紊流相干结构对推移质运动特性影响研究

The sediment movement is the result of the interaction between turbulence and sediment particles, and the turbulent coherent structures will have an effect on the sediment motion. The unsteady characteristics of turbulent coherent structures and sediment motion are obvious, and due to the limited observation and analysis, the understanding of the sediment motion mechanism of turbulence structure and sediment is still not clear. In present project, the particle image velocity (PIV) measurement system was employed to recognize the characteristics of streaky structure and spanwise vortexes, to analyze the coherent structures in turbulence flow. On the basis of this, the experiments of sediment transport were carried out. The measurements involve tracing the streaks with both natural sparse sand and bedload sediment，recording the streak images by a high-resolution camera，and extracting geometrical features of the steaks through mathematical morphology procedure. The target is to study the interaction mechanism of turbulent coherent structure and sediment particle movement. Finally, the shape of the sand ridge of the bed surface was obtained through the binocular recognition system. Compared with the high or low probability region of sediment transport obtained by the high speed camera technology, we can further study the causes of the surface morphology of bedload movement. Research results could be used to improve the bedload sediment transport forecasting and the turbulent coherent structure model， to provide theoretical and experimental basis, has important scientific significance and practical value. The research results provide theoretical and experimental basis for studying the effect of turbulent coherent structure on the movement of mottled masses, which is of great scientific significance and practical value.

推移质运动是紊流与泥沙相互作用的结果，紊流相干结构的存在将对推移质运动产生影响。紊流相干结构和泥沙运动非稳态特征明显，加之观测手段和分析受限，现阶段对紊流结构与泥沙作用机理的理解还不够深入，影响对推移质输沙的预测及水沙相互作用机理的认识。本项目首先通过粒子图像测速(PIV)系统，实现对紊流相干结构中的条带结构和横向涡结构的识别，分析紊流相干结构特征。在此基础上，开展推移质输沙运动试验，通过图像处理技术和形态学方法，识别稀疏沙条带结构和推移质运动概率高低的条带结构，计算上述条带结构的特征尺度，建立紊流相干结构与泥沙颗粒运动的相互作用机理。最后，通过双目识别系统获取床面沙脊沙垄形态，与高速摄像技术所获取的推移质运动概率高低区域进行对比，更深入的研究推移质运动床面形态形成的原因。研究成果为研究紊流相干结构对推移质运动影响提供理论和试验依据，具有重要科学意义和实用价值。

推移质运动与河流演变、水利工程的设计、建设和运行紧密相关。紊流中广泛存在的相干结构将与泥沙和床面相互作用，但运动机制尚不明确，对此过程开展精确量化分析，对泥沙理论和工程应用具有重要意义。本项目旨在结合流体力学和河流动力学两大学科体系，发展新的测量技术和智能化分析方法，提高对水沙运动研究的时空分辨率。首先开展明渠紊流PIV试验测量紊流xz、xy面二维流场，通过定量分析条带结构特征尺度和POD方法提取的流场能态特征，研究紊流相干结构模型及其维持机理；第二，通过图像处理、PTV算法和卡尔曼滤波方法，在颗粒尺度上定量分析推移质运动区域、速度和轨迹特征；第三，基于SFM方法对冲刷后床面地形进行三维重构。最终将推移质运动过程中紊流相干结构、推移质颗粒运动规律和床面结构形态三者进行耦合，建立统一的紊流相干结构和推移质运动相互作用机制。本项目研究成果可为泥沙运动理论研究、宏观水沙调控及预测提供科学支撑。