AAWSAP DIRD, MHD Air Breathing Propulsion and Power for Aerospace Applications, November 2010

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owl lip
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treamline
Figure 9. Schematic of the Virtual Cowl Concept. Plasma-generated heated region
upstream of the cowl lip deflects the flow and scoops more air into the inlet.
Analysis of the reverse energy bypass involving MHD generator downstream of
the scramjet combustor and an optimized virtual cowl revealed that, although
enthalpy extraction and entropy production in the MHD generator substantially
reduce the thrust, the combined system with virtual cowl can actually increase
thrust by as much as 20-30%.35, 36
From the system standpoint, this concept, with all its associated weight and
complexity, should be compared with that involving a movable (variable
geometry) cowl that is associated with a heavy and complex electrohydraulic
system and also requires power. An attractive feature of the reverse bypass
concept that might make it a winner is its multifunctional nature. Indeed, MHD
power generation downstream of the combustor can be an attractive power­
production option for hypersonic vehicles. Alternatives (batteries, fuel cells, and
the like) are not very competitive for generation of large amounts (hundreds of
kW to 1-10 MW) of power onboard. Thus, if an MHD generator in the propulsion
flowpath is accepted as the power source, its operation in conjunction with a
virtual cowl that significantly increases thrust in off-design conditions, and also
enables aerodynamic control and maneuvering, would become quite practical.
Note also that if another source of high (MW-scale) power, such as a nuclear
reactor, is onboard, its use for virtual cowl, drag reduction, and aerodynamic
control would be straightforward and would greatly increase performance of the
hypersonic vehicle .
MHD APPLICATIONS TO REENTRY AND NEAR-ORBITAL FLIGHT
We now turn to MHD application to reentry and near-orbital flight. Due to the
high velocities and enthalpies involved, the gas temperature in shock and
boundary layers is very high, from several thousand to 10,000-20,000K. At
these temperatures, thermal ionization is very substantial, and at the low end of
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