Annular MHD Physics for Turbojet Energy Bypass

The use of annular Hall type MHD generator/accelerator ducts for turbojet energy bypass is evaluated assuming weakly ionized flows obtained from pulsed nanosecond discharges. The equations for a 1-D, axisymmetric MHD generator/accelerator are derived and numerically integrated to determine the generator/accelerator performance characteristics. The concept offers a shockless means of interacting with high speed inlet flows and potentially offers variable inlet geometry performance without the complexity of moving parts simply by varying the generator loading parameter. The cycle analysis conducted iteratively with a spike inlet and turbojet flying at M=7 at 30 km altitude is estimated to have a positive thrust per unit mass flow of 185 N-s/kg. The turbojet allowable combustor temperature is set at an aggressive 2200 o K. The annular MHD Hall generator/accelerator is L=3 meters in length with a Br=5 Tesla magnetic field and a conductivity of =5 mho/m for the generator and =1.0 mho/m for the accelerator. The calculated isentropic efficiency for the generator is sg=84% at an enthalpy extraction ratio, Ng=0.63. The calculated isentropic efficiency for the accelerator is sa=81% at an enthalpy addition ratio, Na=0.62. An assessment of the ionization fraction necessary to achieve a conductivity of =1.0 mho/m is ne/n=1.90x10 -6 , and for =5.0 mho/m is ne/n=9.52x10 -6