make clear the flow … More pattern of ultra highspeed flow systematically, we carried out the observation and the erosion test on ultra highspeed water jets in the air and in the water. In the case of the jets in the water, it is shown that the jets are periodically shedding the cavitation bubble clouds. And also the erosion intensity is closely related to the cavitation bubble clouds.3. The above-mentioned the erosion characteristics induced by the cavitation around the submerged highspeed water jets are systematically examined, the submerged water jets are very useful for cleaning and peening. Since the cavitation-impulse-pressures at the bubble collapsing can be effectively used on the cleaning and the peening, in the case of the submerged water jets. And also the suitable injection condition is shown for several nozzles.4. In order to clarify the ultra highspeed flow pattern in a narrow watercourse, the cavitating jet in a narrow watercourse is carefully observed by means of a highspeed video camera, whose maximum framing rate is 40,500 frames per second and a digital image processing technique. The cavitation bubble clouds in the narrow watercourse are periodically shedding as same as the above-mentioned cavitation clouds associated with severely erosive cavitation. Less