Numerical simulation of discharge structures in Ar/Cs nonequilibrium plasma MHD generator
As reported in previous papers, the quasi-one-dimensional simulation code has come to predict almost satisfactorily the performance of the shock tube driven disk MHD generator using cesium seeded argon plasma as working fluid. However, the agreement between experimental and predicted performances was not so good on the conditions that the external load resistance was small, the seed fraction was high or the stagnation pressure was low. On these conditions, it was observed that ionization instabilities occur in the MHD channel. On the other hand, high-speed photographs of the nonequilibrium plasma discharge in the MHD generator were taken on several working conditions during the experiment. From these photographs, discharges were classified into almost three kinds of patterns. (a) A single strong luminous ring-type discharge near the nozzle exit for low seed fraction, (b) an almost uniform discharge inside the MHD channel for medium seed fraction, (c) multiple ring-type or spiral discharges in the MHD channel for high seed fraction. The structures of the discharge were sometimes two-dimensional especially for high seed fraction. Therefore, it may be impossible in this case to simulate them and to predict the performance precisely with one-dimensional simulation code. In the present study, two-dimensional (r-q) numerical simulations were made on the disk MHD power generation experiment (thermal input is about 1.5MW). The objectives were to develop a numerical simulator with high accuracy for the disk MHD generator and to explain some interesting phenomena concerned with nonequilibrium plasma discharges. The system of basic equations was solved mainly using CIP method. The calculation region was taken as that located between the throat to the inlet of the second (final) cathode. The main results are summarized as follows; (A) On the condition that the seed fraction was lower than the optimum value, it was succeeded to simulate numerically the single strong luminous ring-type discharge. The ring-type discharge was caused by the partial ionization of argon due to the rapid increase in the electron temperature in the nozzle. The pressure increase like a shock wave was also induced there. (B) On the condition that the seed fraction was near the optimum value, an almost uniform plasma was obtained in the simulation and in the experiment. (C) On the condition that seed fraction was higher than the optimum value, A similar structure of discharge to experimental one was obtained in the calculation due to an ionization instability (streamer) caused by the partial ionization of seeded cesium. (D) The performances of the generator such as enthalpy extraction can be predicted well with this simulation code.
- Research Organization:
- Tokyo Inst. of Technology (JP)
- OSTI ID:
- 20000318
- Resource Relation:
- Conference: 33rd Intersociety Energy Conversion Engineering Conference, Colorado Springs, CO (US), 08/02/1998--08/06/1998; Other Information: 1 CD-ROM. Operating system required: Windows 3.x; Windows95/NT; Macintosh; UNIX. All systems need 2X CD-ROM drive., PBD: 1998; Related Information: In: Proceedings of the 33. intersociety energy conversion engineering conference, by Anghaie, S. [ed.], [2800] pages.
- Country of Publication:
- United States
- Language:
- English
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