This paper describes the effectiveness of the direct simulation for the sonic boom prediction over the whole computational domain from the body to the ground and the nature of the sonic boom propagation for the hypersonic vehicle. Both the near and far fields around an axi-symmetric paraboloid are numerically obtained by the axi-symmetric Euler analyses assuming the uniform atmosphere. Moreover, the three dimensional Euler analyses with the gravity term have been conducted to consider the variation of the atmospheric properties with the altitude. Consequently, it is confirmed that the direct simulations are the same level of accuracies of waveform parameter method. Furthermore, the nature of the sonic boom propagation does not change up to Mach 7 in the uniform atmosphere and Mach 5 in the real atmosphere, when the small disturbance is assumed. Therefore, the evaluation method for the sonic boom propagation at the supersonic speed is applicable to predict the sonic boom strength at the hypersonic speed. At the ground level, the sonic boom intensity generated by the Mach 5 flight at 25km altitude is less than the intensity by the Mach 2 flight at 15km altitude.
The principal function of a control system for a small vehicle is to generate or counteract its angular momentum. A straightforward approach to exerting control torque is to use three separate flywheels with motors in a mutually orthogonal arrangement. This paper describes the development of a three-dimensional reaction wheel using a spherical rotor that can reduce the number of flywheels from three to one. Therefore, the proposed system can be applied to a small satellite with space and weight limitations. The system consists of the spherical rotor, three piezoelectric actuators as the stator, and optical sensors. The spherical rotor can rotate around arbitrary axes without a very complex mechanism using gears, links, and special mechanism. A feedback control system is designed to control the angular velocity vector of the spherical rotor. The performance of the proposed system is verified through preliminary experiments.
The traffic control performance of an air traffic flow on a continuous descent operation (CDO) is discussed. On a CDO, aircraft are able to control the time to arrival the airport by changing its descent rate with maintaining the idle thrust. It is possible to optimize the punctuality by leading aircraft to fly on their scheduled time. In such traffic control strategy, the traffic control performance, such as separation control accuracy and total traffic flight time, are determined by the scheduled time. Through numerical traffic control simulations on the traffic control performance, it is clarified possible to minimize the total traffic flight time by selecting an appropriate scheduled time without losing the separation control accuracy. It is also clarified possible to estimate the total traffic flight time, and a practical approach to determine the scheduled flight time also presented.
Drag reduction performance over a blunt-body by a combination of a conical spike and repetitive energy depositions is investigated. Experiments are conducted in a Mach 2 supersonic flow in an in-draft wind tunnel, varying the length and the apex angle of the spike on a flat head body and the repetitive frequency of laser pulse energy depositions from 0 to 60kHz. Computational fluid dynamics calculations are done to diagnose the flow fields. Comparison is made between the experiment and calculation with respect to visualized flow fields and to the drag. When the length of the spike is shorter than the shock stand-off distance over the body without the spike, the effect of the spike is significant in low repetitive frequencies of up to 40kHz. In even higher repetitive frequencies, the impact of the spike becomes weak; the drag reduction is primarily attributed to energy deposition.
A high density air corridor is expected to be an air space where aircraft capable of airborne self-separation are allowed to fly into the same direction. A self-separation algorithm in a high density air corridor that is feasible for the human pilot manual control is discussed in this study. In addition, the corridor width limitation is also considered to definitely prevent any conflict against the aircraft outside the corridor. Through a series of the traffic simulation, it has been clarified that an algorithm that indicates the fixed heading change to the pilot is able to achieve a safe corridor operation in combination with flight speed control. It is also clarified that the information of the intended flight speed and the collaborative separation control are indispensable for the air corridor efficient operation.