绕平头回转体非定常空化流体动力特性研究

采用高速全流场显示技术和动态应变式测力系统实验研究了绕平头回转体的非定常空化流动及其动力特性。实验在闭式水洞中进行,采用高速摄影的方法观察了在不同空化数下绕平头回转体的空穴形态,应用自编软件对图像进行处理获得了空穴尺度随时间的变化,测量了所受到阻力,并对空穴尺度和阻力信号的时域与频域进行了分析,得到了平头回转体阻力在非定常空化阶段的时频特征。结果表明：在各个空化阶段,空穴尺度及其对应的动力特征均呈现明显的非定常特性。在空化数较大时（σ=1.05～1.20）,仅在回转体头部后端区域存在不稳定的空泡脉动区域,此时,由阻力系数得到的时频信号呈无规则的波动;当空化数降至0.75以下时,出现了大尺度空穴断裂与空泡团脱落现象,捕捉到了绕平头回转体空泡的非定常周期性脱落过程和典型特征频率。绕回转体阻力系数曲线随着空化数的减小波动幅度不断加大,并且空穴尺度和平头回转体所受阻力主频随之发生改变,特征频率逐渐显现,并且形态特征频率与动力特征频率存在高度的相关性。

Study on the unsteady cavitating flow dynamic characteristics around a 0-caliber ogive revolution body

The unsteady characteristics of cavitating flows around a 0-caliber ogive revolution body are investigated by experimental methods.Experiments are carried out in a rectangular test section of a cavitation tunnel.A high-speed video camera and dynamics force measurement system are used to observe the unsteady cavitating flow patterns and the resistance of the 0-caliber ogive revolution body,under different cavitation conditions.The cavity size and resistance data are analyzed in time and frequency domain.The time-frequency characteristics of unsteady cavitating flows around the 0-caliber ogive revolution body are obtained.The results show that the cavity development and corresponding dynamic characteristics has obviously changed under different cavitation numbers.When the cavitation number is 1.20~1.05,the unstable cavitation oscillation region can be only observed in the back of body head,and the resistance coefficient of fluctuates irregularly with time.When the cavitation number is decreased to below 0.75,a periodic shedding process can be observed and the typical characteristics of frequency are captured.The fluctuations of the resistance coefficient increase with the decrease of cavitation numbers.