重力场对轴对称体稳定空泡形态影响的实验研究

Experimental Study of the Influence of Gravity Field on the Shapes of Axially Symmetric Steady Cavity

水下超空泡航行器的空泡几何形状对航行器的受力状态与航行性能关系重大 ,在水洞模型超空泡实验中发现重力场是影响空泡几何形状的主要原因之一 ,该问题此前虽有文献提及 ,但未见有具体阐述 ,为此专门开展了在不同佛汝德数下对不同头型的轴对称体模型空泡几何特性的实验研究。实验中获得了大量变形空泡的录像 ,并对空泡的外形进行了定量处理 ,对实验结果进行了定性与定量分析 ,获得了重力场对轴对称体空泡几何形状影响的规律性结果 ,同时对重力场影响空泡形变的机理作了探讨分析。

With the application of supercavitation to viscous drag reduction of underwater vehicles, the research on cavity shape becomes an important field. We studied the influence of gravity field on cavity shape in this paper, which is seldom studied in the past several years. The influence of gravity causes essential deformation of the artificial cavity shape so that it completely determines the cavity closure character and the gas leakage from the cavity. Our main purpose is to determine under what conditions the influence of gravity must be considered, and under what conditions the influence of gravity can be ignored. Owing to difficulty of theoretical analysis, we tried to solve the problem by means of experimental investigation. We carried out water tunnel experiments on axially symmetric model for different Froude numbers and got a mass of kinescope of transformative cavity. In order to measure transformative cavity, we presented an image manipulation method that can not only remove the refractive error induced by different media, but also can get the quantitative results of images. The results of data processing for different headforms, cavity numbers and Froude numbers show that gravity field is a primary factor for influencing cavity shapes. We draw the following four conclusions: (1) The quantitative processing of cavity shapes is feasible. (2) Cavity transforms in “S” mode, and transformation in aft-cavity is more serious than that in fore-cavity. (3) When Froude number (F r) times cavity number (σ) is greater than 1, the influence of gravity field on cavity shapes can be ignored. (4) The above 3 conclusions apply to different headforms.