Motoo Ishikawa

Influences of electrical conductivity of wall on magnetohydrodynamic control of aerodynamic heating

Influences of the electrical conductivity of the wall of a space vehicle on the control of the aerodynamic heating in Earth-reentry flight by applying the magnetic field are numerically examined using an axisymmetric two-dimensional (r-z) thermochemical nonequilibrium magnetohydrodynamic computational fluid dynamics code. Numerical results show that when the wall of an axisymmetric blunt body is assumed to be an insulating wall, applying a dipole-type magnetic field with r and z components pushes the bow shock wave away from the blunt body and reduces the aerodynamic heating. On the other hand, when the wall is assumed to be a conducting wall, the aerodynamic heating cannot be reduced by applying the magnetic field. This is because the strong Hall electric field on the r-z plane cannot be obtained in the case of the conducting wall, so that the large electric current density in the azimuthal direction cannot be obtained and the shock wave cannot be pushed away from the blunt body.

Numerical Simulation of control of plasma flow with magnetic field for thermal protection in Earth reentry flight

The present numerical study examines the possibility and usefulness of the control of weakly ionized plasma flow ahead of a space vehicle by means of the magnetic field for thermal protection in earth reentry flight under the flight conditions at the altitudes from about 72 to 48 km along the real earth reentry trajectory of the blunt body OREX, which was used for an earth reentry experiment in 1994. Numerical results show that the aerodynamic heating can be reduced by applying the magnetic field at the altitude above about 55 km where the weakly ionized plasma is produced behind the bow shock wave, and also that the reduction amount of the aerodynamic heating by applying the magnetic field becomes larger with increasing the altitude. At the altitude of about 60 km, where the aerodynamic heating had the peak value in the OREX experiment, the wall heat flux at the stagnation point and the total aerodynamic heating over the wall surface with applying the magnetic field of about 0.5 T are, respectively, 85% and 67% of their values obtained without applying the magnetic field.

Numerical Analysis of Reentry Trajectory Coupled with Magnetohydrodynamics Flow Control

Effects of the magnetohydrodynamics flow control on Earth reentry flight characteristics are examined by a coupled numerical analysis of the reentry flight trajectory and the magnetohydrodynamics flows with thermochemical reactions. Initial flightaltitude andvelocity ofabluntbody withanoseradius of1.35 mare 75.3km and7:2 km=s,respectively.Numericalresultsshowthatathighaltitudessuchasabout75km,themainfactorofthe mitigation of wall heat flux by the magnetohydrodynamics flow control is the increase of the thickness of the shock layer by applying the magnetic field. At low altitudes such as about 55 km, on the other hand, the main factor of its mitigation isthedecrease of flight velocitydueto thechangeof flighttrajectory byapplyingthe magnetic field.It can also befound from a rough estimation thatabout 75%of its mitigation amount at the altitude of about 60 km, where the aerodynamic heating is severest, is attributed to the decrease of flight velocity by applying the magnetic field.

Numerical Analysis of Reentry Trajectory Coupled with MHD Flow Control

Effects of the MHD flow control on the reentry trajectory and the aerodynamic heating are examined by a coupled numerical analysis of the reentry flight trajectory and the MHD flows with thermochemical reactions. Initial flight conditions of a reentry blunt body with the nose radius of 1.35 m are the flight altitude of 75.3 km and the flight velocity of 7.2 km/s. The coupled numerical analysis is terminated when the blunt body reaches the altitude of 45 km. Numerical results show that at high altitude such as about 75 km, the main factor of the mitigation of wall heat flux by the MHD flow control is the enhancement of shock layer caused by applying the magnetic field. At low altitude like about 55 km, on the other hand, the main factor of its mitigation is the decrease of flight velocity due to the change of flight trajectory by applying the magnetic field. The peak value of wall heat flux at the stagnation point in the reentry flight with applying the magnetic field of about 0.5 T is mitigated to about 73 % of the peak value obtained without applying the magnetic field, and the decrease of flight velocity contributes to about 75 % of the whole mitigation.

Axi-symmetrization of radiation pattern and two wave heating of fundamental ECRH in GAMMA 10

Abstract In GAMMA 10, the radiation pattern of a heating wave of fundamental ECRH for potential formation was not axi-symmetric but vertically elongated on the resonance surface. The non-axisymmetric radiation pattern caused a non-axisymmetric potential profile and likely induced a radial loss. Then, the radiation pattern has been axi-symmetrized. Accordingly, an almost axi-symmetric potential profile has been obtained and a large density increase during ECRH has been observed in the central cell. This implies that radial losses associated with ECRH have been substantially reduced. A new antenna has recently been installed for additional plug electron heating (second ECRH). With this antenna, a larger power and/or a longer pulse width have become available. In a most recent experiment, we have succeeded in axial plugging with a duration up to 0.15 s by sequential use of the usual ECRH and the second ECRH. Moreover, there is an indication that the second ECRH is more desirable for further reduction of the radial loss.

