Droplet–turbulence interactions in low-Mach-number homogeneous shear two-phase flows
Droplet–turbulence interactions in low-Mach-number homogeneous shear two-phase flows
复制标题
低马赫数均匀剪切两相流中的液滴-湍流相互作用
DOI：
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发表时间：
1998
影响因子：
3.7
通讯作者：
F. Mashayek
中科院分区：
文献类型：
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作者：
F. Mashayek
通过直接数值模拟（DNS）研究了与湍流中液滴的分散性和多分散性有关的几个重要问题。在欧拉环境中考虑载波相位，在拉格朗日框架中跟踪分散相，并在实际的双向（耦合）公式中考虑相位之间的相互作用。由此产生的方案适用于低马赫数、充满液滴的均匀剪切湍流的广泛 DNS。对于非蒸发和蒸发液滴，考虑了几种单向和双向耦合的情况。研究了质量加载比、液滴时间常数和热力学参数（例如液滴比热、液滴蒸发潜热和沸腾温度）对湍流和液滴的影响。还研究了初始液滴温度和载体相中初始蒸气质量分数的影响。不考虑重力效应，因为数值方法仅适用于没有重力的情况。通过分析输运方程中的各项，研究了湍流动能和两相平均内能的演变。非蒸发液滴的结果表明，液滴的存在降低了载相的湍流动能，同时增加了流动的各向异性水平。液滴流向速度方差大于流体速度方差，且两者之比随着液滴时间常数的增大而增大。蒸发通过传质增加了湍流动能和载体相的平均内能。一般来说，当相之间的初始温差可以忽略不计时，蒸发由液滴周围的蒸气质量分数梯度控制。另一方面，在初始液滴温度较小的情况下，对流换热在蒸发过程中更为重要。在很长一段时间内，蒸发速率根据各种参数的值接近渐近值。结果表明，存在于流动的高应变率区域的液滴的蒸发速率较大，这主要是由于这些区域中的液滴雷诺数较大。对于蒸发和非蒸发液滴，两相温度波动的均方根（rms）在很长一段时间内变得与初始液滴温度无关。还讨论了与充满液滴的湍流建模相关的一些问题。
Several important issues pertaining to dispersion and polydispersity of droplets in turbulent flows are investigated via direct numerical simulation (DNS). The carrier phase is considered in the Eulerian context, the dispersed phase is tracked in the Lagrangian frame and the interactions between the phases are taken into account in a realistic two-way (coupled) formulation. The resulting scheme is applied for extensive DNS of low-Mach-number, homogeneous shear turbulent flows laden with droplets. Several cases with one- and two-way couplings are considered for both non-evaporating and evaporating droplets. The effects of the mass loading ratio, the droplet time constant, and thermodynamic parameters, such as the droplet specific heat, the droplet latent heat of evaporation, and the boiling temperature, on the turbulence and the droplets are investigated. The effects of the initial droplet temperature and the initial vapour mass fraction in the carrier phase are also studied. The gravity effects are not considered as the numerical methodology is only applicable in the absence of gravity. The evolution of the turbulence kinetic energy and the mean internal energy of both phases is studied by analysing various terms in their transport equations. The results for the non-evaporating droplets show that the presence of the droplets decreases the turbulence kinetic energy of the carrier phase while increasing the level of anisotropy of the flow. The droplet streamwise velocity variance is larger than that of the fluid, and the ratio of the two increases with the increase of the droplet time constant. Evaporation increases both the turbulence kinetic energy and the mean internal energy of the carrier phase by mass transfer. In general, evaporation is controlled by the vapour mass fraction gradient around the droplet when the initial temperature difference between the phases is negligible. In cases with small initial droplet temperature, on the other hand, the convective heat transfer is more important in the evaporation process. At long times, the evaporation rate approaches asymptotic values depending on the values of various parameters. It is shown that the evaporation rate is larger for droplets residing in high-strain-rate regions of the flow, mainly due to larger droplet Reynolds numbers in these regions. For both the evaporating and the non-evaporating droplets, the root mean square (r.m.s.) of the temperature fluctuations of both phases becomes independent of the initial droplet temperature at long times. Some issues relevant to modelling of turbulent flows laden with droplets are also discussed.