As a research to develop a SCRAM-jet engine is actively conducted, a necessity to produce a high-enthalpy flow in a laboratory is increasing. In order to develop the SCRAM-jet engine, stabilized combustion in a supersonic flow-field should be attained, in which a duration time of flow is extremely short. Therefore, a mixing process of breathed air and fuel, which is injected into supersonic flow-fields is one of the most important problem. Since, the flow inside SCRAM-jet engine has high-enthalpy, an experimental facility is required to produce such high-enthalpy flow-field. In this study, a detonation-driven shock tunnel was built and was used to produce high-enthalpy flow. At first, a performance of this facility was investigated in order to obtain a Tayloring condition. Furthermore, SCRAM-jet combustor model equipped backward-facing step was installed at test section and flow-fields were visualized using color-schlieren technique. The fuel was injected perpendicular to the flow of Mach number three behind step. The height of backward-facing step and injection pressure were changed to investigate effects of the step on a mixing characteristic between air and fuel. The schlieren photograph and pressure histories show that the fuel was ignited behind step and the height of step is important factor to ignite a fuel in a supersonic flow-field.
The active limp joint was developed for the purpose of the joint for space robots from which good compliant nature is obtained to pulling in by the attaching mechanism in on-orbit assembly work. The contact work in on-orbit assembly work was analyzed, and joint active limp control was proposed as a force control system which realizes compliant action. Moreover, the small cable lap mechanism of the torque sensor of high stiffness and disturbance torque was developed. The space robot joint mechanism which these are built in was developed, and it verified that forcing for the object by application of fine joint torque sensor and joint compliance control could be performed by characteristic testing. Furthermore, it verified that good compliant action was realizable to pulling-in action by joint active limp control. Thus, the joint mechanism and control system suitable for the next-generation space robot arm which does on-orbit assembly work were developed.
In this study, biaxial tensile tests of cruciform specimens with open hole were conducted for evaluating the strength of the coated plain weave fabrics composed of high specific tensile strength fibers. In addition to the biaxial tensile tests, uniaxial tensile tests of strip specimens were also carried out to obtain uniaxial fundamental properties of the fabrics. As the results of the biaxial and uniaxial tensile tests, open hole tensile strength of the fabric under biaxial loadings is approximately equal to the strength under uniaxial load irrespective of biaxial load ratio, and warp directional strip specimens exhibit higher strength than that of weft directional specimens in spite of the same densities of yarns in both directions. Experimental results exhibit that misalignment of weft yarns of the membrane partly contributes the loss of the strength in weft direction. The results of observations by microscope and tensile tests of single yarns reveal that the difference of the strength in warp and weft directions is caused by the degradation of weft yarns by heating process of polymer film coating on the fabrics in addition to the misalignment of yarns.
Low-power Hall thruster flowfields were calculated using a simple one-dimensional model to understand plasma characteristics and ion acceleration processes and to predict thruster performance. The influences of magnetic field strength and acceleration channel length were mainly examined. The thruster model for calculation is the THT-IV low power thruster developed in Osaka University. Generally, ions were produced in an upstream region from the anode to some axial location of the acceleration channel, and then they were intensively accelerated in a region downstream just from the ionization region. With too short channel, ionization began downstream just from the anode, and then ion acceleration also occurred in the same region, resulting in poor ion flux and low thrust performance. In large channel length, the channel was long enough to produce a fully-ionized plasma, and efficient ion production and acceleration occurred. When the magnetic field strength increased in the channel, ionization occurred in a more upstream region, and ion acceleration began in the same region; that is, ionization and acceleration overlapped in the relatively long region. On the other hand, with a weak magnetic field ion production and acceleration, intensively and efficiently, occurred in their thin regions. Furthermore, we tried to include unclear anomalous electron diffusions by changing a Bohm diffusion coefficient at each high magnetic field strength in order to fit a calculated performance to the measured one. The calculated discharge current almost equaled the measured one, and the thrust characteristic also agreed well with the measured one.
The effect of heat loss on the instability of premixed flames is studied by two-dimensional unsteady calculations of reactive flows, based on the compressible Navier-Stokes equation. We take account of hydrodynamic and diffusive-thermal effects as to the intrinsic instability of premixed flames. A sufficiently small disturbance is superimposed on a planar flame to obtain the relation between the growth rate and the wave number. As the heat loss becomes larger, the growth rate decreases and the unstable range narrows. This is because that the hydrodynamic instability generated by thermal expansion becomes weaker. To study the unstable behavior of cellular flames, the disturbance with the linearly most unstable wave number, i.e., the critical wave number, is superimposed. The superimposed disturbance evolves, and the cellular-flame front is formed, owing to intrinsic instability. The lateral movement of cellular flames is observed at low Lewis numbers, and the behavior of cellular-flame fronts becomes more unstable for non-adiabatic flames. With an increase in the heat loss, the burning velocity of a cellular flame normalized by that of a planar flame increases at Lewis numbers lower than unity. When the Lewis number is not less than unity, on the other hand, the flame-velocity increment decreases by increasing the heat loss.
Flow visualization and surface pressure measurements have been conducted on a 45º delta wing in roll to examine their nonlinear characteristics of rolling moment that cause self-induced oscillations in a post-stall state. These flow patterns were analyzed by comparing with the results of static aerodynamic force measurements. At a roll angle of around 75deg, the flow pattern changes from separated to attached flow with a separation bubble, which is considered to make a critical state in the characteristics of rolling moment, where energy is supplied to the self-induced oscillation process.
The characteristics of rolling moment in a 45-deg delta wing with a leading-edge flap were studied to examine its effects in pre- and post-stall regimes, where conventional control surfaces are ineffective. A small flap with a height of 2mm was employed to control the flow, which was placed on the round leading-edge of the delta wing from 10 to 75% chord. Wind-tunnel experiments were carried out for static aerodynamic force measurements and flow visualization. In the pre-stall regime, it is observed that the single flap can produce about ±0.01 of rolling moment coefficient, which is sufficient for flight control. On the other hand, in the post-stall regime, its rolling moment characteristics are quite nonlinear and complex. The flap can basically reduce the unsteady moment by interfering with the development of a leading-edge vortex, or promoting the flow attachment to the wing surface.