Finite-size evaporating droplets in weakly compressible homogeneous shear turbulence
Finite-size evaporating droplets in weakly compressible homogeneous shear turbulence
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DOI：
10.1017/jfm.2021.1140
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发表时间：
2021-04
影响因子：
3.7
通讯作者：
N. Scapin;F. Dalla Barba;Giandomenico Lupo;M. Rosti;C. Duwig;L. Brandt
中科院分区：
文献类型：
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作者：
N. Scapin;F. Dalla Barba;Giandomenico Lupo;M. Rosti;C. Duwig;L. Brandt
摘要本文对弱可压缩均匀剪切湍流中有限尺寸蒸发液滴进行了界面解析模拟。研究通过改变三个无维物理参数进行：临界温度以上的初始气体温度$T_{g,0}/T_c$，柯尔莫戈罗夫尺度以上的初始液滴直径$d_0/\eta$和表面张力，即基于剪切的韦伯数$We_{\mathcal {S}}$。对于最小的$We_{\mathcal {S}}$，我们首先讨论了用于评估气体热物理性质的三种热力学模型对蒸发速率的影响：一种恒定性质模型和两种允许气体密度或所有气体性质变化的变性质方法。以最后一种方法为参考，假设气体性质不变并使用“1/3”规则评估的模型比气体密度唯一可变性质的模型更能预测蒸发速率。此外，我们观察到众所周知的Frössling/Ranz-Marshall相关性低估了低温下的Sherwood数，$T_{g,0}/T_c=0.75$。接下来，我们证明了湍流中实际蒸发速率与停滞条件下计算的蒸发速率之比总是远远高于弱变形液滴的蒸发速率之比：它随着$T_{g,0}/T_c$而减小，而在考虑的最高$T_{g,0}/T_c$时却没有接近于1。这表明，在典型的燃烧应用条件下，湍流也会导致蒸发增强。最后，我们研究了在较高的$We_{\mathcal {S}}$处的总蒸发速率和局部界面质量通量，发现蒸发速率与界面曲率呈正相关，特别是在最低的$T_{g,0}/T_c$处。
Abstract We perform interface-resolved simulations of finite-size evaporating droplets in weakly compressible homogeneous shear turbulence. The study is conducted by varying three dimensionless physical parameters: the initial gas temperature over the critical temperature $T_{g,0}/T_c$, the initial droplet diameter over the Kolmogorov scale $d_0/\eta$ and the surface tension, i.e. the shear-based Weber number, $We_{\mathcal {S}}$. For the smallest $We_{\mathcal {S}}$, we first discuss the impact on the evaporation rate of the three thermodynamic models employed to evaluate the gas thermophysical properties: a constant property model and two variable-properties approaches where either the gas density or all the gas properties are allowed to vary. Taking this last approach as reference, the model assuming constant gas properties and evaluated with the ‘1/3’ rule is shown to predict the evaporation rate better than the model where the only variable property is the gas density. Moreover, we observe that the well-known Frössling/Ranz-Marshall correlation underpredicts the Sherwood number at low temperatures, $T_{g,0}/T_c=0.75$. Next, we show that the ratio between the actual evaporation rate in turbulence and the one computed in stagnant conditions is always much higher than one for weakly deformable droplets: it decreases with $T_{g,0}/T_c$ without approaching unity at the highest $T_{g,0}/T_c$ considered. This suggests an evaporation enhancement due to turbulence also in conditions typical of combustion applications. Finally, we examine the overall evaporation rate and the local interfacial mass flux at higher $We_{\mathcal {S}}$, showing a positive correlation between evaporation rate and interfacial curvature, especially at the lowest $T_{g,0}/T_c$.