The aerodynamic characteristics and the effects of winglets of a tapered supersonic biplane during the starting process have been investigated through Experimental and Computational Fluid Dynamics (EFD/CFD). Three types of the tapered biplane model were used: without winglet (type-N); with the winglet which covers only the aft-half of the wing tip (type-A); with the winglet which covers the entire wing tip (type-B). Experiment was conducted in the supersonic blow-down wind tunnel with 600mm × 600mm cross section located at the High-speed Wind Tunnel Facility of Institute of Space and Astronautical Science, JAXA. The flow conditions covered from M∞ = 1.5 to 1.9 with increments of 0.1. Pressure-Sensitive Paint was applied to measure pressure distributions on the surface of supersonic biplane models. CFD simulations were conducted to compare with experiment and to investigate effects of the Mach numbers in detail. The tapered biplane without the winglet was found to start between M∞ = 1.8 and 1.9. The difference of the starting Mach numbers between type-N and type-A was small. On the other hand, the starting Mach number of type-B was about 0.05 higher than that of type-N.
Plasma flowfields and performances of an MPD thruster (MY-II thruster), which uses hydrogen as a propellant, are studied by solving axi-symmetrical two-dimensional magnetoplasmadynamic equations. The three-temperature model including the translation Ttr, vibration Tvib, and electron Te temperatures is incorporated into the flow solver. When the mass flow rate (m) is 1.37g/s, there is reasonable agreement on the thrust with measured data, especially at a discharge current (Jdis) of 7, 8kA. Under the conditions of m = 0.4g/s and Jdis = 5kA, the calculated thrust, specific impulse and thrust efficiency are 7.50N, 1,911s and 21.3% (without considering sheath voltage drop), respectively. The calculated flow shows a temperature nonequilibrium state (Te = 2.53eV, Tvib = 1.32eV, Ttr = 0.60eV) at the edge of the straight part, and it is found that the relaxation time between the vibration and the electron energy is equal to the characteristic time of the flow at (z, r) = (30mm, 20mm). Along the symmetrical axis, the dissociation and ionization fractions reach 1.0 (fully dissociation) and 0.2, respectively. Because the discharge current path by the three-temperature model can explain the important feature of hydrogen MPD (current expansion to the downstream), it is concluded that the three-temperature model can reproduce the experimental results.
A decentralized control of an air traffic flow is discussed. This study aims to clarify a fundamental strategy for an unidirectional air traffic flow control considering the flight speed distribution. It is assumed that the decentralized control is made based on airborne surveillance systems. The separation control between aircraft is made by turning, and 4 types of route composition are compared; the optimum route only, the optimum route with permissible range, the optimum route with subroutes determined by relative speed of each aircraft, and the optimum route with subroutes defined according to the optimum speed of each aircraft. Through numerical simulations, it is clarified that the route composition with a permissible range makes the air traffic flow safer and more efficient. It is also shown that the route design with multiple subroutes corresponding to speed ranges and the aircraft control using route intent information can considerably improve the safety and workload of the air traffic flow.
Unsteady flow characteristics in a dual-bell altitude compensation nozzle at low altitude operation modes are examined. At the low altitude operation mode, a jet separation point is fixed at the nozzle wall inflection. However, experimental and numerical results show that three modes of periodic jet fluctuations take place at certain range of nozzle pressure ratios. The lowest frequency mode is a symmetric modes and is considered to be caused by the acoustic resonance in longitudinal direction in the extension part of the nozzle. Two kinds of asymmetric modes have higher frequency than the symmetric mode. According to the numerical results, one of them is a jet screech tone caused by the convection of large scale vortices beside the separated jet. The other mode has the same frequency with a resonance mode in the diametrical direction of the cross section of the extension part.
Solar wind plasma behavior and thrust of a magnetic sail under the condition with interplanetary magnetic field (IMF) are examined by time-dependent, two-dimensional, X–Y Cartesian, hybrid particle-in-cell (PIC) simulations. Magnetic sail is a propellant less propulsion system proposed for an interplanetary space flight. The thrust force is produced by the interaction between magnetic dipole field artificially generated by superconducting coils in a spacecraft and a solar wind. In the present simulations, the ratio of ion Larmor radius at the magnetopause to characteristic length of the magnetosphere is set to 0.1, and IMF strength is set to 0 and 10nT. As simulation results, magnetic reconnection occurs due to superposition of IMF and dipole field in the solar wind flow field. The reconnection points depend on the direction of IMF and those have an important role in the formation of shock wave. When IMF is perpendicular to the solar wind flow direction, the thrust acting on the spacecraft increases compared to the case without IMF. When IMF is parallel to the solar wind flow direction, lift force is generated on the spacecraft. These phenomena are attributed to the difference in location of magnetic reconnection point depending on the direction of IMF.
It is expected that the use of GNSS technology in urban areas will be increased. Since there are many buildings in urban areas, the direct signal from satellite occasionally can be reflected or diffracted. As a result, we are faced with big errors due to multipath. It is strongly required to improve reliability considering the use of GNSS for future ITS. In order to do that, the ability to detect the inferior observations of GNSS is required. The objective of this paper is to improve reliability and availability in RTK-GPS. Firstly, this study reveals the relationships between reliability and availability according to the quality check of GPS observation data. For example, reliability decreases when the measurement calculation is done with four numbers of satellites compared with five numbers or more of satellites. Then the detection algorithm to remove the inferior observations of GPS is proposed. The performance was checked by using raw GPS data obtained in major cities and it is confirmed that the performance was improved by using our proposed method.
This paper proposes a method for identifying the location and force history of an impact force acting on plate structures. The identification method is an experimental one so it does not require any analytical model of the structure. The impact location is identified using arrival times of the flexural wave to the PZT sensors. In order to determine the arrival times accurately and rapidly, an analog band-pass filter is used to obtain the wave with a specified frequency. Experimental transfer matrices, which relate the impact force and the sensor responses, are used to identify the force history. Here, the transfer matrices are preconstructed from the measured data obtained by impact tests conducted with an impulse hammer. The force history is identified by minimizing the deviation between the measured sensor responses and the responses estimated from the experimental transfer matrices. In order to verify the validity of the proposed method, impact force identification of aluminum plates and CFRP laminated plates are performed experimentally. The results reveal that the location and force history of the impact force can be identified accurately in real time using the proposed method.
Recently, acoustic analysis using the Linearized Euler Equation (LEE) on multi-block structured or unstructured mesh is focused. However, mesh generation around complicated geometries takes time on structured mesh and cost of high order calculation gets larger on unstructured mesh. In this research, a LEE code for aeroacoustic analysis is developed on block structured Cartesian mesh of Building-Cube Method. To make an accurate calculation, the Immersed Boundary Method is implemented for wall boundary treatment and high order Lagrange interpolation is implemented at the Cube boundary for data exchange. This code is validated through acoustics scattering problems around cylinders and the calculational errors are compared. The results show good agreement with analytical solutions and the usability of these methods.