光流法在掺气水流流场测量中的应用进展

Advances and challenges to optical flow applications in measurement of highly aerated flow field

水利设施中掺气水流运动速度估计一直是水气两相流领域重点研究的课题,由于掺气水流中气泡复杂的演变机制和剧烈的湍动瞬变,导致现有的测量技术难以准确的表征水流流场情况。基于光流法的流场可视化技术因其独特的优势而成为图像识别领域重点研究的方向。光流法能够根据像素亮度计算出细观气泡运动的高分辨率光流场,弥补了传统的基于粒子图像测速技术的不足。为了全面反映国内外研究人员应用光流技术对掺气水流流场可视化估计的进展,本文从经典光流法的原理出发,综述了目前用于掺气水流中的几种光流技术及其特点,然后总结了光流技术在处理掺气水流这种复杂场景时采用的关键技术和参数选择情况。最后,探讨了光流技术在掺气水流应用中所面临的挑战和前沿问题,并对其未来的发展做出展望。

Velocity measurement of highly aerated flows is a key issue in air-water two-phase flow research and hydraulic engineering.Bubbly flows,self-aerated or artificially-aerated,are very complicated in evolution mechanism and rapid turbulent fluctuations;currently-used techniques are limited in accurate measurements of their flow velocity and turbulences.Optical flow-based flow visualization technologies attract a great interest in the field of image recognition due to its unique advantages.The optical flow method enables calculation of the high-resolution optical fields for the meso-scale movement of air bubbles by using the brightness of pixels on the image,thereby making up for the shortcomings of traditional particle image velocimetry.This paper discusses the principle of classical optical flow methods and reviews the existing optical flow technologies applicable to highly aerated flows,so as to provide a comprehensive picture of the advances and the state of the art in the aerated flow visualization applications of these technologies.Then,we sum up the key processing techniques and parameter selections for applications to the complicated cases of highly aerated flows.Finally,the challenges and frontiers of related theoretical and practical issues faced in highly aerated flow measurements are discussed,and their future development directions are prospected.