The flow fields of the jets opposed into uniform streams include very large diffusion. Investigation of those flow fields is important to estimate the characteristic of a high performance combustor and diffusion of the jets etc. Many researchers have reported the fact that those flow fields were characterized by the re-circulation zones shown by turning back streamlines and the stagnation points. In those flow fields, however, we cannot find increasing of static pressure due to change the direction of streamlines. On the contrary, the decreasing of static pressure is seen in the flow field. Now we attempt to explain these experimental results by characteristic of the structure of turbulence in the mixing layer of the jets. In this article, the diffusion of the jets is investigated by introducing relative diffusion and interaction between the turbulence in the mixing layer of the jets and that in the outer flows in view of chaotic feature.
This paper concerns motion control of redundant manipulators on spacecraft at the acceleration level. Acceleration-level control of redundant manipulators often causes the peculiar problems such as the instability of local torque optimization and the end-motion joint velocities. One of the solutions to the problems is the acceleration-level control based on a velocity-level control method, which is derived from time differential of a velocity-level solution guaranteed not to cause the problems. In this paper, a new acceleration-level control method is proposed, which accomplishes the end-effector operation as a primary task and minimizes the disturbance on the satellite attitude as a secondary task. Numerical examples verify its superiority over other acceleration-level control methods and apply it to control for capturing a drifting target.
The spinning experiments of a flat plate wing were conducted at the low speed wind tunnel of Nagoya University with a vertical exit test section. The spin rate of the flat plate wing in the free rotation mode was measured as well as surface pressure distributions on the spinning flat plate wing. Spin rate increases with sideslip angle. In addition, when the wing has a sideslip angle, the upper surface pressure of the windward wing-half decreases compared with that of the leeward wing-half. This asymmetric pressure distribution causes the spinning motion of the flat plate wing. From the pressure distributions and flow visualizations, it is evident that a leading edge vortex is generated near the tip of windward wing-half and reduces the pressure on the wing-half. It is also found that at the equilibrium spin rate, the pressure difference between upper and lower surfaces, ΔCp, shows a nearly symmetric distribution with respect to a centerline in the spanwise direction. At a lower spin rate than the equilibrium one, the value of ΔCp on the windward wing is larger than that on the leeward wing, whereas at a higher spin rate, the reversal of its distribution occurs.
The main purpose of this study is to reveal a transition mechanism between two typical combustion modes called ‘weak-combustion’ and ‘intensive-combustion’ observed in the firing tests of scramjet engines at Mach 4, 6 and 8 conditions of Ramjet Engine Test Facility (RJTF). For this purpose, flow structures in the combustor and their changes during the transition of the combustion mode are investigated by cold flow tests as well as numerical simulations. These results and the firing test results led us to conclude 1) that transition from ‘weak mode’ to ‘intensive mode’ is the consequence of the mutual interaction between enhancement of fuel/air mixing as well as combustion within the boundary layer and the growth of the boundary layer separation area and 2) that in the present engine principal fuel/air mixing and combustion strongly depend on the occurrence of large-scale boundary layer separation, thus the resulting principal combustion is characterized to be subsonic combustion within the separated boundary layer.
A real-time flutter prediction method based on nonstationary random response is proposed. Instead of the modal damping, which is commonly used as the stability criterion in most flutter tests, the new parameter proposed by authors is used to evaluate the stability margin of aeroelastic systems. Firstly, the property of the parameter estimated recursively is investigated by simulation using a bending-torsion wing model. Then the method is applied to nonstationary supersonic wind tunnel flutter test data, in which the dynamic pressure is increased at a constant rate. The result is compared with those of the existing flutter prediction methods.
Japan has been investigating the use of an airship system that will function as a stratospheric platform (SPF) for applications such as environmental monitoring, communications and broadcasting. If pseudolites were mounted on the platforms, their GPS-like signals would be stable augmentations that would improve the accuracy, availability, and integrity of GPS-based positioning systems because the airship network would cover all of Japan. The accuracy of the pseudolite positions would be a limiting factor for such a service since the pseudolite ‘ephemeris error’ is more serious than GPS due to the lower height of the platform. In this paper, a conceptual design of the SPF-based augmentation system is first introduced. Then some schemes for estimating the pseudolite position are described.