标题： 湍流分子云中尘埃颗粒的动力学。解耦条件及不同数值实现的限制 显示英文标题

标题： Dynamics of dust grains in turbulent molecular clouds. Conditions for decoupling and limits of different numerical implementations

摘要： 分子云中尘埃颗粒的动力学由其与超音速湍流气体运动的相互作用所调控。尘埃颗粒从气体动力学中解耦的条件仍缺乏明确约束。我们首先旨在通过理论预测和数值实验来研究动力学解耦的关键尘埃颗粒尺寸。其次，我们旨在确定两种根本不同的数值方法在湍流分子云中尘埃和气体混合物演化的适用范围。我们使用两种不同的方案进行了一系列数值实验。首先，在终端速度近似（TVA）下，我们在欧拉网格上使用单流体形式。其次，我们使用双流体方案，其中尘埃动力学通过拉格朗日超粒子处理，而气体动力学则在欧拉网格上处理。单流体结果与理论上的解耦临界尺寸相符。我们报告了斯托克斯数St>0.1时的尘埃动力学解耦，即尺寸为$s>4~\mu$米的尘埃颗粒。我们发现，TVA适用于分子云中尺寸为10$\mu$米的颗粒，尤其是在最致密的区域。然而，在St>1的低密度物质中测得的最大尘埃富集度值得怀疑。在拉格朗日尘埃实验中，我们表明所有尘埃颗粒尺寸的结果都受到数值方法的影响。对于St<<1的情况，尘埃动力学主要受到高密度区域中的人工捕获影响，导致尘埃浓度出现虚假变化。对于St>1的情况，最大尘埃富集度由用于气体动力学的网格分辨率决定。因此，应根据本研究中强调的限制重新审视以前类似数值工作的结果。亚微米尘埃颗粒在分子云最致密的部分不太可能发生尘埃富集。 显示英文摘要

摘要： Dust grain dynamics in molecular clouds is regulated by its interplay with supersonic turbulent gas motions. The conditions under which dust grains decouple from the dynamics of gas remain poorly constrained. We first aim to investigate the critical dust grain size for dynamical decoupling, using both analytical predictions and numerical experiments. Second, we aim to set the range of validity of two fundamentally different numerical implementations for the evolution of dust and gas mixtures in turbulent molecular clouds. We carried out a suite of numerical experiments using two different schemes. First, we used a monofluid formalism in the terminal velocity approximation (TVA) on a Eulerian grid. Second, we used a two-fluid scheme, in which the dust dynamics is handled with Lagrangian super-particles, and the gas dynamics on a Eulerian grid. The monofluid results are in good agreement with the theoretical critical size for decoupling. We report dust dynamics decoupling for Stokes number St>0.1, that is, dust grains of $s>4~\mu$m in size. We find that the TVA is well suited for grain sizes of 10 $\mu$m in molecular clouds, in particular in the densest regions. However, the maximum dust enrichment measured in the low-density material where St>1 is questionable. In the Lagrangian dust experiments, we show that the results are affected by the numerics for all dust grain sizes. At St<<1, the dust dynamics is largely affected by artificial trapping in the high-density regions, leading to spurious variations of the dust concentration. At St>1, the maximum dust enrichment is regulated by the grid resolution used for the gas dynamics. The results of previous similar numerical work should therefore be revisited with respect to the limitations we highlight in this study. Dust enrichment of submicron dust grains is unlikely to occur in the densest parts of molecular clouds.