圆柱体并联入水过程空泡演化特性实验研究

运动体并联入水广泛存在于机载射弹灭雷、空投鱼雷饱和攻击等空对海作战方式中,具有极强的工程应用背景.为得到运动体并联入水过程中空泡演化特性,采用基于高速摄像技术的光学测量方法,对圆柱体入水过程开展实验研究.利用图像处理技术对采集的图像序列中的空泡轮廓进行识别提取,通过对比单圆柱体和双圆柱体在不同弗劳德数下的空泡轮廓分析圆柱体并联入水过程的空泡演化特性和弗劳德数对其的影响.实验结果表明:入水空泡整体呈现良好的镜面对称特征,而圆柱体内外侧空泡存在明显的非对称性,当入水时刻的弗劳德数较低时,空泡闭合方式为深闭合,闭合点随弗劳德数增大而后移,当弗劳德数达到临界值时,闭合方式过渡为表面闭合且表面闭合方式下闭合点随弗劳德数增大而前移.在弗劳德数的正激励和环境压力、喷溅回卷负激励作用下,水下不同深度截面上的空泡扩张和空泡中心向外侧偏移量的峰值和时长均随弗劳德数增大呈现先增大后减小趋势,由于不同深度处主导的激励作用不同,故峰值和时长发生转折的弗劳德数临界点不同. 

EXPERIMENTAL STUDY ON CAVITY EVOLUTION CHARACTERISTICS IN THE WATER-ENTRY PROCESS OF PARALLEL CYLINDERS

Water-entry process of parallel moving bodies widely exists in air-to-sea combat modes,such as airborne projectile elimating mines and air-dropped torpedo saturation attack, which has a strong engineering application background. In order to study the cavity evolution characteristics in the water-entry process of parallel cylinders, experimental study on the water-entry process of parallel cylinders is carried out used optical measurement method based on high-speed photography technology. The countor of cavity are identified and extracted with image processing technology. And by comparing the cavity countor between single cylinder and double cylinders with different Froude number at the time of water entry (Fr₀), the cavity evolution characteristics in the water-entry process of parallel cylinders and the effect of Fr₀ are analyzed. The experimental results show that the whole cavity shows good mirror symmetry, while the inside and outside cavity of the cylinder has obvious asymmetry. When the Fr₀ is low, the cavity closure mode is pinch off, and the closure point moves backward with the increase of Fr₀. And when Fr₀ reaches critical value, the closure mode transits to surface closure and the closure point moves forward with the increase of Fr₀ insteadly. Under the positive impact of Fr₀ and the negative impact of ambient pressure and splashing and rolling, the peak value and time length of cavity expansion and outward offset of cavity center at different depth increase first and then decrease with the increase of Fr₀. Due to the different dominant impact at different depths, the critical points of Fr₀ at which the peak and time trends change are different.