scholarly journals 227 Direct Numerical Simulation for Homogeneous MHD Turbulence under External Force and Uniform Magnetic Field

2014 ◽  
Vol 2014.63 (0) ◽  
pp. _227-1_-_227-2_
Author(s):  
Masayoshi OKAMOTO
1998 ◽  
Vol 358 ◽  
pp. 299-333 ◽  
Author(s):  
OLEG ZIKANOV ◽  
ANDRE THESS

The transformation of initially isotropic turbulent flow of electrically conducting incompressible viscous fluid under the influence of an imposed homogeneous magnetic field is investigated using direct numerical simulation. Under the assumption of large kinetic and small magnetic Reynolds numbers (magnetic Prandtl number Pm[Lt ]1) the quasi-static approximation is applied for the computation of the magnetic field fluctuations. The flow is assumed to be homogeneous and contained in a three-dimensional cubic box with periodic boundary conditions. Large-scale forcing is applied to maintain a statistically steady level of the flow energy. It is found that the pathway traversed by the flow transformation depends decisively on the magnetic interaction parameter (Stuart number). If the magnetic interaction number is small the flow remains three-dimensional and turbulent and no detectable deviation from isotropy is observed. In the case of a strong magnetic field (large magnetic interaction parameter) a rapid transformation to a purely two-dimensional steady state is obtained in agreement with earlier analytical and numerical results for decaying MHD turbulence. At intermediate values of the magnetic interaction parameter the system exhibits intermittent behaviour, characterized by organized quasi-two-dimensional evolution lasting several eddy-turnover times, which is interrupted by strong three-dimensional turbulent bursts. This result implies that the conventional picture of steady angular energy transfer in MHD turbulence must be refined. The spatial structure of the steady two-dimensional final flow obtained in the case of large magnetic interaction parameter is examined. It is found that due to the type of forcing and boundary conditions applied, this state always occurs in the form of a square periodic lattice of alternating vortices occupying the largest possible scale. The stability of this flow to three-dimensional perturbations is analysed using the energy stability method.


Author(s):  
Zhiqiang Xu ◽  
Xinqian Bo ◽  
Heng Wu ◽  
Zhifa Tang ◽  
Feng Chen ◽  
...  

Abstract Under the action of an external magnetic field, the magnetic particles will be arranged along the direction of the magnetic field. The laws of physics that control these processes are well described in the literature. However, when the magnetic particles move in the fluid, the magnetic particles with different initial distances have different mutual influences, so there will be different laws of motion. Therefore, based on the motion theory of magnetic particles in Stokes fluid, this article discusses the motion law of the contact and separation of two circular magnetic particles in Newtonian fluid. First, we conduct theoretical and simulation modeling of two magnetic particles under the action of a uniform magnetic field, and verify the correctness of the simulation through experiments; secondly, we use numerical simulation to study the angle of repulsion and attraction of magnetic particles at different initial distances, and analyze at the same time the changes in the trajectory, speed, torque and force of magnetic particles in the process of motion are studied. Finally, the influence of external field conditions on the phenomenon of contact and separation of magnetic particles is studied. The study found that even when the initial angle between the magnetic particles is 90° with the direction of the magnetic field, the magnetic particles with different initial distances will repel under the action of repulsive force and then contact again and keep repelling these two states, a better explanation the reason for the agglomeration of magnetic particles at close range is explained.


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