A fluid-structure coupled computation code has been developed and applied to a panel flutter problem. The flutter velocities and the amplitudes of limit cycle oscillations obtained using the present method agree well with those of Dowell. It is found that the boundary layer over the panel can suppress flutter particularly in the Mach number region between 1.2 and 1.35, the effect of which increases with viscosity. In a 3D problem, good agreement was obtained between computation and experiment.
In the ram/scramjet engines, transition of the combustion mode from subsonic one to supersonic one is very important in their performance and operation. The subsonic mode combustion occurs behind a pseudo-shock wave (PSW) in a isolator, while the PSW disappears in the supersonic mode. The mode transition sometimes shows hysteresis feature caused by strong interaction among shock waves, mixing and combustion. It is necessary to understand the mechanism of this interaction for prediction of the scramjet engine performance. In our previous study, the PSW was produced by mechanically controlling back pressure of a duct, and its effect on the mixing was investigated. In the present study, the PSW was produced by hot gas injection from a N2 or H2/N2 plasma torch in a Mach 2.3 airstream. The distributions of gas composition, pitot pressure, and stagnation temperature at the exit of the test section as well as the wall pressure distribution were measured to investigate the mechanism of PSW formation by heat addition and its influence to the mixing.
This study investigated the thermo-elastic properties and microscopic ply cracking behaviors in carbon fiber reinforced nanotube-dispersed epoxy laminates. The nanocomposite laminates used in this study consisted of traditional carbon fibers and epoxy resin filled with cup-stacked carbon nanotubes (CSCNTs). Thermo-mechanical properties of unidirectional nanocomposite laminates were evaluated, and quasi-static and fatigue tension tests of cross-ply laminates were carried out in order to observe the damage accumulation behaviors of matrix cracks. Clear retardation of matrix crack onset and accumulation was found in composite laminates with CSCNT compared to those without CSCNT. Fracture toughness associated with matrix cracking was evaluated based on the analytical model using the experimental results. It was concluded that the dispersion of CSCNT resulted in fracture toughness improvement and residual thermal strain decrease, and specifically, the former was the main contribution to the retardation of matrix crack formation.
Specific impulse and burning rate characteristics are the important properties for the propellant design. Because of the requirements for the preparation of ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB) composite propellant, there is an upper limit content, φ of AP contained propellant. Specific impulse and burning rate increase with increasing the AP content. The specific impulse, Ispφ and the burning rate, rφ of the propellant prepared at φ, rφ are the highest values of the propellant prepared with AP used as an oxidizer. It is necessary for the propellant design to estimate φ, Ispφ and rφ. The φ, Ispφ and rφ are closely associated with the specific surface area, Swp measured by air-permeability method. Therefore, these values are estimated with Swp. A process for the design of AP/HTPB composite propellant would be proposed in this study.
Microwave discharge Hall thruster can be operated by two operating modes. The first one is “no microwave launching” mode, thus having the thruster operating as single-stage type. The other mode is “microwave launching” mode, thus having the thruster operating as double-stage type. In order to examine the influence of microwave launching mode upon the plasma condition inside the acceleration channel, as well as the relationships between thruster performance and acceleration channel length, single-probe measurements and ion beam energy diagnostics in the plume were carried out. Single-probe measurements revealed the existence of dense plasma and high electron temperature region in the acceleration channel upstream due to the heating of the electrons by microwave. The variation in the discharge current characteristic due to the difference in acceleration channel length was not significant. As for discharge current, double-stage operation always results in a lower value compared to the value at the single-stage operation. Ion beam current was always higher at double-stage operation compared to the value at single-stage operation. Voltage utilization efficiency has improved as the channel length became short with microwave launching.
A method is presented for designing the thermal control system for 50kg-class micro-satellite using a genetic algorithm. Replacing the thermal control system into a heat transfer model, i.e. a thermal network model, the problem is treated as an optimization problem to find suitable combinations of adapted thermal control elements under admissible function keeping the controlled temperature within a selected band width. Admissible function used herein consists of two parameters; the one is a slope of temperature variation and the second is an amplitude of temperature variation during on orbital motion of satellite. To demonstrate the validity of the proposed method, the method is applied to two examples for the thermal control system design of a 50kg-class micro-satellite, tentatively called “SOHLA-1”, under development.
The flow field in the cross-flow separation region of an axisymmetric paraboloid at angles of attack of 40 and 50deg has been investigated experimentally by hot wire anemometer for the Reynolds numbers of 1.8×104 and 7.5×104 referred to the base diameter. The propagating process of turbulence in the separated vortices and the switching phenomenon of the flow have been clarified for each Reynolds number and angle of attack. The behavior of each vortex is estimated by calculating the skewness distribution of the velocity fluctuation. The difference of the process of vortex mergence for angles of attack has been identified.