在牵伸和流动不稳定性背景下实验室实验中的稠密粒子云
Dense Particle Clouds in Laboratory Experiments in Context of Drafting and Streaming Instability
摘要：
流动不稳定性，作为一个例子的不稳定性驱动的粒子反馈的气体流动，已被证明有一个主要的作用，在控制形成的星子。在这里，我们提出的实验，以接近这种情况下，在实验室中的克努森流动制度的颗粒。在这些实验中，我们观察到一个粒子云被困在一个旋转系统在地球引力下约30秒。当平均尘气比高达0.08时，颗粒的行为就像单个测试颗粒一样。它们的沉降速度与单个自由下落粒子的沉降速度相同，即使在局部密度较高的区域也是如此。然而，对于更高的尘气比，颗粒的运动变得敏感的结块。粒子在局部密度较大的区域沉积得更快。然后，它们的沉降速度线性地取决于总的粉尘与气体的比率。这清楚地表明了从跟踪行为到集体行为的转变。除了这些发现之外，这些类型的实验现在可以作为一种衡量标准来测试天体物理学流体力学中的粒子反馈模型，这些模型目前用于流不稳定性的数值模拟。
英文摘要：
The streaming instability, as an example of instabilities driven by particle feedback on a gas flow, has been proven to have a major role in controlling the formation of planetesimals. Here, we present experiments to approach this situation in the laboratory for particles in the Knudsen flow regime. In these experiments, we observe a particle cloud trapped for about 30 s in a rotating system under Earth's gravity. For average dust-to-gas ratios up to 0.08, particles behave like individual test particles. Their sedimentation speed is identical to that of a single free-falling particle, even in locally denser regions. However, for higher dust-to-gas ratios, the motion of particles becomes sensitive to clumping. Particles in locally denser regions now sediment faster. Their sedimentation speed then depends linearly on the overall dust-to-gas ratio. This clearly shows a transition from tracerlike behavior to collective behavior. Beyond these findings, these types of experiments can now be used as a gauge to test the particle feedback models in astrophysical hydrocodes which are currently used for numerical simulations of streaming instabilities.
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