惯性颗粒所见被动标量统计特性的直接数值模拟研究

Direct Numerical Simulation of Statistics of Passive Scalar Seen by Inertial Particle

本文采用直接数值模拟方法,对惯性颗粒所见均匀各向同性湍流中具有平均标量梯度的被动标量场统计特性进行了研究。模拟结果表明:与颗粒所见流体速度的自相关特性不同,颗粒所见标量的自相关特性随颗粒惯性的增加而单调减少;颗粒所见标量脉动能随颗粒惯性的增加先减少再增大,在St≈1.0的临界颗粒附近达到最小值,而颗粒所见标量耗散率随颗粒惯性的变化行为与颗粒所见标量脉动能的变化行为相反;数值模拟的结果进一步揭示,在St≈1.0时颗粒所见流体标量脉动能和耗散率的极值是因为St≈1.0的临界颗粒聚集于低涡量、高应变区域和标量场在高应变区域形成强耗散的片状结构所致。

In this paper,statistics of passive scalar along the trajectory of inertial particle in homogeneous isotropic turbulence was studied by the use of 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.Simulation results show that：the auto-correlation coefficient of scalar seen by particle monotonically decreases with the increase of particle inertia,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.Simulation results further revealed that the extreme values of scalar variance and dissipation at St≈1.0 result from the aggregation of critical particles in high strain,low vorticity regions and the formation of sheet structures,which are of strong scalar dissipation,in these regions.