Comparative Analysis of MHD and Plasma Methods of Scramjet Inlet Control
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abstract
The paper is devoted to analysis of magnetohydrodynamic (MHD) control of forebody flow compression, shock incidence, and air mass capture increase in scramjet inlets for vehicles that would fly at Mach 5-10. Due to the low static temperature, nonequilibrium electrical conductivity is created by electron beams injected into the gas along magnetic field lines. Two -dimensional inviscid steady-state flow equations are solved jointly with equations describing electron beam-induced ionization profiles, plasma kinetics, and MHD equations. Several scenarios are considered, based in part on earlier work by the present authors. The scenario with an on-ramp MHD accelerator that should increase mass capture at Mach numbers lower than the design value has only disadvantages, since the MHD device consumes high power, reduces total pressure, and actually decreases mass capture due to Joule heating and thermal expansion of the gas. A modest increase in mass capture can in principle be accomplished in a Faraday MHD generator mode, if the magnetic field has components both parallel and orthogonal to the flow. However, this scenario involves very large volumes of strong magnetic fields, and the mass capture increase is due mostly to a nonuniform gas heating. In a new "virtual cowl" scenario, a localized off-body energy addition is used to increase mass capture at Mach numbers lower than the design value, while also even increasing total pressure at the inlet. The principal focus of this paper is on inlet control at flight Mach higher than the design value. The shocks that would otherwise enter the inlet can be moved back to the cowl lip by placing an MHD generator at one of the compression ramps. Calculations and qualitative arguments show that the best performance of such a device (minimal losses of total pressure) is achieved with a very short MHD region in conjunction with high-current ionizing electron beam; the MHD region should be placed as far upstream (close to the vehicle nose) as possible. An MHD energy bypass scenario with on-ramp MHD generator for inlet control is briefly discussed. 2003 by the authors.
