Berrocal Edouard, Kristensson Elias, Richter Mattias, Linne Mark, Aldén Marcus
Department of Combustion Physics, Lund Institute of Technology, Lund, Sweden.
Opt Express. 2008 Oct 27;16(22):17870-81. doi: 10.1364/oe.16.017870.
A novel approach to reduce the multiple light scattering contribution in planar laser images of atomizing sprays is reported. This new technique, named Structured Laser Illumination Planar Imaging (SLIPI), has been demonstrated in the dense region of a hollow-cone water spray generated in ambient air at 50 bars injection pressure. The idea is based on using an incident laser sheet which is spatially modulated along the vertical direction. By properly shifting the spatial phase of the modulation and using post-processing of the successive recorded images, the blurring effects from multiple light scattering can be mitigated. Since hollow-cone sprays have a known inner structure in the central region, the efficiency of the method could be evaluated. We demonstrate, for the case of averaged images, that an unwanted contribution of 44% of the detected light intensity can be removed. The suppression of this diffuse light enables an increase from 55% to 80% in image contrast. Such an improvement allows a more accurate description of the near-field region and of the spray interior. The possibility of extracting instantaneous flow motion is also shown, here, for a dilute flow of water droplets. These results indicate promising applications of the technique to denser two-phase flows such as air-blast atomizer and diesel sprays.
报道了一种减少雾化喷雾平面激光图像中多重光散射影响的新方法。这种名为结构化激光照明平面成像（SLIPI）的新技术，已在50巴喷射压力下在环境空气中产生的空心锥水雾的密集区域得到验证。其原理是利用沿垂直方向进行空间调制的入射激光片。通过适当改变调制的空间相位并对连续记录的图像进行后处理，可以减轻多重光散射带来的模糊效应。由于空心锥喷雾在中心区域具有已知的内部结构，因此可以评估该方法的效率。对于平均图像的情况，我们证明可以去除检测到的光强度中44%的不必要贡献。这种漫射光的抑制使图像对比度从55%提高到80%。这样的改进使得能够更准确地描述近场区域和喷雾内部。这里还展示了提取瞬时流动运动的可能性，针对的是稀水滴流。这些结果表明该技术在诸如空气雾化器和柴油喷雾等更密集的两相流中有广阔的应用前景。