Effects of induced magnetic field on large scale pulsed MHD generator with two phase flow

A large pulsed MHD generator “SAKHALIN” was constructed in Russia (the former Soviet-Union) and operated with solid fuels. The “SAKHALIN” with the channel length of 4.5 m could demonstrate the electric power output of 510 MW. The effects of induced magnetic field and two phase flow on the shock wave within the “SAKHALIN” generator have been studied by time dependent, one dimensional analyses. It has been shown that the magnetic Reynolds number is about 0.58 for Run No. 1, and the induced magnetic flux density is about 20% at the entrance and exit of the MHD channel. The shock wave becomes stronger when the induced magnetic field is taken into account, when the operation voltage becomes low. The working gas plasma contains about 40% of liquid particles (Al2O3) in weight, and the present analysis treats the liquid particles as another gas. In the case of mono-phase flow, the sharp shock wave is induced when the load voltage becomes small such as 500 V with larger Lorentz force, whereas in the case of two phase flow, the shock wave becomes less sharp because of the interaction with liquid particles.

Loss mechanisms of travelling wave direct energy converters for D-3He FRC fusion reactors

Abstract Loss mechanisms of TWDEC for a D-3He fuelled FRC fusion reactor are studied with numerical analysis. (1) The self-excitation of a travelling wave has been attained with external electric circuits, which shows the conversion efficiency is about 70–73%. (2) Three-dimensional behavior has been studied by axisymmetric approximation, showing that the loss related to the radial non-uniformity effect without collision with grids is about 5%. (3) The loss related to the collision with grids is the most important, being about 11%. (4) Effects of secondary electrons produced by the collision with the grids are rather small and subrings can suppress the effects of secondary electrons. (5) The loss related to leaked 3.6 MeV α particles is about 45–60% of the total energy of leaked α particles. (6) The gross efficiency of TWDEC is estimated to be over 60%.

Numerical Analysis of Effects of Liquid Particles on Plasmadynamics in a Large-Scale Pulsed MHD Generator

The effects of the Al2O3 liquid particles on the plasmadynamics and the generator performance of a large-scale pulsed MHD generator “Sakhalin”, operated with a solid propellant and an MHD channel of 4.5m, having demonstrated the electric power output of 510MW, are numerically investigated by using the time-dependent two-dimensional analyses with the assumption of a two-phase flow. The Harten-Yee upwind TVD scheme is implemented for gas-phase equations, while the Galerkin finite element method is used to obtain the electrodynamical distributions. The liquid-phase is treated as a particle. For the experimental channel voltage of 2550V, in both cases of the particle diameter of m µ 15 and m µ 5 , the core flow experiences a smooth deceleration and the gasdynamical and electrodynamical distributions become almost symmetric in the Faraday direction. For the channel voltage of 1400V, in both cases of the particle diameter, a strong MHD interaction induces a boundary-layer separation in the MHD channel. The boundary-layer separation becomes very large because the liquid particles can follow the behavior of gas-phase in the case of the particle diameter of m µ 5 , while the growth of the boundary-layer separation is restricted because the liquid particles transfer the momentum into the separation region in the case of the particle diameter of m µ 15 . The electrical loss near the anode is quite large in the case of the particle diameter of m µ 5 , while it becomes much smaller in the case of the particle diameter of m µ 15 .

Prediction of Generator Performance and Aerodynamic Heating of Reentry Vehicle Equipped with On-board Surface Hall Type MHD Generator

The generator performance and the aerodynamic heating of a reentry body equipped with an on-board surface MHD power generator are numerically examined with different anode electrode configurations (shape and position) when the position and the shape of a cathode electrode are fixed. An axisymmetric two-dimensional body with a nose radius of 1.35 m is assumed to be equipped with a pair of the anode and the cathode electrodes on the wall surface, and also the anode electrode is placed to the stagnation point side and the cathode electrode is placed to the shoulder side. The flight velocity is about 5.6 km/s, the flight altitude is about 60 km, and the maximum value of an applied dipole magnetic field is 0.5 T. Numerical results demonstrate that the on-board surface Hall type MHD power generator can effectively mitigate the wall heat flux at the stagnation point as well as extract the electric power output exceeding one megawatt, if a ring-shaped anode electrode is placed away from the stagnation point. On the other hand, if a bowl shaped anode electrode is placed to cover a wide wall surface including the stagnation point, the wall heat flux at the stagnation point cannot be effectively mitigated by the MHD interaction although the electrical output power exceeding one megawatt can be obtained. This is because the bowl shaped anode electrode reduces the Hall electric field in a wide region around the stagnation point.

Effects of installed system dumping resistors on stability of open cycle disk type MHD generator connected to power transmission line

Abstract This study is performed as part of the wide research on large scale coal fired MHD generation systems. Faults in the power transmission line give remarkable fluctuations to the MHD generator and to the transmission network. Then, it is required to take countermeasures for stable operation of the generation system. The fluctuations do not converge to a stable state after cutting off the fault line in the transmission line because the commutation failure occurs in the inverter system after the line faults. The effects of installed system dumping resistors (SDR) on the stability of an open cycle disk type MHD generator connected to power transmission lines are numerically studied. Usually the AC SDR is installed in the AC primary grid of the transmission line for system stability. The SDR is used to absorb the output energy of the synchronous generator and to get stability of the power transmission system when faults occur in the transmission line. In this paper, we propose to install the SDR in the DC lines between the MHD generator and the primary side of connected line commutated inverters. We show that the SDR is effective for system stability by a time dependent numerical analysis. This study makes it clear that switching on the applied SDR using the thyristor switches in addition to cutting off the faulted transmission lines is effective to remove the fluctuations of the MHD generation system.