Three-dimensional Magnetohydrodynamic Simulations of Radiatively Cooling, Pulsed Jets
Three-dimensional Magnetohydrodynamic Simulations of Radiatively Cooling, Pulsed Jets
复制标题
辐射冷却脉冲射流的三维磁流体动力学模拟
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
E. M. de Gouveia Dal Pino
中科院分区：
文献类型：
--
作者：
A. Cerqueira;E. M. de Gouveia Dal Pino
在这里，我们调查，通过全三维光滑粒子磁流体动力学数值模拟，不同的初始磁场配置的过密，辐射冷却，脉冲射流的演变，使用以下不同的初始磁场拓扑结构的影响：（1）纵向的，（2）既渗透射流又渗透周围介质的螺旋几何形状，以及（3）仅渗透射流的纯环形几何形状。我们探讨了不同的脉动周期，以及不同的磁场强度值（β <$0.1-∞或B <$260 -0 μG）的影响。螺旋或环形场的存在往往比纵向场更能影响流体的全局特性。然而，先前在涉及不同磁场配置的二维模拟中检测到的相对差异在三维流中被减小。虽然环形磁性部件的存在可以改变靠近喷射头的形态，抑制其在喷射的早期演变中的破碎，如先前在文献中所报道的，但是脉冲诱导的内部结的影响导致cloudron的出现，复杂的形态在射流头（所需的赫比格-哈罗[HH]射流的观察），即使在MHD射流模型与螺旋或环形配置。内部工作表面的详细结构和发射特性也可以通过磁场的存在而显著改变。磁场强度的增加（β的减小）改善了喷流的准直性，并放大了具有螺旋场和β相对于螺旋喷流为1-0.1的喷流结后面的密度（最多放大1.4和4倍）和Hα强度（最多放大4和5倍）。因此，相应的I[S II]/IHα比值（经常用于确定HH天体的激发能级）在具有环形分量的MHD模型中可以相对于THD计算减少大约相同的量，尽管上面的强度估计非常近似。我们还发现，在具有螺旋磁场的MHD模型中，可以触发Kelvin-Helmholtz不稳定性的螺旋模式，导致喷流轴的一些摆动。在三维流动中，甚至在β = 0.1的情况下，都没有发现在具有初始环形磁场的二维喷流模拟中通常检测到的鼻锥形成的证据。我们的研究结果HH喷气机的影响进行了简要讨论。
We here investigate, by means of fully three-dimensional smoothed particle magnetohydrodynamic numerical simulations, the effects of different initial magnetic field configurations on the evolution of overdense, radiatively cooling, pulsed jets using the following different initial magnetic field topologies: (1) longitudinal, (2) helical geometry permeating both the jet and the ambient medium, and (3) purely toroidal geometry permeating the jet only. We explore the effects of different pulsational periods, as well as different values of the magnetic field strength (β ≃ 0.1-∞ or B ≃ 260-0 μG). The presence of a helical or toroidal field tends to affect the global characteristics of the fluid more than a longitudinal field. However, the relative differences that have been previously detected in two-dimensional simulations involving distinct magnetic field configurations are diminished in the three-dimensional flows. While the presence of toroidal magnetic components can modify the morphology close to the jet head, inhibiting its fragmentation in the early evolution of the jet, as previously reported in the literature, the impact of the pulse-induced internal knots causes the appearance of a clumpy, complex morphology at the jet head (as required by the observations of Herbig-Haro [HH] jets) even in the MHD jet models with helical or toroidal configurations. The detailed structure and emission properties of the internal working surfaces can also be significantly altered by the presence of magnetic fields. The increase of the magnetic field strength (decrease of β) improves the jet collimation and amplifies the density (by factors up to 1.4 and 4) and the Hα intensity (by factors up to 4 and 5) behind the knots of jets with a helical field and β ≃ 1-0.1 relative to a nonmagnetic jet. As a consequence, the corresponding I[S II]/IHα ratio (which is frequently used to determine the excitation level of HH objects) can be decreased in the MHD models with toroidal components relative to nonmagnetic calculations by about the same amounts, although the intensity estimates above are very approximate. We also find that the helical mode of the Kelvin-Helmholtz instability can be triggered in MHD models with helical magnetic fields, causing some wiggling of the jet axis. No evidence for the formation of the nose cones that are commonly detected in two-dimensional jet simulations with initial toroidal magnetic fields is found in the three-dimensional flows or even in the β ≃ 0.1 case. The implications of our results for HH jets are briefly discussed.
影响因子：
3.2
作者：
V. Mannings;A. Boss;S. Russell
通讯作者：
V. Mannings;A. Boss;S. Russell