Hiroshi Katsurayama

Experiment on Drag Enhancement for a Blunt Body with Electrodynamic Heat Shield

The electrodynamic heat-shield technique, which is known as a potential alternative to the conventional thermal protection system in a reentry flight, enables us to control directly a partially ionized plasma flow in a shock layer as a result of the interaction between the flow and a magnetic field applied around a reentry vehicle. The origin of the interaction is the Lorentz force generated by the magnetic field. As a result of the control, we can expect not only a shock-layer enhancement, which causes heat flux mitigation, but also a reaction force to the vehicle in which the magnetic field generator is mounted. Such a reaction force causes a drag enhancement for the vehicle. In the present study, we experimentally verify not only the drag enhancement but also the integrated Lorentz force, which is the main cause for the drag enhancement. This experimental verification is a direct corroboration of the interaction that is a basis of the electrodynamic heat-shield technique.

Numerical Analyses of Exhaust and Refill Processes of a Laser Pulse Jet

The exhaust-refill processes in a laser pulse jet with a conical nozzle are simulated using computational fluid dynamics to clarify the analytically unpredictable decreasing tendency of a momentum-coupling coefficient with an increasing nozzle apex angle. Because the exhaust-refill processes result from an adiabatically expanding blast wave after laser heating, a valid explosion source based on a measurement is used to drive the blast wave instead of a laser-absorption process. Results of computations show that processes that occur until the shock front of a blast wave reaches the nozzle exit are similar, irrespective of the nozzle apex angle. However, after the blast wave leaves the nozzle edge, the behavior of the rarefaction wave induced behind the shock wave depends greatly on the nozzle apex angle. In the case of small apex angles, successive refilling mechanisms with a vortex are activated by the prominently evolved rarefaction wave. In contrast, in the case of large apex angles, this mechanism disappears, due to the moderate evolution of the rarefaction wave. This difference creates a tendency of the momentum-coupling coefficient to decrease with the apex angle.

Numerical analyses on pressure wave propagation in repetitive pulse laser propulsion

Pressure wave propagation in a repetitive pulse air-breathing laser thruster flying at Mach 5 flow has been computed in order to clarify the behavior of a shock wave induced by focusing laser beams in supersonic flow, as well as to estimate the impulse acting on the thruster. As a result, the detailed process of shock reflection on the body and the mechanism for thrust generation have been analyzed. Moreover, the estimated coupling coefficient, which is the cumulative impulse per one pulse of laser energy, has been found to be fairly constant at a value of approximately 150 N • s/MJ, being independent of the laser energy. Results also reveal that the coupling coefficient is sensitive to the focus location.

Thermochemical nonequilibrium modeling of a low-power argon arcjet wind tunnel

Non-transferred low-power arcjet wind tunnels with pure argon working gas are widely used as inexpensive laboratory plasma sources to simulate a weakly ionized supersonic flow around an atmospheric entry vehicle. Many experiments using argon arcjet wind tunnels have been conducted, but their numerical modeling is not yet complete. We develop an axisymmetric Navier-Stokes model with thermochemical nonequilibrium and arc discharge that simulates the entire flow field in a steady-operating argon arcjet wind tunnel, which consists of the inside of the arcjet and its arc plume entering a rarefied vacuum chamber. The computational method we develop makes it possible to reproduce the arc column behavior far from thermochemical equilibrium in the low-voltage discharge mode typical of argon arcjets. Furthermore, the results reveal that the plasma characteristic of being far from thermal equilibrium, which is particular to argon, causes the arcjet to operate in the low-voltage mode and its arc plume to be completel...

Magnetoaerodynamic Force on a Magnetized Body in a Partially Ionized Flow

The magnetoaerodynamic force exerted on a magnetized model in a weakly ionized flow was investigated. In particular, the effects of the applied magnetic field’s orientation with respect to the model axis were examined by rotating a spherical permanent magnet installed in the nose of the model. The axial force increase due to the applied magnetic field is clearly influenced by the orientation of the applied magnetic field and takes on a maximum value when the line connecting the magnetic poles (magnetic pole line) is perpendicular to the incoming flow direction, whereas it takes on a minimum value when the magnetic pole line is moderately inclined against the incoming flow direction. Furthermore, the side force appears when the orientation of the applied magnetic field is apart from the incoming flow direction, whereas it disappears when the magnetic pole line is perpendicular to the incoming flow direction.

Magnetic-Field Configuration Effect on Aerodynamic Heating of a Magnetized Body

In this study, the aerodynamic heating rate of a magnetized model in a weakly ionized flow was investigated. The effects of the applied magnetic field and its orientation with respect to the model axis were investigated by rotating a spherical permanent magnet installed in the nose of the model. Contrary to simple theoretical predictions, when the magnetic poles are aligned along the incoming flow direction, the aerodynamic heating in the stagnation region is higher than that in the absence of amagneticfield and is slightly lower away from the stagnation region. In addition, it is clearly observed that the distribution of the heat flux is influenced by the orientation of the applied magnetic field. In particular, when the magnet poles are perpendicular to the incoming flow direction, the aerodynamic heating across the entire nose of the model is lower than that for an unmagnetized body.

Impact of the Lift Force by Electromagnetic Flow Control on the Reentry Trajectory

The effect of the lift force created by the tilted magnetic field on reentry flight trajectory was investigated by trajectory analyses. The results showed that when the lift-to-drag ratio of 0.1 was achieved by applying the magnetic field of 1 [T] both the reentry heating and the deceleration can be mitigated drastically. The effect of the additional mass for the electromagnetic system on the trajectory is also investigated. The results showed that the effect of the mass increase on the reentry flight environment can be compensated by increasing the magnetic field strength.

Fundamental Researches on Laser Powered Propulsion

An open-nozzle type air-breathing propulsion powered by a RP laser and a cavity type thermal thruster powered by a CW laser have been investigated at the university of Tokyo. The energy conversion from the laser pulse to the thrust work in RP laser propulsion has been estimated by plasma expansion measurement, CFD simulation, and engine cycle analysis. As for the CW laser thruster, energy balance in a thrust chamber has been evaluated by experiment and computation, and methods to improve the performance have been discussed. Dual focusing was tested as one example.

Laser Pulsejet with Beam Concentration by Multiple Reflections in a Sharp-Cone Nozzle

A sharp cone is employed as a nozzle for pulsed laser propulsion. A laser beam is concentrated by multiple reflections inside of the cone to generate plasma. Impulse measurements reveal that a large momentum-coupling coefficient, around 0.3 mNs/J, is achieved. By comparing the experimental and computational impulses, 15% of the laser pulse energy is found to be converted to the internal and kinetic energies of gas inside of the blast wave. This estimation of energy efficiency is supported by ray-tracing analysis of the cone and other experimental results of the energy efficiency. Moreover, the conical nozzle is found to be tolerant to optical misalignment.

Numerical Analysis on Nozzle Configuration and Thrust Performance of Laser Pulse-Jet

The relationship between the momentum-coupling coefficient C and the nozzle cone-angle of laser pulse-jets is investigated using Computational Fluid Dynamics. Temporal variations of thrust and pressure fields inside and outside conical nozzles are obtained, and computed C is compared with measured one. As a result, the computation well reproduces the measured C and its decreasing tendency with the nozzle cone-angle. The reason of this tendency is explained in relation to two-dimensional flow characteristics in its air-refresh process. In addition, it is suggested that the laser pulse width should be short enough that the laser-heated region can be smaller than the optimum nozzle size.