Modeling plasma and MHD effects in hypersonic propulsion flowpath

A concept of ram/scramjet propulsion control by energy addition and extraction in the propulsion flowpath is analyzed. Instead of variable geometry, the concept relies on virtual shapes created by plasma/MHD devices or by other methods (including plasma-controlled combustion). An inherent advantage of the proposed plasma/MHD control system is its flexibility, fast response, and the absence of moving parts. At Mach numbers higher than the design value, an MHD generator placed at the first compression ramp and using ionization by electron beams can restore the shock-on-lip condition, while operating in self-powered regime. 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 Virtual Cowl - a heated region placed upstream of the cowl and slightly below it. With 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 1, thus making the isolator duct virtually unnecessary. In this scenario, the performance penalty at the vehicle acceleration stage can be offset by the increased efficiency during the cruise due to the absence of weight and cooling burden normally caused by the long isolator duct. The paper also describes the development of a modular computational code that would allow users to analyze all the important aspects of plasma/MHD processes in the propulsion flowpath of hypersonic vehicles and to evaluate the performance in terms of specific impulse and thrust. Problems in quasi-one-dimensional modeling of devices with inherently non-onedimensional flow are discussed, and a method of solving these problems is proposed.