Influence of Anode-Region Boundary-Layer Separation on Disk MHD-Generator Performance

A time-dependent 2-D large-eddy simulation has been carried out in order to clarify the influence of the wall profile on nonequilibrium plasma-flow behavior and disk magnetohydrodynamic (MHD)-generator performance. The numerical investigation is not limited to the divergent generator channel only, but it also includes the inlet duct. The numerical simulations examined both a straight-disk wall profile and a contoured disk wall profile for a set of possible working conditions. These results show that boundary-layer separation, which is observed to occur near the anode region of the disk MHD generator when using a straight wall profile, is successfully eliminated by the introduction of a contoured wall profile. The suppression of boundary-layer separation improves plasma properties in the generator and leads to dramatic increases in Hall parameter and electrical efficiency. Furthermore, generator performance, as defined in terms of enthalpy extraction ratio and isentropic efficiency, is significantly improved. Although the wall-profile modification might be perceived as seemingly trivial, the influence on system performance can be truly profound. Therefore, the results obtained here should find important practical utility in the performance optimization of a commercially viable disk MHD-generator system.