The effect of a transverse magnetic field on shear turbulence

Abstract

Turbulence measurements under the influence of a transverse magnetic field have been made at Purdue University's Magneto-Fluid-Mechanic Laboratory in a high aspect ratio channel. The Reynolds number range covered was 25000 ≤ Re 282000; the geometry and experimental conditions were such that the experiment approximated turbulent Hartmann flow. The aspect ratio of the channel was 5·8:1, its walls were electrically insulated and the working fluid was mercury. Measurements in the presence of a magnetic field were made of the skin friction coefficient, the mean velocity profiles, the turbulence intensity profiles (both u’ and v’) and the Reynolds stress profiles.A sudden change in the damping of the Reynolds stresses was manifested by a ‘hump’ in the curves of Cf versus M/Re taken with the Reynolds number held constant. This ‘hump’ occurs as a gentle rise and sudden drop to the Hartmann laminar line of the Cf data. Close examination of the $\overline{u^{\prime}v^{\prime}}$ data near the wall confirms this behaviour, indicating that the turbulent contribution to the shear stress is the controlling factor in this behaviour of Cf. The Reynolds stresses were completely suppressed to zero at high values of the magnetic field, though the turbulence intensities of u’ and v’ were not. The Reynolds stress data are fundamental in revealing the mechanisms which are at work during the suppression of turbulence by a magnetic field.It was also found that at high magnetic fields, when most of the turbulence was damped, the skin friction coefficient fell below the values predicted by Hartmann's (1937) laminar solution for high values of M/Re. This result was linked to the presence of ‘M-shaped’ velocity profiles in the direction perpendicular to both the magnetic field and the mean velocity vector. The presence of ‘M-shaped’ profiles has not previously been linked to a reduction in Cf.

DNS and k–ɛ model simulation of MHD turbulent channel flows with heat transfer

“…1b, the wall shear stress shows a temporal intermittency which has very long periodic time (∼10,000) at Ha = 13.0, and the flow also becomes laminar at Ha = 13.2. As the results, the maximum Ha maintaining turbulence is found to be almost 13.0 [Ha/(2Re c ) × 10 4 = 23.2] and this value is very close to the previous studies [2,7]. results [4,7], therefore the accuracy of the present DNS has been confirmed.…”

“…MHD turbulent wall-bounded flows have been investigated extensively by both experimental and numerical studies (Reed and Lykoudis [2], Simomura [3], Noguchi et al [4], Orlandi [5], Satake et al [6], Lee and Choi [7], etc.) and many important information about the drag reduction and the turbulent modulation have been obtained.…”

Energy spectra and turbulence generation in the wake of magnetic obstacles

“…In great number of industrial applications where the electrically conductive fluids are used (e.g., crystal growth, heat exchangers, latest generation of fusion reactors), heat transfer plays a central role. Generic examples also include fully developed turbulent channel flows subjected to uniform magnetic fields of different orientations (Brouillette and Lykoudis, 6 Reed and Lykoudis, 7 Shimomura, 8 Lee and Choi, 9 Kenjereš et al, 10 Boeck et al 11 ) and electromagnetically driven multiscale isothermal shallow (Rossi et al, 12,13 Lardeau et al, 14 Rossi et al, 15 Akkermans et al, 16 Duran-Matute et al 17 ) or deep (Kenjereš et al 18 ) layers with heat transfer ). The flow of electrically conducting fluids where there is an internal blockage can be generally divided into two categories.…”

An approach to verification and validation of MHD codes for fusion applications

“…Table IV. Parameters of the benchmark problem D1 for turbulent flow in a duct with uniform magnetic field [27]. The Reynolds and Hartmann numbers are based on the hydraulic diameter and mean velocity as the typical scales.…”

“…The Reynolds and Hartmann numbers are based on the hydraulic diameter and mean velocity as the typical scales. The experiment [27] is suggested as a benchmark. In this experiment, flow in a duct of aspect ratio 5.82 is subject to a uniform magnetic field on the length of 21 hydraulic diameters.…”