惯性颗粒所见流场拓扑结构

本文采用直接数值模拟的方法从颗粒所见的流场拓扑结构这一角度探讨了颗粒在不同拓扑结构下速度统计特性.结果表明,不同惯性的颗粒所见流体的速度特性类似,在Top1和Top2结构中,随时间演化而减少,而在Top3和Top4结构中随时间有波浪性的增长;由于颗粒惯性的差异引起的轨道交叉效应不同,颗粒与颗粒所见流体速度的关联随颗粒增大而衰减加剧,在颗粒与流体相之间的能量传递中,不同拓扑结构明显不同,从颗粒加入时能量由颗粒相向流体传递,各拓扑结构的相对强度为Top2>Top4>Top1>Top3,演化到后期能量由流体相向颗粒相传递,相对强度为Top1>Top2>Top3>Top4;st=1.0和st=10.0的颗粒差别在于演化后期Top2和Top3相对强度的转变.     

颗粒惯性对标量混合的影响

本文采用直接数值模拟的方法,研究了颗粒惯性对均匀各向同性湍流场中被动标量混合特性的影响.结果表明:与无颗粒算例相比,Tp/Tk<1的小颗粒,增大了标量脉动在高波数上的能量,增强了标量耗散率,标量耗散率最大高出了25%;Tp/Tk>1的大颗粒,在初期显著削弱了标量脉动强度,同时也加快了标量耗散率的衰减,标量脉动强度降低了约15%,标量耗散减少了约5%;而Tp/Tk=1的临界颗粒,对标量场混合的影响较弱,标量脉动强度和标量耗散偏差在5%以内;此外,随着颗粒惯性的增大,标量耗散率的概率密度函数向左平移,但分布特征的改变并不显著.     

Scalar Statistics along Inertial Particle Trajectory in Isotropic Turbulence

The statistics of a passive scalar along inertial particle trajectory in homogeneous isotropic turbulence with a mean scalar gradient is investigated by using direct numerical simulation. We are interested in the influence of particle inertia on such statistics, which is crucial for further understanding and development of models in non-isothermal gas-particle flows. The results show that the scalar variance along particle trajectory decreases with the increasing particle inertia firstly; when the particle＇s Stokes number St is less than 1.0, it reaches the minimal value when St is around 1.0, then it increases if St increases further. However, the scalar dissipation rate along the particle trajectory shows completely contrasting behavior in comparison with the scalar variance. The mechanical-to-thermal time scale ratios averaged along particle, （r）p, are approximately two times smaller than that computed in the Eulerian frame r, and stay at nearly 1.77 with a weak dependence on particle inertia. In addition, the correlations between scalar dissipation and flow structure characteristics along particle trajectories, such as strain and vorticity, are also computed, and they reach their maximum and minimum, 0.31 and 0.25, respectively, when St is around 1.0.