Flame-holding experiments of newly devised struts for the scramjet engine were carried out in supersonic airflow of Mach number 1.5. The basic configuration of struts consists of two parts into which a general strut with steps was divided at steps. The intervening space between those two parts can be changed and hydrogen gas is issued from the rear end of the front strut to the intervening space. Based on the flame-holding mechanism explained in authors' preceding reports, three improvements were made in order to widen the flame-holding region: (1) To introduce much air into the intervening space, fuel hydrogen was partially premixed by air. (2) Also, air was taken in from intake slits provided on the front strut against supersonic airflow. (3) On the contrary, in the case of the large intervening space, to prevent excess air to entering into the intervening space, recess was equipped around the fuel port. It was found that, according to the overall equivalence ratio in the intervening space, three techniques were quite reasonably worked and the flame-holding regions were widened.
Aerodynamic configuration of a cone-derived waverider is designed according to the Taylor-Maccoll equation. Flow fields are numerically calculated at an on-design flow condition of the Mach number of 5.5, and the aerodynamic characteristics are estimated. The on-design model is manufactured using a numerical controled machine. In a hypersonic wind tunnel testing at the free stream Mach number 5.5 and the unit Reynolds number of 4.34×106(/m), flow fields are observed with Schlieren photographs and oil flow pattern; also aerodynamic characteristics are measured by a three-component balance. As a comparison, a off-design model with a flat lower surface is made and used for tests at the same flow conditions. The results show that shock wave is well attach to the leading edge of the on-design model at zero angle of attack; streamline on the lower surface is conical and cross flow is not observed. The maximum L/D ratio is found to be about 4.0 at the angle of attack of around -1°, which is higher than that of the off-design model.
The objective of this study is to analyze the flame propagation under the interaction between fluid mechanics and chemical kinetics in a counter shear layer. First, a large-scale Kelvin-Helmholtz instability is triggered by initially-imposed linear perturbations to form a multi-stratified vortical layer. Second, mixed reactants due to such a stratified vortex are ignited where flame propagation under the effect of instability growth is observed. Three different ignition points are selected to examine combustion efficiency. The ignition point selected in a vortex core shows 1.7 times CO2 productivity in comparison with the ignition in a braid region: The most advantageous ignition point for CO2 productivity is the vortex core region where the mixture strength is high and the flammable mixture spreads rapidly. Once formed, a wrinkled diffusion flame propagates through the multi-stratified mixture, destroying the initially existing vortical structure. In the flamepassed region, the flame extinguishes due to dilution effect by products. In addition, Le number analysis in the vicinity of propagating flame shows flame instability and local extinction.
The vortex filaments in a Kármán vortex street are usually not parallel to the axis of a circular cylinder perpendicular to a uniform flow in a low speed wind tunnel, but incline to the axis of the cylinder. The axial flow to the upstream direction in a vortex was observed by means of flow visualization in each vortex of the Kármán vortex street. The axial flow did not take place when the vortex filaments were parallel to the axis of the cylinder. The axial flow is caused by the pressure gradient in the direction of vortex axis, because the pressure at the center of a vortex increases with diffusion of vorticity of the vortex center and with decrease in the circulation of the vortex as the vortex goes downstream. The axial flow was roughly estimated by using the measured values of circulation and vorticity of a vortex in a Kármán vortex street.
Damping properties of laminated composite beams with interlaminar damping layers are studied analytically. Rayleigh-Ritz method is used to obtain a basic equation of vibration. The displacement field in the thickness direction is assumed to be piecewise linear. The natural frequencies and the damping coefficients are obtained through an complex eigenvalue analysis, where the damping terms of the damping material are considered. Mechanical properties of the damping layers are assumed to be functions of frequency. The calculated results agree well with those of experiment. The damping property of the laminates varies considerably depending on both the viscous and elastic terms of the damping material, which are usually functions of temperature and vibrational frequency. Not only damping properties but also elastic properties of the damping material must be well examined to design the laminated panels with damping sheet(s). The damping coefficients increases with the number of the inserted damping sheets, but the improvement decreases with the number of the damping sheets. The effects of dimensions of the composite beams on damping properties are also investigated parametrically and slenderness ratio of the half wave of the vibrational mode to the beam hight is a dominant factor for the damping property.
Boundary layer separation reduces wing performance. The spanwise pressure gradient generates spanwise flow in boundary layer and increases boundary layer thickness. This thick boundary layer tends to separate easily. Therefore the zero pressure gradient normal to the streamlines could improve wing performance. In this research the effects of wing planform on intersecting angles of streamline and isobar are presented using boundary element method. The wing planforms which have little separation at large lift coefficient are studied.
In the first part A, operational efficiency (WV/P) vs. V of existing WIG vehicles are investigated, although it is limited to ones on which enough data are available for estimating (WV/P). It is found that the domain of WV/P values of WIG are considerably wide. In the second part B, an improved operational efficiency parameter, named “Modified Effective L/D (MELD)” defined as M (WV/P) is proposed. MELD is non-dimensional; M=V/a is an artifitial Mach number, where a is the sonic speed on the standard day at the sea level. MELD has a limiting value of ten and named “Ando's Number.” In the diagram MELD vs. V, better groop of WIG's are rather superior to hovercrafts and hydrofoils as well as helicopters. But, when the payload is used in stead of gross weight, WIG seems to be comparable with passenger car.