边界持续激励条件下颗粒气体各向异性结构、颗粒速度分布和颗粒温度的测量与研究

Anisotropic structures, such as cluster structures and vortex structures, are ubiquitous in continuously driven granular gases. The phenomena cannot be effectively described by existing granular kinetic theories and become a hot topic in current natural sciences. It is very important to develop the latest measurement methods, break through the bottleneck of testing technology and then provide reliable physical data for revealing the unique phenomena and dynamics of granular gases. In this proposal, 1) we would study the fractal topology, the criterion and characteristic factors of granular clusters after improving high-speed particle localization and recognition techniques for particulate gases. 2) we would develop the particle tracking velocimetry technique based on Voronoi diagram matching to realize the measurement of the tiny eddy field of particle gas. And then the spatial correlation between particle cluster and particle velocity field distribution would be studied alongside with its evolution with time. 3) We would improve the speckle visibility spectrum (SVS) measurement technique for granular temperature with high spatial and temporal resolution, and develop multiple SVS synchronous measurement technology to obtain the spatial correlation of particle gas flow field and the dynamic evolution law. 4) we would study the influence of different external factors on the cluster structure, velocity distribution and particle temperature of granular gas. The results of the project would be useful to judge the validity of the existing granular kinetic theories, and provide scientific guidance for the interaction of internal cluster structures and boundaries in gas-solid fluidized beds.

在持续驱动的颗粒气体中，团簇和旋涡等各向异性结构普遍存在，是当前颗粒气体理论研究的热点问题。急需借鉴和研发最新测量手段，突破测试技术瓶颈，为客观揭示颗粒气体所特有的动力学现象和规律，提供可靠数据。因此，本项目拟开展如下工作：1）完善适用于颗粒气体的高速粒子定位和识别技术，测量颗粒团簇的分形拓扑结构，研究其判定标准和特征因子；2）研究基于维诺图匹配的粒子跟踪测速技术，实现颗粒气体微小旋涡场的测量，进而研究颗粒团簇与颗粒速度场分布的空间相关性，及其随时间的演化规律；3）完善高时空分辨率散斑能见度光谱（SVS）颗粒温度测量技术，开发多台SVS同步测量技术，获取颗粒气体流场的空间关联，以及动态演化规律；4）研究不同外界因素对颗粒气体的团簇结构、速度分布和颗粒温度的影响。本项目的研究结果将便于人们确切地衡量和判断已有颗粒气体动理学的有效性，对工业气固流化床中的颗粒团簇等结构与边界作用，提供科学指导。

颗粒系统的固-液-气相变过程对泥石流生成、颗粒材料加工、风沙启动等有着广泛影响，因而受到研究者的关注。传统的颗粒运动测量技术基于图像相关性算法，使用点匹配方式追踪颗粒位移，在湿颗粒系统、颗粒团簇运动测量中存在无法识别颗粒、匹配错误率较高等问题。本项目提出V-PTV方法，使用voronoi网格算法提高颗粒的识别与定位精度，将点匹配改进为面积匹配与形状匹配，提高对类液态与类气态颗粒的运动测量精度。在V-PTV技术的基础上对颗粒系统从“类固态”至“类液态”至“类气态”的转变过程进行实验研究。在固液相变方面，研究发现颗粒系统通常在团簇的边缘开始发生缺陷，并呈现链状的缺陷对向中心蔓延。并且，颗粒发生缺陷时七相缺陷颗粒的局部体积分数显著减小，明显小于五相缺陷和六角相颗粒的局部体积分数。在液气相变方面，通过速度分布的特征参数和概率密度分布的特征参数描述颗粒系统的状态，特征参数的微分可以判断颗粒体系气液相变过程中速度分布指数的临界值。实验结果表明，在系统全局密度与振动加速度改变时，特征参数在相变过程中存在具有一致性的特征点，这说明可以通过特征参数判断颗粒系统液气相变的临界状态。

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