Dust Coagulation Regulated by Turbulent Clustering in Protoplanetary Disks
Dust Coagulation Regulated by Turbulent Clustering in Protoplanetary Disks
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DOI：
10.3847/1538-4357/aaa976
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发表时间：
2018-01
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影响因子：
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通讯作者：
T. Ishihara;Naoki Kobayashi;Kei Enohata;M. Umemura;K. Shiraishi
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作者：
T. Ishihara;Naoki Kobayashi;Kei Enohata;M. Umemura;K. Shiraishi
尘埃颗粒的凝聚是星子形成的关键过程。然而，径向漂移和反弹障碍尚未完全解决，特别是对于硅酸盐尘埃。由于尘埃颗粒的碰撞速度受原行星盘中湍流的调节，应当妥善处理湍流聚集问题。为此，对纳维 - 斯托克斯方程进行直接数值模拟（DNS）是必要的。在一系列论文中，潘和帕多安使用了雷诺数Re∼1000的DNS。在此，我们进行了雷诺数高达Re = 16100的DNS，这使我们能够在惯性范围内追踪斯托克斯数为0.01≲St≲0.2的颗粒的运动。通过DNS，我们证实，与奥尔梅尔和库齐的结果相比，颗粒对的均方根相对速度小了两倍多。径向相对速度的分布高度非高斯分布。在低雷诺数下，结果与潘和帕多安或潘等人的结果基本一致。此外，我们发现等大小颗粒的黏附率远高于不同大小颗粒的黏附率。即使在α - 黏度为10⁻²的强湍流情况下，对于斯托克斯数≲0.01的等大小颗粒，黏附率高达≳50%，反弹概率低至∼10%。因此，湍流聚集在厘米级致密聚集体（卵石）的生长中起着重要作用，并且还提高了固体丰度，这可能导致盘中的流不稳定性。
The coagulation of dust particles is a key process in planetesimal formation. However, the radial drift and bouncing barriers are not completely resolved, especially for silicate dust. Since the collision velocities of dust particles are regulated by turbulence in a protoplanetary disk, turbulent clustering should be properly treated. To that end, direct numerical simulations (DNSs) of the Navier–Stokes equations are requisite. In a series of papers, Pan & Padoan used a DNS with Reynolds number Re ∼ 1000. Here, we perform DNSs with up to Re = 16,100, which allow us to track the motion of particles with Stokes numbers of 0.01 ≲ St ≲ 0.2 in the inertial range. Through the DNSs, we confirm that the rms relative velocity of particle pairs is smaller by more than a factor of two, compared to that by Ormel & Cuzzi. The distributions of the radial relative velocities are highly non-Gaussian. The results are almost consistent with those by Pan & Padoan or Pan et al. at low Re. Also, we find that the sticking rates for equal-sized particles are much higher than those for different-sized particles. Even in the strong-turbulence case with α-viscosity of 10−2, the sticking rates are as high as ≳50% and the bouncing probabilities are as low as ∼10% for equal-sized particles of St ≲ 0.01. Thus, turbulent clustering plays a significant role in the growth of centimeter-sized compact aggregates (pebbles) and also enhances the solid abundance, which may lead to the streaming instability in a disk.