碰撞流中的冷却和不稳定性
Cooling and Instabilities in Colliding Flows
摘要：
发生在原恒星喷流中的碰撞自相互作用会产生强烈的激波，其结构会受到流内辐射冷却的影响。为了研究这种碰撞流，我们使用AstroBEAR AMR代码进行一维和三维的幂律冷却功能的流体动力学模拟。冷却的特征长度和时间尺度取决于温度，因此可以随着冲击气体冷却而变化。当冷却长度足够快地减小时，系统变得不稳定，产生辐射激波不稳定性，在激波阵面位置产生振荡;这些振荡可以在一维和三维情况下看到。我们的模拟表明，没有证据表明密度聚集特性的热不稳定性，即使当冷却功能满足预期的标准。在三维的情况下，非线性薄壳不稳定性（NTSI）被发现占主导地位时，冷却长度是足够小的。当流动受到辐射激波不稳定性，振荡的冷却区域的大小允许NTSI发生在更大的冷却长度，虽然更大的冷却长度延迟NTSI的发病增加振荡周期。
英文摘要：
Collisional self-interactions occurring in protostellar jets give rise to strong shocks, the structure of which can be affected by radiative cooling within the flow. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in both one and three dimensions with a power law cooling function. The characteristic length and time scales for cooling are temperature dependent and thus may vary as shocked gas cools. When the cooling length decreases sufficiently rapidly the system becomes unstable to the radiative shock instability, which produces oscillations in the position of the shock front; these oscillations can be seen in both the one and three dimensional cases. Our simulations show no evidence of the density clumping characteristic of a thermal instability, even when the cooling function meets the expected criteria. In the three-dimensional case, the nonlinear thin shell instability (NTSI) is found to dominate when the cooling length is sufficiently small. When the flows are subjected to the radiative shock instability, oscillations in the size of the cooling region allow NTSI to occur at larger cooling lengths, though larger cooling lengths delay the onset of NTSI by increasing the oscillation period.
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