A study of the T-layer MHD generator/accelerator using nonequilibrium plasma

This study concentrates on understanding the gasdynamics of T-layer interaction in the MHD channel, and on predicting the performance potential of MHD devices (generator and accelerator) that use the T-layer principle. The effects of applying a nonequilibrium plasma without seed in the T-layer MHD device is evaluated. Argon is used as the working fluid. A one-dimensional unsteady model is developed to simulate the T-layer MHD process with a nonequilibrium plasma which is described by a two-temperature model. The unsteady model is coupled with a criterion for determining the onset of nonequilibrium plasma. The derived unsteady governing equations are solved numerically by a second-order high-resolution TVD (total variation diminishing) scheme. A quasi-steady model based on works of Vasilyev et al.^19,38,44 is included in this study to provide more support to the results obtained. Sample cases with typical operating conditions of the T-layer MHD generator as well as accelerator are examined. Reasonable consistency is seen between the results calculated by the two models. In the results, significant elevation of the electron temperature over the gas temperature is observed. The unsteady model is also verified by reported experimental results. When including the voltage drop due to the cold wall boundary, acceptable agreement is found between the calculated results and the experimental data with the exception in matching the peak value of current density. The processes in the MHD channel coupled with a formation section are simulated with single or with multiple T-layer(s) in the channel. The results show that when using multiple T-layers the performance increases only prior to the encounters between the T-layers and the wave perturbations caused by other T-layers. This interaction between T-layers influences the plasma properties inside the T-layers in an irregular way and subsequently causes fluctuations in the output and degrades performance of the devices. With a monatomic or molecular gas as the working medium, performance maps based on the quasi-steady model are constructed to provide a general view of the performance potential for the T-layer generator and accelerator.