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This Defense Intelligence Reference Document from the Defense Intelligence Agency, dated 21 November 2010, was produced in FY 2010 under the Advanced Aerospace Weapons System Applications (AAWSA) Program. It reviews propulsion concepts that use plasmas and magnetohydrodynamics. It finds the Ajax MHD energy bypass concept meaningless below Mach 12 but calls a reverse energy bypass with a Virtual Cowl potentially practical. It also predicts that electric propulsion will become standard for spacecraft.
UNCLASSIFIED/ ,'P81t 8PPU!llltt tl!!II!! 8HL"i' Chapter 2: Aeronautical Applications - Concepts and System Issues In this section we will review the following issues and concepts: • Basic principles and problems of MHD propulsion, power generation, and flow control. • MHD inlet control. • MHD power generation in scramjet flowpath. • Plasma-generated virtual surfaces for drag reduction, steering, and virtual cowl. • MHD energy bypass: the Ajax concept. • The reverse energy bypass concept. • MHD power generation and aerodynamic control for reentry vehicles. BASIC PRINCIPLES OF MAGNETOHYDRODYNAMICS AND REQUIREMENTS FOR MHD PERFORMANCE The basic principles of magnetohydrodynamics (MHD) are understood very well. When an electrically conducting fluid crosses magnetic field lines, an electromotive force (Faraday e.m.f., equal to the product of flow velocity u and the strength of magnetic field B, uB, multiplied by the channel width) is induced across the fluid and the B field. If then a pair of electrodes is positioned on either side of the fluid flow and connected via a ballast resistor on the outside, an electric current will be induced in the circuit, and power will be generated on the external load. This electric power will represent partial conversion of the flow enthalpy (consisting of thermal and kinetic energy of the flow) into electricity. At the same time, the current flowing through the finite-conductivity fluid will produce Joule heatinga of the fluid that will increase both static temperature and entropy of the fluid. The ratio of the extracted electrical power to the Joule dissipation rate is determined by the ratio of the load resistance to the sum of load and fluid resistances; this ratio is called the "load factor," k, O<k<l. The current (current density j) induced in the fluid, being normal to both the magnetic field B and the flow direction, results in the body force per unit volume equal to jxB and directed against the flow. This body force, commonly called the "Lorentz force" (it should be properly called the ampere force or the ponderomotive force), is directed against the flow in MHD generators, acting to slow the flow down and reduce its total energy, which is in line with the electricity extraction. a Joule heating. given hy the expression, Q=1 2Rt, (Q is the heat generated hy a conqant current, I. flowing through a conductor of electrical resistance, R, for a time, t), i~ the process hy which the pa~~age of an electric current through a conductor relea~e~ heat If current, resi~tance. and time are expressed in amperes. uhms, and ~eeond~ respcctivdy. the unit uf Qi~ the _joule. The incrca~e in the kinetic ur vibratiunal collisiunal energy uf the iun~ and electrons manifests itself a~ heat and a rise in the temperature of the conductur. Rather than a wire. the conductur in this applicatiun i~ an ioniLcd f1uid. 11 UNCLASSIFIED/FQI!. QFFllil,roL WliE a,1Llit'
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 32 pages are in the text index: search them above, or from the library's search.