This study aims to investigate the incremental thrust in a diagonal magnetohydrodynamic (MHD) accelerator as a function of the number of segmented electrodes, the applied magnetic-flux density, and the different setting of diagonal angle. The peak incremental thrust obtained from the numerical result was agreement with that of the experimental result. For understanding the characteristics of current vector distribution in a diagonal MHD accelerator, we calculated the current vector as the function of a number of segmented electrodes, the applied magnetic-flux density and the different setting of diagonal angle. The simulations showed the current vector distribution inside the MHD channel as well as the current flow crossed into tungsten wires as a diagonal connection of the MHD channel. From these numerical simulations, the tilt angle of current vector distribution was changed by Faraday current in the MHD channel, which was controlled by the magnetic field.
The centrifugal compressor is an essential part of the auxiliary power unit (APU) for airplanes and helicopters. As aircrafts are sometimes required to operate at high altitudes, the aerodynamic condition of the gas turbine and APU lies at low Reynolds numbers. This study presents numerical simulations to investigate the effects of low Reynolds numbers on the flow and performance of a centrifugal compressor, including the impeller, diffuser and volute. For the reference Reynolds number (8.4×105), the numerical results agreed well with the experimental measurement in total pressure ratio. It was found that the performance of the overall compressor decreases slowly as the Reynolds number decreases, but drops significantly below the threshold of 200,000. The flow inside the impeller didn't separate in spite of thick boundary layers, even at the lowest Reynolds number (8.4×104). In this study, it was found that the diffuser is the most susceptible part for separation caused by low Reynolds numbers. The large separation in the diffuser vanes degrades the flow, and decreases the efficiency of the diffuser and volute successively.
While balloon launch is one of the most cost-efficient ways to realize a supersonic flight experiment, it presents some issues for the controller. D-SEND#2 is one flight experiment of this kind which was carried out in 2015. An unpowered test vehicle was lifted to an altitude of 30 km by a balloon and then released. After separation, the vehicle's onboard flight control computer selected a target Boom Measurement System (BMS) according to the separation point. The vehicle then autonomously flew to the BMS selected and established the prescribed sonic boom measurement flight conditions. The design of the guidance, navigation, and control system for the D-SEND#2 flight test was exceptionally challenging, and it was solved by a combination of a sophisticated guidance law and a control law based on dynamic inversion and time scale separation. This paper describes a controller design method for a balloon-launch flight experiment and applied it to a D-SEND#2 control system design. Flight results are presented to show the effectiveness of the controller design method.
The effects of Mach number at Re = 3,000 for different airfoils (NACA0012, NACA0002, NACA4412, NACA4402) with thickness and camber geometries are investigated for the propeller blade design of a Mars airplane. The present study shows that thin and cambered airfoils have larger variations in Cl than symmetric airfoils. As for thin airfoils, Cl at higher α has rapid increases when the M∞ is low. This is because the flow separation occurs at the leading edge, and the flow is reattached on the airfoil surface. However, the rapid increase in Cl disappear as M∞ increases because the flow reattachment does not occurs. As for cambered airfoils, the decrease in Cl becomes larger than that on the symmetric airfoils when M∞ is higher. This is because Cp near the leading edge on the lower surface is smaller than that on the upper surface and the high-speed region on the lower side of the leading edge is enlarged as M∞ increases. Then, the Mcr at Re = 3,000 tends to be larger than that predicted by linear theory.
In this study, tests were performed using a newly developed combustion chamber for a rotating detonation engine to study the effects of reactivity of the mixture as related to the cell width and CJ velocity, and the total mass flow on the stability of rotating detonation wave (RDW) propagation. For the reactant mixtures, 2H2 + O2 + βN2 was used, where the dilution ratio β was varied from 0 to 3.76 to change the cell width and CJ velocity. The experimental results showed that stable operation was achieved when the average total mass flow rates were larger than 170, 200, and 350 g/s for β = 1.36, 2.65, and 3.73, respectively, and that the velocity of the RDWs decreased as decreased. Regardless of the mixture composition, a stable mode was obtained when the height of the reactant mixture normalized by the cell width, h/λ, was larger than 3. There was a minimum value of that adjusted h/λ to enable the stable propagation of RDWs.
In this study, the effect of creases on the out-of-plane stiffness of a spinning circular membrane was investigated. A circular polyimide membrane, 600 mm in diameter and 25 µm in thickness, was used. Fanfold and flat-creased circular membranes with 12 fanfold creases in the radial direction, as well as a flat circular membrane without creases, were considered. First, forced vibration experiments on the spinning membranes were conducted in a vacuum chamber and the relationships between the rotation speed and first resonant frequencies were measured to examine the variations in stiffness due to creases. Subsequently, large deformation analyses of the membranes under gravity and eigenvalue analyses of the equilibrium states were conducted using a commercial nonlinear finite element software (i.e., Abaqus), and the fundamental modal frequencies were obtained and compared with the experimental results. The fundamental frequencies without gravity were also numerically analyzed. The author found that the fundamental frequency of the fanfold membrane was almost independent of gravity. Finally, the cause of variation in the fundamental frequencies of the membranes is discussed by estimating the stiffness due to the three-dimensional equilibrium shapes.