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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. Index Terms--Boundary-layer separation, disk MHD generator, enthalpy extraction (EE) ratio, flow behavior, generator performance, isentropic efficiency (IE).

Recent results of high-enthalpy extraction experiments with closed-cycle MHD disk generators are described. Power generation experiments were carried out with two types of facility: the shock tube facility with the Disk-IV generator and the FUJI-1 blow-down facility. In the shock tube experiments, the effect of channel shape on generator performance was studied using helium seeded with cesium as working fluid. A more divergent channel shape was effective in sustaining a high Hall field throughout the channel and achieving high generator performance even under the strong MHD interaction. High-enthalpy extraction of 27.3 percent was achieved. Furthermore, these experimental results agree well with the results of one-dimensional calculations. In the FUJI-1 blow-down experiments, the effect of stagnation gas pressure on performance was studied with a working gas of seeded argon. The highest enthalpy extraction ratio of 15.7 percent was achieved with the lower stagnation pressure of 0.46 MPa, whereas the largest output power of 516.7 kW and power density of 70 MW/[m.sup.3] were extracted with the nominal stagnation pressure of 0.6 MPa. This suggested the possibility of a part-load operation without significant degradation of generator performance by reducing stagnation pressure.

The shock-tunnel-based experiments and quasi-three-dimensional numerical simulations were used to determine the effect of a radio-frequency (rf) power application on the performance of a magnetohydrodynamic (MHD) electrical power generator. The results showed that a small amount of rf power assisted by preionization drastically changed the entire MHD power-generating system, considerably extended the MHD extraction length, and significantly improved isentropic efficiency.

It has been observed that the values of the magnetizing reactances in both d- and q-axis are reduced significantly from their corresponding unsaturated values as a result of nonlinearities introduced by saturation under both steady-state and transient operations. In the round rotor synchronous machine, q-axis magnetic circuit saturates appreciably more than that along the d-axis because of the presence of the rotor teeth. In the second section, a new method to calculate the q-axis saturation characteristic from the existing d-axis saturation characteristic has been presented. We have next calculated the saturated values of the d- and q-axis self magnetizing reactances and mutual cross magnetizing reactances between the two orthogonal axes under the steady-state operation. Finally, the effect of saturation, particularly the effect of q-axis saturation, on the power system transient stability has been presented. Index Terms--Cross-Saturation, q-axis saturation, saturated reactances, saturation, synchronous machine, transient stability.