MHD Generator Performance Investigation Of Hypersonic

The fundamental idea of MHD energy bypass is to use MHD energy conversion processes toextract and bypass a portion of the intake kinetic energy around the burner. It is possible to increasethe freestream Mach number for which the flow remains low Mach number and throughout theburner, and the ramjet mode can be sustained to much higher flight Mach numbers. In this scheme, theinlet air must be ionized and have high electrical conductivity to attain effective MHD interaction inthe generator. In this thesis, the flow characteristics and chemical nonequilibrium ionization in theMHD generator under magnetic field are simulated numerically.First of all, three dimensional MHD five-equation model associated with low magnetic Reynoldsassumption was used to simulate the flow phenomenon for a rectangular Faraday type MHD generatorwith segmented electrode, and the effects of load factors, intensity of magnetic field and the widthof the electrodes on the performance of the generator were investigated. The results showed that theelectrical power density reached maximum when the loading factor was0.5, and with the load factorincreases the slowing capacity of the generator was reduced. At the magnetic field strength of8T,electrical conductivity was20mho/m,500mm length of the generator could reduced the Mach numberfrom6to3below, keep the temperature below800K, and power generation could reach the amount ofmegawatt-scale of per cubic meter of the duct.Secondly, in order to comprehend the performance of hypersonic cold-air MHD powergenerators with ionization by electron beams, the flow phenomena of a rectangular Faraday typeMHD generator with segmented electrode were simulated using the three dimensional MHDfive-equation model associated with low magnetic Reynolds assumption and a simple model ofbeam-generated ionization. The effects of power spent on ionization on the results of ionization wasinvestigated，drawing the number density of electrons and electrical conductivity formed by theionization under different ionization spent. The results showed that electron beams were capable ofgenerating an adequate conductivity in cold air.At last, the performances of MHD generator under different power spent on ionization isinvestigated numerically. When the loading factor is0.5, electrical efficiency is substantiallymaintained at between0.5-0.6, and the intensity of magnetic field has no effect on electrical efficiency.When power spent on ionization is0.06(MW/m3),0.6(MW/m3),6(MW/m3),30(MW/m3), respectively,the conductivity σ(mho/m) is0.28、0.9、3、7、27, respectively.The energy extraction rate is of26%, close to the optimal performance of the generator, corresponding the intensity of magnetic field of10T and power spent on ionization was30(MW/m3).