绕水翼空化非定常的动力特性

Unsteady Dynamics of Cavitating Flows around a Hydrofoil

采用试验的方法研究绕水翼空化流动的非定常流体动力特性。试验在一闭式空化水洞针对一Clark-y型水翼进行。采用高速摄像技术观测不同空化阶段的空穴形态;应用自开发软件分析空穴形态随时间的变化;测量翼型所受的升阻力和升力方向的加速度;对上述的数据进行频谱分析。试验结果表明,绕水翼空化流动中,空穴形态及其对应的动力特性随时间的变化过程存在两种不同的模式。当4<σ/2α<6时,空穴平均相对长度为l/c<0.7,由空穴形态和升力系数得到的功率谱峰值对应的斯特劳哈尔数大于0.3;当σ/2α<4,空穴平均相对长度为0.7<l/c<1.0,绕水翼空化流动呈现明显的非定常性,翼型吸力面出现了大量空泡团周期性的脱落,升力系数功率谱峰值对应的斯特劳哈尔数在0.18左右,空泡团脱落频率不随空化数的变化而改变。

To address the dynamic characteristics of cavitating flows,the unsteady characteristics of cavitating flows around a Clark-y hydrofoil are investigated experimentally.The experiments are carried out in a rectangular test section of a closed cavitation tunnel.A high-speed video camera is used to visualize the unsteady cavitating flow patterns.The observition results are analysed by using a home-developed software.The drag and lift under different cavitation conditions are measured.The spectral analysis of the measured date is conducted.It is found that the dynamic characteristic of the cavitation varies considerably with the changes of the cavitation number.Two stages of the development of unsteady cavitation are observed.When 6 〉σ /2α〉 4,the average non-dimensional length of the cavities is less than 0.7,while the Strouhal number,based on chord length,corresponding to the peak of the power spectral densities of the cavity length and lift,is above 0.3.When σ /2α 〈4,the non-dimensional cavity length is in the range of 0.7〈 l^- /c〈 1.0.A low frequency shedding of cloud cavitation results in a strong oscillation in lift at the Strouhal number of about 0.18.This frequency is relatively insensitive to changes in cavitation number.