Numerical simulations are conducted to investigate the self-ignition and its transition to stable flame-holding in a scramjet combustor with a backward step. A full three dimensional Navier-Stokes equation with a detailed chemical reaction model is solved with varying the location of the fuel injector and the geometry of the combustor. The results show that self-ignition occurs in the boundary layer developed on the injector-side wall. The initial reacting zone expands downstream and toward the recirculation zone behind the step. In the presence of precombustion shock wave (PSW), the reaction in the rear part of the combustor develops into the intensive flame because the PSW much increases the local Damkohler number. On the other hand, the reaction in the recirculation zone has very little effect on the generation of the intensive flame. The self-ignition can be governed by either near-field or far-field phenomena while the transition to the bulk flame is governed by far-field phenomena.
This paper presents an experimental and numerical study of shock wave/turbulent boundary layer interaction induced by rhombic delta fins placed on the side wall of the test section. The experiments were carried out in 80×100mmmm2 supersonic wind tunnel at free stream Mach number of 2.50. Corresponding free stream unit Reynolds number was 3.74×107/m. Five models were used in this study. The fin half apex angles were 12°, 18°, 24° at 30° sweepback angle and for the fin sweepback angles 15°, 45° at 18° half apex angle. Schlieren photographs, oil flow measurements and wall surface static pressure measurements were made. It was found that the upstream influence line runs parallel to the primary separation line and obeys the Reynolds number scaling law. Furthermore, the primary separation angle βs1 can be accounted for by referencing βs1 and β0 to Mach angle μ∞.
In this paper, a numerical method to accurately compute the vortical flows around high-alpha delta wings is proposed. The leading-edge vortex is captured by the adaptive grid refinement method coupled with the vortex-center identification. Effectiveness of this method is evaluated in the vortical flow with vortex breakdown. It is demonstrated that the adaptive grid refinement near the vortex center can significantly improve the accuracy of the vortex breakdown locations, as compared with the experiments. For the relatively small angle of attack case, the adaptive refinement at vortex core improves the surface pressure reasonably. This indicates the importance of the resolution at vortex core for accurate detection of the breakdown. The present numerical method, which combines the adaptive grid refinement method and the vortex core identification, is very effective for such a vortex dominated flow field.
Low power DC arcjets (300W-class) for optical studies of the interior discharge region were developed, combining a slit type or a hole type constrictors (width or diameter: 0.8, 0.3mm) with a two-dimensional nozzle. Following experimental results were obtained. (1) In the occurrence of the unstable low-voltage mode, the anode attachment position of arc column moves upstream, and the cathode spot deviates from the tip of the electrode to the side surface of it. (2) Onen of the causes of the occurrence of the low voltage mode is the aerodynamic instability of arc columu. (3) Two types of anode attachment were noticed, spot type and diffusive type; the former is observed in the neighborhood of constrictor exit, and the latter, in the downstream low-pressure region. (4) In the inlet region of the constrictor, some electrons seem to be drawn radially and flow into the constrictor wall.
The experimental and numerical studies for the effect of expansion length of supersonic nozzle for a combustion-driven CO2 gasdynamic laser facility on the small-signal gain characteristics are presented. Two types of nozzle of Circular-Circular (C-C) and Shock Free (SF) with area ratio of 20 which are able to realize Mach number of 4.7 with vibrationally nonequilibrium flow are used. For C-C nozzle at expansion length of 30mm, maximum value of the smallsignal gain coefficient is measured as 0.5m-1, and also for SF nozzle at expansion length of 45, 30 and 20mm they are 0.2 to 0.3m-1. It is shown that the higher small-signal gain coefficient is obtained at shorter nozzle expansion length, which suggests generation of a laser output extraction over the threshold value.
Operations under single pilot instrument flight rules for general aviation aircraft are known to be one of the most demanding pilot tasks. Pilot workload measurements using a PC-based flight simulator have been done to investigate pilot skills and the pilot workload. A pilot workload evaluation method has been established that is partly based on the time and motion studies and that mainly concentrates on the pilot's information processing. The time-record of pilot's eye movement has been used for the evaluation. Pilots who have different flight experiences attended the tests. Comparisons between the results by experienced pilots and those by novice pilots were made. It was shown that the relatively correct pilot workload has been evaluated by the present method. Results for the VOR tracking flight showed that the workload of the experienced pilots increases only when the airplane attitude has been changed, while results of the novice pilots show high workload continuously during the whole flight.