Wind tunnel tests were conducted to investigate static roll characteristics of three cranked arrow wings that have different outboard wing sweepback angles to investigate the effect of inboard and outboard vortices upon the wing roll characteristics. Results indicated that breakdown position of leading-edge separation vortex formed on the inboard wing moves upstream as the outboard wing sweepback angle is decreased. A large scale rolling moment hysteresis was observed for the wings with smaller outboard wing sweepback angle, whereas only a small scale hysteresis was observed for higher outboard wing sweepback angle. It was shown that these differences are caused by the different behaviors of inboard vortex breakdown.
A bubble size distribution model has been developed by the author for a cryogenic high-speed cavitating flow of a turbo-pump in a liquid fuel rocket engine. In this model, bubble growth/decay and bubble advection are solved for each class of the bubble size, strictly mass, when there are various mass bubbles in the same calculation region. The above calculations are treated as Eulerian approach with respect to the bubble mass. The numerical results based on this model have agreed with the experimental results as a whole, however, some inconsistency still remained. It is suspected that the model of the bubble growth/decay causes the difference between the numerical and experimental results because heat transfer around the bubble was approximately computed by an analytical solution of unsteady heat transfer based on the elapsed-time from the bubble nucleation. In this paper, a new bubble size distribution model was redeveloped, in which the bubble growth/decay calculations employ a new method combining two rigorous methods, namely, a Rayleigh-Plesset equation for bubble oscillation, and a heat conduction equation in a thermal boundary layer around the bubble to evaluate mass rate of evaporation/condensation.
An innovative defrosting method for precooled turbojet engines are presented, and validated in this study using experimental methods. High speed gas jet was impinged on the cooling tubes of a heat exchanger for the purpose of defrosting. The coolant of the heat exchanger was liquid nitrogen, and whose temperature was 83K. The air flow speed, the air temperature and the air humidity were 1.0m/s, 23ºC and 59%, respectively. The effects of the jet duration, jet intervals and humidity of the jet gas on the heat exchange were assessed. As a result, we found that the presenting defrosting method is valid for the defrosting of the precooler.
In this study, we conduct the numerical simulations of hypervelocity impacts (HVIs) of a projectile on CFRP laminated plate targets by means of two-dimensional axisymmetric SPH method. To simulate the delamination of the laminated composite plate due to the HVIs, an interface modelling technique for mixed-mode delamination is adopted. Additionally, a treatment method for the anisotropy of CFRP composites in the axisymmetric coordinate system is described. Numerical simulation results show good agreement with experimental results in respect of the ballistic limits and the damaged area. Consequently, it is shown that the interface particle technique for modelling the delamination of a laminated composite plate is effective, and we can predict the ballistic limits and the damaged area of laminated composite plate with this technique.
Earth-pointing and polar-orbiting spacecraft, the Advanced Land Observing Satellite (ALOS), has a precision attitude determination system exploiting measurements of a precision star tracker and an inertial reference unit, and controls its attitude, based on the attitude estimates. The star tracker provides the positions and magnitudes of stars. The attitude control system's computer identifies stars which enter the star tracker's FOV and move across it, and applies the extended Kalman filter. The ALOS precision attitude determination system consisting of the star tracker and the onboard computer was tested at the Usuda Deep Space Center in the real night sky environment. The tests using a two-axis motion table demonstrated end-to-end performance, capability, and robustness of the attitude determination system. This paper presents the overview and results of the real sky tests. It also proposes test settings for Earth-pointing spacecraft and a method for alignment error assessment and calibration. Limit of performance due to the test site and configuration are also evaluated.
Composite laminates manufactured using thin-ply prepregs are expected to have superior resistance properties against microcracking compared to those using standard prepregs. In this study, comparative investigations are presented on the microcrack accumulation and gas leakage characteristics of CFRP laminates fabricated using standard and thin-ply prepregs, consisting of high-performance carbon fiber and toughened epoxy, as a fundamental research on the cryogenic composite tanks for future space vehicles. It was shown that laminates using thin-ply prepregs exhibited much higher strain at microcrack initiation compared to those using standard prepregs at room and cryogenic temperatures. In addition, helium gas leak tests using CFRP laminated tubular specimens subjected to quasi-static tension loadings were performed. It was demonstrated that CFRP laminates using thin-ply prepregs have higher gas barrier properties than those using standard prepregs.