AbstractWe perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving, to study the generation of solenoidal velocity components and the small-scale magnetic field. We mainly focus on the effects of mean magnetic field (B0) and the sonic...
AbstractWe perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving, to study the generation of solenoidal velocity components and the small-scale magnetic field. We mainly focus on the effects of mean magnetic field (B0) and the sonic Mach number (Ms). The dependence of solenoidal ratio (i.e., ratio of solenoidal to kinetic energies) and magnetic energy density on Ms in compressively driven turbulence is already established, but that on B0 is not yet. We also consider two different driving schemes in terms of the correlation timescale of forcing vectors: a finite-correlated driving and a delta-correlated driving. Our findings are as follows. First, when we fix the value of B0, the solenoidal ratio after saturation increases as [FORMULA OMISSION] increases. A similar trend is observed for generation of magnetic field when B0 is small. Second, when we fix the value of [FORMULA OMISSION], HD and MHD simulations result in similar solenoidal ratios when B0 is not strong (say, MA ≳ 5, where MA is Alfvén Mach number). However, the ratio increases when MA ≲ 5. Roughly speaking, the magnetic energy density after saturation is a linearly increasing function of B0 irrespective of Ms. Third, generation of the solenoidal velocity component is not sensitive to numerical resolution, but that of magnetic energy density is mildly sensitive. Finally, when initial conditions are same, the finite-correlated driving always produces more solenoidal velocity and small-scale magnetic field components than the delta-correlated driving. We additionally analyze the vorticity equation to understand why higher [FORMULA OMISSION] and B0 yield a larger quantity of the solenoidal velocity component.
AbstractWe perform numerical simulations of hydrodynamic (HD) and magnetohydrodynamic (MHD) turbulence driven by compressive driving, to study the generation of solenoidal velocity components and the small-scale magnetic field. We mainly focus on the effects of mean magnetic field (B0) and the sonic Mach number (Ms). The dependence of solenoidal ratio (i.e., ratio of solenoidal to kinetic energies) and magnetic energy density on Ms in compressively driven turbulence is already established, but that on B0 is not yet. We also consider two different driving schemes in terms of the correlation timescale of forcing vectors: a finite-correlated driving and a delta-correlated driving. Our findings are as follows. First, when we fix the value of B0, the solenoidal ratio after saturation increases as [FORMULA OMISSION] increases. A similar trend is observed for generation of magnetic field when B0 is small. Second, when we fix the value of [FORMULA OMISSION], HD and MHD simulations result in similar solenoidal ratios when B0 is not strong (say, MA ≳ 5, where MA is Alfvén Mach number). However, the ratio increases when MA ≲ 5. Roughly speaking, the magnetic energy density after saturation is a linearly increasing function of B0 irrespective of Ms. Third, generation of the solenoidal velocity component is not sensitive to numerical resolution, but that of magnetic energy density is mildly sensitive. Finally, when initial conditions are same, the finite-correlated driving always produces more solenoidal velocity and small-scale magnetic field components than the delta-correlated driving. We additionally analyze the vorticity equation to understand why higher [FORMULA OMISSION] and B0 yield a larger quantity of the solenoidal velocity component.
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