Hirotaka Otsu

Influence of Hall Effect on Electrodynamic Heat Shield System for Reentry Vehicles

The influence of the Hall effect on the magnetic flow control to a reentry vehicle with a hemispherical nose and the imposed dipole magnetic field was investigated. For this purpose, a parametric study for the Hall parameter was conducted. The present result shows that the Hall effect drastically affects the electric potential distribution and electric current pattern inside the shock layer, depending on the vehicle surface conductivity, but it does not affect the current strength in the circumferential direction in the case of the insulating wall. As a result, the shock-standoff distance does not change, even if the Hall effect is significant when the vehicle surface is regarded as an insulating wall. The present parametric study clarified that this conclusion is applicable in a wide variety of the Hall parameter and enables us to get an insight of the mechanism behind the phenomenon. This conclusion suggests that, if the vehicle surface is regarded as an insulating wall, the magnetic flow control for the reentry vehicle will prove to still be a useful technology, even when the Hall effect is taken into account.

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.

Effective Test Time Evaluation in High-Enthalpy Expansion Tube

Flow characterization experiments of stagnation enthalpies up to 37 MJ/kg are carried out in the recently commissioned expansion tube facility. The features and the effective duration time of the test flowfield are determined not only from static and pitot pressures but also by observing the temporal variation of radiating emission from a shock layer around a spherical forebody. The thickness of the radiating layer matches well with the numerical results. The arrival time of the contact surface between the acceleration and test gases is better identified both as a decrease in the radiating layer thickness and from the emission spectroscopy. The useful test time is determined by integrating the mentioned measurements

Feasibility Study on the Flight Demonstration for a reentry vehicle with the Magnetic Flow Control System

In order to investigate the feasibility of the flight test for showing how effective the magnetic flow control system is for reentry vehicles we performed the trajectory analyses. As an initial flight condition, we prepared two different conditions; reentry flight from LEO and suborbital flight using a sounding rocket. For simplicity, a vehicle configuration is assumed to be a sphere with a radius of 20 [cm] and the magnetic dipole is placed at the center of the sphere. The magnetic field strength at the stagnation point was varied up to 2.0 [T]. Numerical results indicate that the flight performance improvement such as reduction in the maximum stagnation point heat flux was clearly observed in both flight conditions and, thus, the flight demonstration for the magnetic flow control system is evaluated to be feasible.

Numerical Study of the Electromagnetic Control of a Weakly Ionized Flow around a Blunt Body: Role of an Insulative Boundary in the Flow

The electromagnetic flow control was simulated using magnetohydrodynamic equations including the Hall effect to clarify the electromagnetic effects measured in an arcjet flow. The result showed that the combined effect of the Hall effect and an insulative boundary in the flow activates the electromagnetic flow control: an ideal uniform ionized flow without any insulative boundary in the flow was found to be unsuitable to investigate the electromagnetic flow control experimentally. In addition, the present study computes the flow with an artificial insulative plume boundary to imitate the non-uniformity of the experimental flow. As a result, the measured drag increase was reproduced if an artificial insulative boundary is set to the location identical to the plume radius estimated on the basis of the measurements. Consequently, the measured drag increase in the arcjet flow results from the plume boundary serving as an insulative boundary.

Electron Density Measurements Behind Strong Shock Waves by H-ß Profile Matching

Emission spectroscopy was performed in a free-piston double-diaphragm shock tube to measure the electron density behind a strong shock wave, using nitrogen as the test gas. Time-frozen spectra from behind the shock wave were taken by an image-intensie ed charge-coupled device camera with a gate width of 100 ns. The laser schlieren diagnostics was used to detect the shock arrival and to correlate observed spectra with the distance from theshock front accurately. Theelectron density wasmeasured by meansof a lineproe le matching technique, using the H-¯ line broadened by the Stark effect. Using this measurement system, the electron density distribution was obtained with a high spatial resolution of §0:6 mm at a shock velocity of 12 km/s. Experimental results show that, especially at high shock velocities, the measured electron density increases more quickly behind the shock front than predicted by the thermal and chemical nonequilibrium models widely used. Several drawbacks in the conventional ionization model at high shock velocities are pointed out.

Radiative Heating Analysis around the MUSES-C Reentry Capsule at a Superorbital Speed

The thermally and chemically nonequilibrium hypersonic flow around the MUSES-C reentry capsule was analyzed. Radiation analysis all around the capsule is also performed. The typical reentry speed is 11.6km/s at the altitude of 64km. In such a high velocity reentry condition, the vibrational-electronic temperature and the radiative heatflux, which is strongly dependent on the vibrational-electronic temperature, are very sensitive to the models for the relaxation processes. Especially, the two mechanisms, which are the relaxation process for electron and the electron impact ionization, are dominant.

Model and magnetic configuration effect on shock layer enhancement by an applied magnetic field

The combined effect of the model configuration and the magnetic field configuration on shock layer enhancement phenomena attributable to the applied magnetic field was investigated experimentally. For this study, two test models were used. One was a flat-faced model with a cylindrical permanent magnet. The other was a spherical blunt model with a spherical permanent magnet. The translational temperature distributions ahead of the two test models (i.e., the shock layer region) were measured using laser absorption spectroscopy. Comparison of the results obtained using the two test model cases showed that the shock layer enhancement caused by the applied magnetic field was greater for the spherical blunt model than for the flat-faced model. That experimental result qualitatively agrees with the computational fluid dynamics results, which suggest that the combined effect of the magnetic configuration and stream line (i.e., the model configuration) play key roles in shock layer enhancement phenomena.

Model surface conductivity effect for the electromagnetic heat shield in re-entry flight

Effects of model surface conductivity on shock layer enhancement by an applied magnetic field in weakly ionized supersonic plasma flow with a large Hall parameter (β∼300) was investigated experimentally. The shock layer structures of test models of two kinds were measured using laser absorption spectroscopy, in the large Hall parameter situation. One was an insulated model; the other was a conductive spherical blunt model. The shock layer enhancement phenomenon by the applied magnetic field was more pronounced for the insulated model than for the conductive model. This tendency agrees with the computational fluid dynamics result, at least qualitatively.

Numerical Investigation of High-Enthalpy Flows Generated by Expansion Tube

We have investigated by numerical simulation the hypersonic and high-enthalpy flows around a reentry body, which Sasoh et al. examined experimentally in an expansion tube facility. For the experiment, the evaluation of the timing at which the test flow is attained and the freestream condition ofthe test flow are the most crucial issues. Therefore, it was necessary to validate these issues in another way, rather than the simple estimation by Sasoh et al. based on the pressure and spectral emission measurements. Thus, the experimental result was intensively investigated compared to the numerical result based on the experimentally determined freestream condition