This paper analyzes the feasibility of time-based metering operations for domestic flights in Japan, which have shorter flight times than international flights. For metering air traffic, aircraft are required to adjust their fly-over times at specified fixes. Speed control is typically used to adjust the fly-over time without stretching the lateral path. This study applies flight-level change in addition to speed control to increase the achievable airborne delay. The achievable airborne delay using speed control and flight-level change is evaluated statistically based on past actual radar tracking data. Through illustrative numerical simulations for the domestic flights to Tokyo International Airport, the achievable delays can be more than doubled and higher compliance rates are expected when changing the flight level in addition to speed control. Moreover, the potential benefit of saving fuel using speed control is evaluated, and a fuel savings of 2–4% is expected on average. Based on the analysis in this study, the maximum potential achievable delays and feasibility of time-based metering for domestic flights in Japan can be evaluated.

A sabot is used in a supersonic accelerator to reduce the in-bore balloting in the tube. Sabot petals are separated from the projectile after muzzle discharges; however, this sabot separation induces flight deviation caused by the shock wave interaction with the projectile. In this study, we investigate the three-dimensional (3D) shock wave interaction between the projectile and the sabot based on a previous experimental configuration by using 3D computational fluid dynamics coupled with rigid-body dynamics. We observed three types of shock wave interaction on the projectile: namely, shock wave oscillation, recompression shock wave attenuation, and shock wave sweep. The shock waves from the projectile and the sabot oscillate around the projectile tip because the gap between the projectile and the sabot is too small for the ambient air to pass through. This oscillation induces a significant aerodynamic perturbation on the projectile and the sabot. Multiple shock wave reflections appear between the projectile and the sabot petals after the oscillation ends. These multiple shock wave reflections generate a complex flow field between the projectile and the sabot, and an unsteady aerodynamic perturbation on the sabot.

Neutral particles that flow back into a Hall thruster during ground tests are designated as ingestion particles. The source of the ingestion particles is apparently the chamber wall on which the ion beam is incident. As described herein, we propose a method of suppressing the ingestion particles using a beam target, designed to dump the beam, acting as a mirror to guide the reflected particles to the cryopump. Based on our earlier study involving the dependence of the pump capture coefficient of the cryopump on the angle of particle inflow and the surface reflection characteristics of metal targets for Xe ions, we present design guidelines for the distance between the Hall thruster and the beam target, the cone angle of the beam target, and the cryopump position. The ingestion particle suppression effect obtained by installing a conical beam target in an actual chamber was evaluated by applying 2D3V-DSMC calculations. For the 2-m-diameter, 3-m-long space chamber with 30-in-wide cryopumps set all around the chamber, the calculated ingestion mass flow rate to the thruster with a conical beam target is reduced to one-third of that with a flat target.

Implicit large-eddy simulation/Reynolds-averaged Navier-Stokes hybrid simulation of sheet-like hydrogen jets in a supersonic crossflow are performed to investigate jet mixing, focusing on the difference in flow structures between sheet-like jets and round jets. The simulation is validated with a helium jet experiment in terms of the mean concentration. The numerical results showed good agreement with the experimental results. A characteristic of injection from the sheet-like jet exit is the spread of the windward jet toward the spanwise direction owing to the strong interaction with the freestream, while the leeward jet highly penetrated the freestream. In the investigation on jet mixing using different jet exit geometries, it was found that the sheet-like jet has a lower mixing efficiency compared with the round jet. The two mixing characteristics of the sheet-like jet are (i) a large jet cross-sectional area, and (ii) a weak turbulent mixing in the windward shear layer. As the effect of the momentum flux ratio on the jet mixing with sheet-like jet port, the mixing is enhanced with increasing the momentum flux ratio.

In the present study, the visualization of compressible flow around a particle/particles including wake vortices and drag estimation were conducted through shock-particle interaction experiments. An experimental method that can investigate flow over isolated and clustered particle(s) (with a minimum diameter of 0.3 mm) interacting with a planar shock was established. For flow visualization, the Mach number (M) and Reynolds number (Re) based on the relative velocity between the particle and the quantities behind the planar shock wave were 0.46 ≤ M ≤ 1.24 and 3500 ≤ Re ≤ 9800, respectively. The present measurement system succeeded in visualizing flow structures not only for shock waves, but also wake structures formed behind the particle(s) under subsonic and transonic conditions, and the Mach number effect was provided. The mean drag coefficient was estimated from the time-position data of the particle at 3100 ≤ Re ≤ 9800 and M = 0.46. The estimated drag coefficient was close to that of the value estimated by the drag model and previous experiments. The flowfield around clustered particles was visualized and its breakdown process was observed. The particle cluster dispersed due to aerodynamic interference. Particularly, the particles located on the upper side of the particle cluster moved upward against the gravitational force.

Proper flap usage is proposed to improve the hovering performance of a winged helicopter. The download on a winged helicopter was experimentally investigated using a simplified model consisting of a rotor and a wing without a fuselage. It is shown that the flap angle minimizing the download, when left and right sides of flaps are deflected to the same angle, is less than the angle, which minimizes the projected area on the horizontal plane. This result is consistent with the conclusions of existing studies under similar conditions. When a difference in each flap angle was allowed, the flap angles, which minimize the download, are different between left and right. The swirl velocity in the rotor wake can be regarded as a factor in determining the optimal flap angles for reducing download. Taking the swirl into account, we propose a simple method to estimate the wing download when the flaps are used. Although the method based on the model of two-dimensional jet and wall is too simple to represent the complex aerodynamic interaction, results calculated using the proposed equation are in good agreement with the experimental results.