野中 聡

The density distribution in shock layer over a sphere is measured in a ballistic range by using finite fringe holographic interferometry. The measurement is made for a hemisphere of nose-radius of 15 mm, flight speed of 2.53 km/s, and initial pressure of 5,065 Pa. The obtained finite fringe interferogram is analyzed by Fourier transform techniques and an Abel deconvolution method to produce density maps. From the obtained density distribution, the density increase due to the real-gas effects was clearly recognized. The density profiles are compared with nonequilibrium calculation by using two-temperature model, and the numerical results well reproduce the density profiles. © 2000 by American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Shock standoff distance for a sphere is calculated to examine the behavior of the existing two-temperature model in the intermediate hypersonic flow regime. Calculations are carried out for three binary scaling parameter values, corresponding to nearly frozen, nonequilibrium, and nearly equilibrium flows, respectively. The obtained shock standoff distances are compared with the experimental data obtained in a ballistic range. It is shown that the two-temperature model reproduces the shock standoff distances in the intermediate hypersonic flows fairly well but tends to lose its accuracy where vibrational excitation occurs but chemical reactions are nearly frozen.

© 1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. The shock shapes over spheres, sharp-cones and double-cones are measured in a ballistic range in the intermediate hypersonic regime. The measurement is made in air for spheres with diameter of 14 and 30 mm, sharp-cones with half-angles of 30- and 45-degree, a double-cone with 25- and 65-degree half-angle, flight speeds between 2.43 and 3.85 km/s and ambient pressures between 600 and 10000 Pa. The flowfield is visualized by shadowgraph or schlieren method using a short-pulse Nd-YAG laser as the light source. The obtained shock shapes are compared with theoretical and calculated values, and the shock layer thickness are shown to vary due to the test conditions, demonstrating the effect of real-gas phenomena and angle of attack.

© 1999, American Institute of Aeronautics and Astronautics, Inc. Shock shapes for a sphere and a sharp-cone in intermediate hypersonic flow regime are calculated to examine the existing two-temperature thermo-chemical model. For sphere, calculations are carried out for two different flight velocities with a constant binary scaling parameter of 4.0×10-4 kg/m2. For sharp-cone, calculations are carried out for two different static pressure values at the flight velocity of about 3.0 km/s. The calculated shock layer thickness is compared with the corresponding experimental data obtained in a ballistic range. It is shown that the two-temperature model generally well reproduces the shock shapes over a sphere and a sharp-cone. However, the calculated shock layer thickness tends to be thinner than the experimental data, where the flowfield is chemically frozen and vibrationally highly excited.

© 1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Hypervelocity impact tests with bumper walled structure are conducted in a two stage light gas gun. The bumpers are made either of aluminum alloy, carbon/polyimide, flexible insulation + Al, 2.5D carbon/carbon + Al, fiber metal laminates, or ceramic. The impact velocity is about 4 km/sec. The debris cloud is visualized by the shadowgraph method or by using a multi-frame image converter camera. The damages to the main wall are compared among the bumper materials. The efficiency of the nonmetal bumper shielding is found to be superior to that of the metal bumper in both specific density and effectiveness protection.

© 1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. The experimental activities at Shock Wave Research Center of Tohoku University using a ballistic range are reviewed. First, the shock stand-off distance for a sphere and the shock shape over a sharp cone are measured in the hypersonic speed regime. These measurements are made for 30 mm diameter models, flight speeds between 2.5 and 4.0 km/sec and ambient pressure 4.2 and 76 mmHg. The flow field is visualized by the schlieren method using a short-pulse Nd-YAG laser as the light source. Shock stand-off distance and shock shape are shown to vary with the ambient pressure, demonstrating the effect of the chemical nonequilibrium. Secondly, hypervelocity impact tests are conducted for simulation of space debris impacts against a bumper shield. The bumpers are made of metal and nonmetal materials. The projectile made of high density polyethylene has a cylindrical shape of 14 mm diameter and 3.7 g in weight. The impact velocity is about 4 km/sec. The debris cloud is visualized by shadowgraph. The nonmetal bumper shields used in this study are more effective than the metal bumper in regard to both the bumper mass and defensive capacity.

© 1997, American Institute of Aeronautics and Astronautics, Inc. The shock Stand-Off distance for a sphere is measured in a ballistic range in the hypersonic speed regime. The measurement is made for spheres of diameter between 28 and 30 mm, flight speeds between 2.56 and 3.15 km/sec and ambient pressures between 4.2 and 76 Torr. The flow field is visualized by the schlieren method using a Short-Pulse Nd-YAG laser as (he light source. Shock Stand-Off distance is shown to vary with the ambient pressure, demonstrating the effect of the chemical nonequilibrium. The data produced in this experiment is compared with the results of the previous investigation, and a good agreement is found at overlapping flow conditions.