Authors have proposed a flutter prediction method based on a new criterion for the stability margin of aeroelastic systems. The analysis using a two-dimensional wing model showed that the new parameter had a superior property as a flutter predictor to the modal damping used conventionally in most flutter predictions. The purpose of this work is to apply the new method to flutter testing data and to examine the applicability of the method in the actual situations. The data used here are of a supersonic wind tunnel flutter testing. The results showed that the new parameter gave a good prediction of flutter boundary by linear fitting. In addition, the estimate of the new parameter was not affected so much with the tunning of data processing conditions such as the bandwidth of a filter or the structure of an identification model.
A method of carrying out arc-discharges inside a combustor, Direct Arc Injection Method, has been developed to ignite a methane fuel in supersonic airflows. Some air carrier-gas injected from between the cathode and the anode was used to push off the arc to the main airflow in the method. In this study, air-methane mixtures are applied to the carrier gas to promote the combustion and the fundamental aspects of the combustion promotion mechanisms are investigated by experiments and calculations. The results indicate that in addition to arc-discharge, the air-methane carrier gas generates more heats and radicals, mainly H, O, N and OH, from the combustion reaction of itself and the H radical is, especially, the most effective of those radicals on shortening the ignition delay time of air-methane reaction.
The effects of fracture modes on the kinetic energy absorption were studied experimentally on thin-walled circular tubes under dynamic axial compression. Emphasis was put on stable progressive fracture of these shock-isolating structural elements, in order to obtain moderate load histories toward protection of the objects from serious impact damage. Some of the results of impact tests on tubes with surface grooves or with other edge configurations are summarized in this report.
The influence of intrinsic instability on the flame velocity is studied by two-and three-dimensional, unsteady calculations of reactive flows, which are based on the compressible Navier-Stokes equation. We consider three basic types of phenomena which are responsible for the intrinsic instability of premixed flames, i. e., the hydrodynamic, diffusive-thermal, and body-force effects. As intrinsic instability becomes stronger, the flame velocity of cellular flames is increased. The increment in flame velocity of three-dimensional flames is about twice that of two-dimensional flames. When the Lewis number is unity, the flame velocity is almost proportional to the flame-surface area. When the Lewis number is lower than unity, on the other hand, the increment in flame velocity is larger than that in flame-surface area. The reason is that the increase in local consumption rate of the unburned gas at a convex flame front with respect to the unburned gas exceeds the decrease at a concave flame front.
Acoustically excited jet diffusion flame and unburnt jet in quiescent air are investigated experimentally to provide detailed information about combustion characteristics and the jet structure. The hydrogen jet diffusion flame and unburnt jet are acoustically excited by monotone sound wave generated by a loud speaker. For the unexcited jet diffusion flame, the hysteresis behavior in the flame lift-off and reattachment, and the sudden increase in lift-off height are observed. Applied the acoustic excitation using a specific range of frequency, the jet velocity at which the transition from laminar to turbulent flame occurs is lowered significantly. Also, the flame shortens its original length and is widened in the incident direction of the sound wave. Furthermore, the flame with branched tip is observed in narrower region of the Strouhal number and the Reynolds number. It is also found out that branching of the unburnt jet is created in a region of lower Strouhal number and lower Reynolds number than the branched tip flame.
We discuss the influence of the gravity gradient on satellite orbits. Regarding a satellite as an inertial ellipsoid, not point mass, the gravitational force acting on it includes the force due to the gravity gradient, which we call “gravity gradient force.” The gravity gradient force depends on the inertial matrix of the system and changes according to the attitude and the configuration. In this paper, we analyze planar motion of a satellite under the influence of the gravity gradient and apply the effect to controlling the semi-latus rectum or the eccentricity vector of the satellite orbit. By substituting the formula of the gravity gradient force into the equation of orbital perturbation, we obtain the time differentials of the orbital elements and the efficient attitude motion of the satellite for the orbit control. Finally, we numerically examine the motion and control of the satellite under the gravity gradient force.