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LARGE EDDY SIMULATION OF TURBULENT DUCT FLOWS IN A LIQUID METAL MHD GENERATOR WITH NON-UNIFORM MAGNETIC FIELD

Hiromichi Kobayashi
Center for Turbulence Research, Stanford University Stanford, California 94305-3035, USA and Department of Physics, Keio University 4-1-1, Hiyoshi, Kohoku-ku, Yokohama, 223-8521, Japan

Hiroki Shionoya
Department of Energy Sciences Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan

Yoshihiro Okuno
Department of Energy Sciences, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan

Аннотация

Large-eddy simulation (LES) of the turbulent duct flows in a liquid metal magnethydrodynamic (MHD) power generator is examined to reveal the behavior of the MHD flows and the turbulent structures. The non-uniform magnetic flux density in the streamwise direction produces two eddy currents. The eddy current causes the wall-jet flows with M-shaped mean streamwise velocity profiles in the direction parallel to the external magnetic field. In contrast, the Hartmann flows with the flattened velocity profiles by the Lorentz force are produced in the direction perpendicular to the external magnetic field. In the case of the strong magnetic flux density, the turbulence structures similar to the Karman vortex sheets emerge in the downstream duct. The coherent structure model, one of the subgrid-scale models, well represents the relaminarization by the Lorentz force in comparison with the Smagorinsky model with the Van Driest's wall function. Turbulence intensities decrease under the magnetic field, but in the wall jet flows, the streamwise one is enhanced.