Performance of closed cycle disk MHD generator with inlet fluctuation of seed fraction

The influence of inlet seed fraction fluctuations on the performance of closed-cycle MHD disk power generators is investigated using time-dependent two-dimensional numerical simulation. Here, the nonuniformity scale of the seed fraction, as induced by inlet fluctuations, is assumed to be comparable to the length of the channel or smaller. It is confirmed that inlet fluctuation of the seed fraction can cause instability in nonequilibrium plasma and deteriorate the performance of the generator. As the amplitude of the inlet fluctuation increases, the amplitude of the enthalpy extraction ratio fluctuation becomes enlarged and the mean value is decreased. Furthermore, the amplitude of the enthalpy extraction ratio fluctuation grows larger when the frequency of the inlet fluctuation approaches 8-10 kHz. Although inlet fluctuations induce oscillations in both plasma and flow-field parameters, they display different characteristics at higher frequencies. That is, fluctuation of the former is kept approximately constant with increasing frequency whereas the latter is weakened. This behavior can be attributed to the inertia of the flow field. For pulse-like random inlet fluctuations with high dominant frequency, the fluid field does not have adequate time to respond to variations in seed fraction. The resulting dominant frequency in the flow field is 4-6 kHz. The dominant frequency for the output power is in the same range as the flow field, and these frequencies can be related to the residence time of the working fluid in the channel.