DNS of turbulent channel flows under magnetic fields*

The inductionless version of the magnetohydrodynamics is implemented in the Nek5000 spectral code, and it is employed to numerically investigate turbulent channels with friction Reynolds numbers varying from 140 to 1120 under a magnetic field at different Hartmann numbers. The implementation is validated for the Hartmann problem with the Hartmann number up to 100,000. The effects of the Lorentz force on the boundary layers and Reynolds stresses are investigated. The Lorentz force induced from the magnetic field is found to suppress turbulence intensities and Reynolds stresses. An increase in the magnetic field magnitude leads to increase in drag and, consequently, a larger pressure drop. The difference between production and dissipation in the turbulent kinetic energy decreased with increasing Hartmann number at the central region and large-scale structures at this region were reduced. The flow invariants are computed and the changes in flow topology due to the magnetic field are discussed in detail. The DNS results will be used as a code-to-code comparison and for the development of closures models for the high-fidelity code being developed at ORNL called VERTEX.