Glover A R, Skippon S M, Boyle R D
Appl Opt. 1995 Dec 20;34(36):8409-21. doi: 10.1364/AO.34.008409.
A full-field, time-resolved interferometric method for the characterization of sparse, polydisperse spray systems is reported. The method makes use of the angular intensity oscillations in the wide-angle forward-scatter region. A pulsed laser is used to illuminate a planar sheet through the spray, which is imaged, out of focus, from the 45°direction. The image consists of a set of out-of-focus spots, each of which represents an individual droplet, and superimposed on which is a set of fringes corresponding to the angular intensity oscillations of that droplet. Macrophotographic recording with high-resolution digitization for image analysis provides a full-field capability. The spatial frequency of fringes on each spot in the image plane is dependent on the diameter of the corresponding droplet in the object plane, and a simple geometric analysis is shown to be appropriate for the calculation of the spatial frequency of fringes as a function of droplet size. Images are analyzed automatically by a software suite that uses Gaussian blur, Canny edge detection, and Hough transforms to locate individual droplets in the image field. Fringe spatial frequency is then determined by least-squares fitting to a Chirp function. The method is applicable to droplets with diameters in the range of several millimeters to several hundred millimeters and number densities of up to 10(3) to 10(4). The accuracy of the method for droplet-size determination has been evaluated by measurements of monodisperse aerosols of known droplet size, and measurements of droplet-size distribution in a polydisperse aerosol produced by a gasoline fuel injector are also presented. An extension of the method, using high-speed photography to measure two components of velocity in addition to size and position, is discussed. A two-wavelength approach may also offer the capability to measure the concentration of model fuel additives in droplets, and the results of a feasibility study are described.
报道了一种用于表征稀疏、多分散喷雾系统的全场、时间分辨干涉测量方法。该方法利用广角前向散射区域中的角强度振荡。使用脉冲激光通过喷雾照亮一个平面薄片，从45°方向对其进行离焦成像。图像由一组离焦斑点组成，每个斑点代表一个单独的液滴，并且在其上叠加有一组与该液滴的角强度振荡相对应的条纹。通过高分辨率数字化进行宏观摄影记录以进行图像分析，提供了全场测量能力。图像平面中每个斑点上条纹的空间频率取决于物平面中相应液滴的直径，并且显示出一种简单的几何分析适用于计算作为液滴尺寸函数的条纹空间频率。通过使用高斯模糊、Canny边缘检测和霍夫变换的软件套件自动分析图像，以在图像场中定位单个液滴。然后通过对Chirp函数进行最小二乘拟合来确定条纹空间频率。该方法适用于直径范围从几毫米到几百毫米、数量密度高达10³至10⁴的液滴。通过对已知液滴尺寸的单分散气溶胶进行测量，评估了该方法确定液滴尺寸的准确性，并且还展示了对汽油燃料喷射器产生的多分散气溶胶中液滴尺寸分布的测量。讨论了该方法的扩展，即使用高速摄影来测量除尺寸和位置之外的速度的两个分量。双波长方法也可能提供测量液滴中模型燃料添加剂浓度的能力，并描述了可行性研究的结果。
