Modeling of plasma virtual shape control of ram/scramjet inlet and isolator

The paper explores a reverse energy bypass concept of ram/scramjet propulsion control by energy addition and extraction in the propulsion flowpath. Instead of variable geometry, the concept relies on virtual shapes created by plasma/magnetohydrodynamic (MHD) devices or by other methods (including plasma-controlled external combustion). An inherent advantage of the proposed plasma/MHD control system is its flexibility, fast response, and the absence of moving parts. The fixed geometry is optimized for Mach 7 flight. At Mach numbers below the design value, inlet performance can be controlled by energy addition, with the power supplied by an MHD generator placed downstream of the combustor. This concept is called the reverse energy bypass. In one scenario, the inlet flow spillage can be reduced by a virtual cowl - a heated region placed upstream of and slightly below the cowl. With an optimally located virtual cowl, calculations with conservative assumption regarding power transmission losses show that the reverse bypass can increase thrust by about 10% at Mach 6. In another scenario, distributed heating of the flow upstream of the inlet throat in the ramjet regime (Mach 4-6), with the heating rate of about 6.3-8.5% of the total enthalpy flux, can bring the throat Mach number close to one, thus making the isolator duct virtually unnecessary. Although the reverse bypass system with inlet heating would reduce thrust by about 16% at Mach 5, the performance penalty at the vehicle acceleration stage can be offset by the increased efficiency during cruise because of the absence of weight and cooling burdens, which would normally arise from using a long isolator duct.