Effects of the Compressibility of Turbulence on the Dust Coagulation Process in Protoplanetary Disks
Effects of the Compressibility of Turbulence on the Dust Coagulation Process in Protoplanetary Disks
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DOI：
10.3847/1538-4357/abe9ba
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
Yoshiki Sakurai;T. Ishihara;Hitomi Furuya;M. Umemura;K. Shiraishi
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作者：
Yoshiki Sakurai;T. Ishihara;Hitomi Furuya;M. Umemura;K. Shiraishi
星子被认为是由原行星盘湍流中的尘埃颗粒凝结而成。然而，弹跳和破碎障碍尚未完全解决，特别是对于硅酸盐粉尘。为了绕过这些障碍，必须适当处理灰尘颗粒的湍流聚集。根据最小质量太阳星云（MMSN）模型，湍流的马赫数范围为M rms ≃ 0.01–0.32，因此湍流通常被认为本质上是不可压缩的。然而，尚未定量研究不可压缩极限是否足以进行原行星盘模拟。因此，我们在本研究中比较了弱可压缩湍流和不可压缩湍流之间的纳维-斯托克斯方程的直接数值模拟（DNS）中惯性粒子的运动。在可压缩湍流的 DNS 中，我们使用外力来设置总耗散和膨胀与螺线管耗散比。 DNS显示，尽管马赫数M rms(≲0.3)很小，但可压缩湍流场在密度波动、压力波动和冲击波产生方面与不可压缩湍流场显着不同，具体取决于膨胀强迫的比率。然而，我们定量地证实，这些对粒子碰撞统计的影响很弱，并且弱可压缩湍流中惯性粒子的运动由螺线管速度分量主导。因此我们可以得出结论，不可压缩假设适用于研究原行星盘湍流中的尘埃凝聚过程，如 MMSN 模型中所假设的那样。
Planetesimals are believed to be formed by the coagulation of dust grains in the protoplanetary disk turbulence. However, the bouncing and fragmentation barriers have not been completely solved, particularly for silicate dust. To circumvent these barriers, the turbulent clustering of dust particles must be properly treated. According to the minimum-mass solar nebula (MMSN) model, the Mach number of the turbulence ranges from M rms ≃ 0.01–0.32, and thus the turbulence is often regarded as essentially incompressible. However, it has not been quantitatively investigated whether the incompressible limit is adequate for protoplanetary disk simulations. We therefore compare in this study the motions of inertial particles in direct numerical simulations (DNSs) of the Navier–Stokes equation between weakly compressible turbulence and incompressible turbulence. In the DNSs of compressible turbulence, we use an external force to set the total dissipation and the dilatational-to-solenoidal dissipation ratio. The DNSs reveal that despite the small Mach number M rms( ≲ 0.3), the compressible turbulence field notably differs from the incompressible field in terms of the density fluctuations, pressure fluctuations, and shocklet generation, depending on the ratio of the dilatational forcing. However, we quantitatively confirmed that these effects on the particle collision statistics are weak and that the motion of inertial particles in weakly compressible turbulence is dominated by the solenoidal velocity components. Therefore we can conclude that the incompressible assumption is appropriate for an investigation of the dust coagulation process in protoplanetary disk turbulence, as assumed in the MMSN model.