Simultaneous planar measurement of droplet velocity and size with gas phase velocities in a spray by combined ILIDS and PIV techniques
Simultaneous planar measurement of droplet velocity and size with gas phase velocities in a spray by combined ILIDS and PIV techniques
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DOI：
10.1007/s00348-009-0802-7
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发表时间：
2010-01
影响因子：
2.4
通讯作者：
Y. Hardalupas;S. Sahu;A. Taylor;K. Zarogoulidis
中科院分区：
文献类型：
--
作者：
Y. Hardalupas;S. Sahu;A. Taylor;K. Zarogoulidis
提出了一种同时测量液滴速度、尺寸和气相速度的新方法，该方法将用于液滴尺寸和速度同时测量的离焦激光干涉成像技术（ILIDS）与用于单个液滴附近气体速度测量的聚焦技术（PIV）相结合。通过去除聚焦液滴图像的眩光点，使用通过ILIDS处理获得的液滴位置，在PIV图像中实现气相播种和液滴之间的区分。当通过ILIDS和PIV技术成像时，两种光学装置的组合可导致液滴中心位置的差异高达约1mm，这可导致PIV图像上液滴的眩光点的错误识别。该差异的大小是CCD阵列上的液滴的图像的位置和散焦的程度的函数，但几乎与液滴的大小无关。具体地，对于ILIDS中的给定散焦设置，它沿着沿着与激光片的传播方向相对应的方向在图像上近似线性地变化。实验发现是支持的理论分析，这是基于几何光学的一个简单的光学配置，复制的光学系统的基本特征。使用单分散液滴发生器测量位置的差异，并从没有“播种”颗粒的多分散喷雾的ILIDS图像中识别的液滴中心中减去。这将PIV和ILIDS液滴中心之间的差异从约1mm减小到约0.1mm，因此增加了在ILIDS图像上找到相应条纹图案和在PIV图像上找到眩光点的概率。总之，它表明，所提出的组合方法可以区分液滴和“播种”颗粒，并能够在多分散喷雾两相测量。
A new approach for simultaneous planar measurement of droplet velocity and size with gas phase velocities is reported, which combines the out-of-focus imaging technique ‘Interferometric Laser Imaging Droplet Sizing’ (ILIDS) for planar simultaneous droplet size and velocity measurements with the in-focus technique ‘Particle Image Velocimetry’ (PIV) for gas velocity measurements in the vicinity of individual droplets. Discrimination between the gas phase seeding and the droplets is achieved in the PIV images by removing the glare points of focused droplet images, using the droplet position obtained through ILIDS processing. Combination of the two optical arrangements can result in a discrepancy in the location of the centre of a droplet, when imaging through ILIDS and PIV techniques, of up to about 1 mm, which may lead to erroneous identification of the glare points from droplets on the PIV images. The magnitude of the discrepancy is a function of position of the droplet’s image on the CCD array and the degree of defocus, but almost independent of droplet size. Specifically, it varies approximately linearly across the image along the direction corresponding to the direction of propagation of the laser sheet for a given defocus setting in ILIDS. The experimental finding is supported by a theoretical analysis, which was based on geometrical optics for a simple optical configuration that replicates the essential features of the optical system. The discrepancy in the location was measured using a monodisperse droplet generator, and this was subtracted from the droplet centres identified in the ILIDS images of a polydisperse spray without ‘seeding’ particles. This reduced the discrepancy between PIV and ILIDS droplet centres from about 1 mm to about 0.1 mm and hence increased the probability of finding the corresponding fringe patterns on the ILIDS image and glare points on the PIV image. In conclusion, it is shown that the proposed combined method can discriminate between droplets and ‘seeding’ particles and is capable of two-phase measurements in polydisperse sprays.