The boundary layer transition caused by the cross flow instability over a highly swept wing was controlled by using a DBD plasma actuator. The plasma actuator installed near the leading edge, and induced the flow to suppress the cross flow velocity that causes the transition on the highly swept wing. A low-speed wind tunnel tests were performed to understand the effects of the plasma actuator for a 60 degrees swept wing on Re=487000. The results were shown that when plasma actuator is activated the transition location delayed to downstream than no actuation of the plasma actuator. It means that the plasma actuator contributes to reduce the cross flow velocity component hence the boundary layer transition can be delayed to downstream. With increasing the voltage of the plasma actuator, the displacements of the transition locations are also increased. This trend was also observed at different free-stream velocities.
Supersonic wind tunnel tests of flexible parachutes whose canopies had a hemispherical shell configuration were conducted. This study was performed to explore the mechanism of flow field oscillation and vibration of canopy movement that were caused by the interaction between the supersonic flow and flexible fabric of the canopies. Effects of the flexibility and gas permeability of fabrics to the drag characteristics of the parachutes were investigated. Three kinds of fabrics (i.e. thin nylon, thick nylon and polyester) were used to produce the canopies. Sizes of canopies were also changed in three steps (nominal diameter D0 = 30, 40, 50[mm]) to investigate the variation of the drag. A load cell was installed in the capsule to measure unsteady and time-averaged drag values of the parachute. Schlieren images by a high speed camera provided us with visualized flow fields showing shock deformations. Moreover, a three-dimensional motion capturing system was used to evaluate the movement of the canopy. The process of parachute ejection from the capsule was also examined. As a result, it was indicated that canopy fabrics with higher gas permeability induce lower mean drag values. On the other hand, the lower flexibility, the larger drag fluctuation is. Furthermore, the spectrum of the canopy movement showed the similar profiles to the spectrum that of the drag fluctuation indicating the direct link between the canopy movement and its drag fluctuation.
The feasibility of smooth merging of descent air traffic stream by air traffic controllers' instructions is investigated through numerical simulations. A flight route segment for precise aircraft interval control is especially focused in this paper. A fixed flight route is applied to improve the time interval estimation accuracy, and only the flight speed instruction is given to the aircraft. Even through a simplified traffic control algorithm, the feasibility of a precise interval control is demonstrated by numerical simulations. In addition, to assure the safety, a route structure is newly proposed to enable aircraft to maintain the safe distance even when the time interval becomes insufficient. Finally, the metering position is optimized so as to enable the air traffic controller to avoid the workload overconcentration.
In this paper is presented a microgravity experiment system utilizing a high altitude balloon. The feature is a double shell structure of a vehicle that is dropped off from the balloon and a microgravity experiment section that is attached to the inside of the vehicle with a liner slider. Control with cold gas jet thrusters of relative position of the experiment section to the vehicle and attitude of the vehicle maintains fine microgravity environment. The design strategy of the vehicle is explained, mainly referring to differences from the authors' previous design. The result of the flight experiment is also shown to evaluate the characteristics of the presented system.
Diverter-less intake for supersonic aircraft is examined as a modern design technique of propulsion/airframe integration. In this study, a design guideline for the compression ramp in an external compression supersonic intake mounted on a low diverter or without diverter is examined by CFD analysis. We pursue the optimum configuration of the ramp which minimizes the boundary-layer flowing into intake without failing to decelerate the supersonic flow captured by an intake. The flow field over a single-stage rectangular wedge mounted on a flat surface was investigated under the free stream Mach number of 1.6. The results show that, under a given cross-sectional area of the intake throat, the width and angle of the ramp are important parameters to determine the optimum configuration. In order to decrease the mass flow rate of boundary-layer which flows into an intake, the ramp width should be small as long as the minimum decelerating demand is satisfied. The excessive large angle is not allowed because it induces substantial pressure loss of the main flow. In case of diverter-less configuration, the ramp width should be designed smaller than that in case of configuration with diverter to minimize the incoming boundary-layer.
The pintle injector is one of the most promising candidate for propellant injection systems of liquid rocket engine combustors due to the throttling capability and simple structure. However, combustion characteristics of pintle injectors are still unclear. Therefore, combustion experiments are conducted for an ethanol/liquid oxygen rocket engine combustor with a planar pintle injector which simulates the injection configuration of a pintle injector and enables optical measurements at Pc=0.40MPa and O/F=1.08-1.56. Direct images of the flame structure and CH chemiluminesence are observed through an optical window using high speed imaging techniques. Backlit images of the spray structure are observed. Strong CH chemiluminescence is observed in the vicinity of the impinging point of the two propellants. Luminous flames are observed in the vicinity of the faceplate and the upper wall of the combustor. It is observed that atomization process of the planar pintle injector proceeds two-dimensionally unlike conventional impinging injectors. A periodic atomization behavior is observed with the frequency of approximately 700Hz, being equal to the frequency of the Kelvin-Helmholtz instability.
Recently, shock-tunnel experiments have been conducted at high-pressure and high-enthalpy conditions such as a reservoir pressure of 50MPa and a reservoir enthalpy of 20MJ/kg in order to study laminar-to-turbulence transition on hypersonic vehicles. In those experiments, unexpected large wall heat flux to test models was measured, which was not observed at conventional pressure conditions. The cause of the heating augmentation remains an open issue. In this study, the influence of chemical nonequilibrium in the flowfield around test models on the heating augmentation was investigated by computational fluid dynamics (CFD) simulation, and it was found that the influence is small.