Study on extraction method of liquid jet trajectory in low-speed air crossflow based on image processing
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摘要: 为研究低速横流条件下不同工况液体射流破碎的轨迹特征和影响因素，采用高速摄像仪拍摄射流破碎图像，结合图像处理技术提出针对低速横流情况下液体射流破碎弯曲轨迹的提取方法。该方法首先采用直方图均衡化对灰度化后的原始图像进行增强处理，然后利用最佳直方图熵法（KSW法）及传统遗传算法对图像进行二阈值分割，最后结合Sobel算子和凸包算法对射流轮廓进行检测提取以获得射流轨迹的数据点集。对不同工况下典型射流破碎模式的轨迹提取及非线性拟合结果表明，所提出的方法能够准确提取液体射流轨迹，实现低速横流作用下不同破碎模式的轨迹提取，并且通过非线性拟合得到的射流破碎经验公式可以准确预测射流弯曲轨迹。Abstract: In order to study the trajectory characteristics and influencing factors of liquid jets injected into low-speed air crossflow under different working conditions, the liquid jet breakup image is attained by the high speed camera, and the extraction method of trajectory characteristics of liquid jets injected into air crossflow is proposed, combined with image processing technology. Firstly, histogram equalization is used to enhance the gray-scale original image. Secondly, the optimal histogram entropy method (KSW entropy method) and traditional genetic algorithm are employed to achieve threshold segmentation. Finally, the Sobel operator and convex hull algorithm are served for extracting the jet edge contour, and obtaining the data point set of the jet trajectory. The results of trajectory extraction and fitting of typical jet breakup modes under different working conditions show that the proposed method can effectively extract the characteristics of the liquid jet fracture trajectory, and adapt to the track extraction of different liquid jet breakup modes under the action of low speed air crossflow. Besides, the empirical formula of jet breakup obtained by nonlinear fitting can predict the jet trajectory well.
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湍流作为流体力学的核心分支与前沿课题，其重要性不言而喻。它广泛存在于自然界与工程技术领域，是自然科学与工程技术中尚未攻克的关键难题。自1883年雷诺通过实验揭示湍流以来，尽管历经一个多世纪的研究，湍流的基本机理和规律仍笼罩在神秘之中。湍流不仅与工程技术中的大量问题紧密相连，还涉及众多自然灾害的成因，对国民经济和社会发展具有深远影响。因此，开展湍流研究对于认识自然、解决工程技术难题、推动科技进步具有重大意义。
作为自然界的一种基本现象，湍流的复杂性与跨学科性尤为突出，其展示了随机性与有序性的统一，是无序与有序并存的极端非线性系统，这种特性使得湍流成为物理学领域尚未取得重大突破的基础性课题之一；同时，湍流也与化学、生命科学乃至社会科学等学科现象存在共通之处，在数学上有着共同的描述方法。随着21世纪科学技术的飞速发展，湍流研究迎来了新的机遇与挑战，从经典统计理论到高级数值模拟，从单点测量到空间流场测速，湍流研究手段日益丰富，不断推动我们对湍流本质和机理的深入理解。
为集中展示湍流研究领域的最新进展，促进学科交叉与学术交流，推动研究成果在工程中的应用，《实验流体力学》特别策划了“湍流最新研究进展”专刊。该专刊得到了领域内众多专家学者的积极响应与支持，稿件内容丰富，涵盖了湍流基础理论研究、高级数值模拟、精细化实验测量以及工程应用等多个方面，全面展示了近年来国内湍流研究的新进展与新成果。我们期待本专刊的出版能够进一步激发湍流研究者的热情，促进国内湍流及其应用研究的深入发展，为科学技术进步和国民经济建设贡献新的力量。
“湍流最新研究进展”专刊组稿专家
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图 10 多帧图像的轮廓点提取对比
Fig. 10 Comparison of multi-frame images trajectory point extraction
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图 12 q=41.33、Wej=60.82工况下射流轨迹拟合结果
Fig. 12 Jet penetration fitting result under q=41.33, Wej=60.82
表 1 实验工况
Table 1 Test conditions
实验参数 参数值 液体射流速度uj/(m·s-1) 0~10 液体密度ρj/(kg·m-3) 997 横向气流速度ug/(m·s-1) 5~30 气体密度ρg/(kg·m-3) 1.17 表面张力σ/(N·m-1) 0.0709 液/气动量通量比q=ρjvj2/ρgug2 2~400 射流Reynolds数Rej=ρjvjdj/μj 781~6837 液体Weber数Wej=ρjvj2dj/σ 20~1000 气体Weber数Weg=ρgug2dj/σ 0~20 
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