各向同性湍流中颗粒团簇结构及多尺度聚集效应特性研究

The morphological feature of liquid fuel vapour and its interaction with ambient turbulence affect subsequent multi-physics phenomenon, for instance, the evaporation rate depends greatly on the surface area of fuel clusters and directly links to combustion efficiency. To elucidate the mechanism of droplet fuel dispersion, the turbulence-particle interactions will be studied experimentally in a facility of the ‘box of turbulence’, which generates homogeneous and isotropic turbulence with controllable turbulent intensity. The current proposal focuses on the effect of multi-scale behaviour of particle preferential concentration. We will develop novel pattern recognition algorithm to identify the continuous morphological cluster structures. The effect of particle size distribution and turbulent scale dependent Stokes number on the clustering statistics and morphology will be evaluated, as well as the scale dependent cluster self-similarity behaviour. Simultaneous velocity measurement technique of both the carrier and the dispersed phase will be developed. the With the experimental data obtained from the current proposal, we plan to develop an open source experimental turbulence-particle database, aiming to foster collaborations between researchers with numerical and experimental methods.

液体燃料雾化过程中连续团簇结构尺度与环境流场尺度的相对关系影响耦合的多物理过程，比如液体燃料团簇表面积直接影响蒸发率，从而影响局部当量比和燃烧效率。为发展颗粒团簇结构描述方法，阐明湍流颗粒扩散机理，本申请立足于湍流度可控的各向同性两相湍流实验装置，探索较高体积数条件下两相耦合速度场测量技术，发展连续团簇结构模式识别算法，从连续团簇结构角度对颗粒多尺度聚集效应自相似特性进行研究，并系统研究与颗粒粒径d(p)以及湍流尺度τ相关斯托克斯数St（d(p),τ）对颗粒多尺度聚集效应特性的影响机制。通过本项目将初步建立两相湍流开放实验数据库，促进两相湍流研究数值计算和实验研究的结合。

项目首先发展了连续团簇结构模式识别算法，揭示了基于Voronoï方法的团簇形态学特征空间尺度自相似特性；其次，基于液滴速度场（Particle Tracking Velocimetry （PTV））测量技术，阐明了扩散相液滴相对速度及速度结构函数的尺度相关机理，研究表明扩散相液滴的宏观速度在惯性区及耗散区具有空间尺度自相似特性，扩散相液滴的二阶结构函数在惯性区具有空间尺度自相似特性，而在10-1 ~ 101η耗散尺度则表现出明显的尺度无关特性，说明液滴惯性力主导了耗散尺度的扩散相动能传递；最后，基于Voronoï分析方法，发现了液滴沉降速度u ̅΄p2/uη与团簇结构空间尺度γ具有非单调依赖规律，辅证扩散相动能传递规律在全尺度存在转换机制，耗散尺度液滴惯性力主导扩散相动能传递，而惯性区则由大尺度团簇与相应尺度流动结构动能传递关系主导。项目研究丰富了多尺度团簇结构湍流扩散流动理论。