航行体云状空泡稳定性通气控制

Gas control on the ventilated cavitation stability around an underwater vehicle

摘要:

为研究水下航行体云状空泡稳定性, 通过水洞实验对水下航行体模型云状空泡进行了实验研究, 对比分析了不同空化数对水下航行体通气空泡稳定性的影响, 分别分析了不同空化数下通气空泡发展、断裂和脱落等准周期性波动特性以及脱落速度和空泡发展对表面压力的影响, 得到了通气对流动控制效果和局部不稳定性机理.结果表明：在通气作用下空泡内的透明部分逐渐增大, 在逆压梯度的作用下, 回射流形成并向航行体前部运动, 空泡前部由透明逐渐变为浑浊, 当回射流到达空泡前段, 空泡表面出现波动, 在回射流的作用下空泡以涡团形式发生脱落, 航行体模型肩部通气空泡的发展和脱落随着空化数的控制而呈现明显的不同；当空化数较大时, 空泡发生断裂、脱落两个过程；当通气量增大空化数减小后, 空泡呈现断裂、融合、脱落3个过程, 此时空泡呈现稳定发展的特性；空泡平均脱落速度随着空化数的减小而减小；实验结果也表明了不同时刻航行体表面压力脉动情况, 空泡闭合位置存在压力峰值, 航行体表面压力随着空泡的脱落出现波动

Abstract:

The objective of this paper is to investigate the cavity stability around an under-water vehicle in the water flow. The water tunnel experiment for the cavity around the vehicle was investigated. The experiment was carried out to study cavity developing, break-off and shedding with different cavitation number. The experiment also studied the velocity of shedding cavity and the pressure of the vehicle surface. The mechanism of gas control and cavitation stability was obtained. The results show that the transparent cavity increases gradually with ventilation. Re-entrant jet appears and moves back to the front of the vehicle under adverse pressure gradient at the closure of the cavity. The transparent cavity in front of it is replaced by opaque one gradually at the same time. The shedding cavity rolls up and large cavity vortexes sheds toward downstream. When the re-entrant jet arrives at the forepart of the vehicle, the cavity boundaries become wavy. The characteristics of cavity developing and shedding vary as cavitation number is changed. When the cavitation number is bigger, it is found that the shedding generally contains two processes: cavity break-off and cavity shedding. With the decrease in the cavitation number, the shedding contains three processes: cavity break-off, conjunction and cavity shedding. The average shedding speeds decrease with the decreasing of the cavitation number. The experimental results also show that the pressure signals at different instants destabilize on the vehicle surface; fluctuant pressure peak is detected at the closure region of the cavity. Surface pressure fluctuations occur on the vehicle surface with the cavity shedding