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首页> 外文期刊>Geophysical and Astrophysical Fluid Dynamics >The dynamics of two interacting compositional plumes in the presence of a magnetic field
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The dynamics of two interacting compositional plumes in the presence of a magnetic field

机译：磁场作用下两个相互作用的成分羽的动力学

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摘要

The dynamics of two compositionally buoyant columns of fluid rising in an infinite less buoyant fluid is studied in the presence of a uniform magnetic field, B _0. The fluid is thermally stably stratified and has a viscosity, ν, a thermal diffusivity, k and magnetic diffusivity, η. The stability of the mean state to infinitesimal disturbances is governed by the seven dimensionless parameters: the Reynolds number, R (= UL/ν, where U, L are characteristic velocity and length respectively) which measures the strength of the compositional buoyancy; the dimensionless measures x _0, x _1, d of the thickness of the two plumes and the distance between them, respectively; the ratio Y of the strengths of the two plumes (as measured by their basic concentration of light material); the Chandrasekhar number, Qc (=B _0~2L ~2/μρ0ην, in which μ is the magnetic permeability, p0 the fluid density and B _0 a characteristic unit of magnetic field), is a measure of the magnitude of the magnetic field and the normalized horizontal projection B?H = sinθ of the magnetic field, where 8 measures the inclination of the magnetic field to the vertical. The stability is examined for small values of R. The preferred mode of instability is studied in the parameter space (x _0, x _1,d,T, Qc, B?H). It is shown that the influence of the magnetic field does not change the order of the magnitude of the growth rate from O(R ~o) of the two non-magnetic interacting plumes and it does not introduce any new modes to the stability problem. However, the presence of the magnetic field introduces novel features to the stability problem. For any fixed set x _0, x _1, d, Y, Qc, the growth rate can either increase with B?H or initially decrease reaching a minimum before it increases again. As Qc increases, with x _0, x _1, d, Y, B?H fixed, the growth rate can assume one of four different behaviours: (i) it maintains the same value of the non-magnetic case with the disturbance propagating along field lines; (ii) it decreases steadily with Qc; (iii) it maintains the same value as in the absence of the field until a value Qcm(x _0, x _1, d, γ, B?H) is reached when it starts to increase to a maximum before it decreases to zero for large values of Qc and (iv) it increases from its value for Qc = 0 reaching a maximum before it decreases steadily to zero at some value of Qc dependent on the other parameters. The helicity and a-effect have also been studied to find that the unstable motions can produce mean helicity and α-effect.
机译：在均匀磁场B _0的存在下，研究了在无限少浮力的流体中上升的两根组成浮力的流体的动力学。该流体被热稳定地分层并且具有粘度ν，热扩散率k和磁扩散率η。平均状态对无穷小扰动的稳定性由七个无量纲参数控制：雷诺数R（= UL /ν，其中U，L分别为特征速度和长度），用于测量成分浮力的强度;两个羽的厚度的无量纲度量x _0，x _1，d以及它们之间的距离;两个羽流的强度之比Y（由其轻质材料的基本浓度测量）; Chandrasekhar数Qc（= B _0〜2L〜2 /μρ0ην，其中μ是磁导率，p0是流体密度，B _0是磁场的特征单位），是磁场强度的度量，并且归一化水平投影B？H =磁场的sinθ，其中8表示磁场相对于垂直方向的倾斜度。对于较小的R值，检查稳定性。在参数空间（x _0，x _1，d，T，Qc，B？H）中研究首选的不稳定性模式。结果表明，磁场的影响不会改变两个非磁性相互作用羽的O（R〜o）增长率的大小顺序，并且不会为稳定性问题引入任何新的模式。然而，磁场的存在为稳定性问题引入了新颖的特征。对于任何固定集x _0，x _1，d，Y，Qc，增长率可以随B？H的增加而增加，也可以先下降到最小值，然后再增加。随着Qc的增加，在x _0，x _1，d，Y，B？H固定的情况下，增长率可以假定为四种不同的行为之一：（i）在扰动沿传播的情况下，它保持非磁性情况的相同值场线; （ii）随着Qc稳定下降; （iii）它保持与不存在字段时相同的值，直到当它开始增加到最大值并在减小到零之前达到最大值Qcm（x _0，x _1，d，γ，B？H）为止。较大的Qc值（iv）从Qc = 0的值增加到最大值，然后在取决于其他参数的某个Qc值稳定减小到零之前。还研究了螺旋度和α效应，发现不稳定运动会产生平均螺旋度和α效应。

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