Control of a cavity tone has been done using triangle projections attached at an exit of two-dimensional jet. Experimental results of sound pressure level show that the projections obviously reduce both total sound pressure level and sound level of the dominant frequency of the cavity tone. The sound dumping effect is increasing with increasing number and/or height of projections though this dumping effect saturates with the certain number of projections at the nearly same sound level as that in the wall jet case. The spanwise distribution of pressure fluctuation at the downstream cavity edge has the minima at the right downstream position of the projections and at the other spanwise positions pressure fluctuation is homogeneously reduced. This result suggests that the mechanism of sound dumping is not only breaking two-dimensionality of flows.
The experiments of a delta wing’s spin phenomena were conducted at the low speed wind tunnel of Nagoya University with its exit test section inclined vertically. The spin rate of the delta wing in the free rotation mode was measured as well as surface pressure distributions on the spinning delta wing. At low angles of attack the spin rate increases with sideslip angle, whereas near the stall angle, it decreases. At low angles of attack, when the wing has a sideslip angle, the upper surface pressures of the windward wing-half become lower than those of the leeward wing-half, while near the stall angle the latter become lower than the former. These asymmetric pressure distributions cause the spinning motion of the delta wing. It is evident from these pressure distributions and flow visualizations that a leading edge separation vortex makes an important role in spin phenomena of the delta wing. It is also found that at the equilibrium spin rate, the spanwise distribution of the pressure difference between upper and lower surfaces, ΔCp , shows a nearly symmetric pattern regarding the wing centerline.
The staged combustion hybrid rocket is under development by our research group since 1999. This hybrid rocket engine consists of two combustion chambers. The primary combustion chamber is the fuel tank itself filled with granular solid fuels. The fuel rich gas generated by the first stage combustion flows into the secondary combustion chamber, which is located in the bottom of the primary combustion chamber. The additional oxidizer is injected to the secondary combustion chamber in order to attain an optimal specific impulse by completing combustion. There are two types of the primary combustion. One is nicknamed as the incinerator type; the other is called the multi-grain type. This new type engine is featured with a wide range throttling capability and an extensive freedom in selecting the fuel material. This paper deals with the incinerator type. Presented are preliminary experiments as well as the systems description.
In order to estimate the wind tunnel data uncertainty, it is necessary to consider the error propagation caused by the tunnel flow quality. At the NAL 1.27 m hypersonic wind tunnel, multi point calibration tests of the flow field and 6-component force tests of a winged vehicle model were conducted to estimate uncertainties of aerodynamic coefficients. A statistical assessment of Mach number distributions in the uniform core flow gave us an uncertainty of dynamic pressure. Contributions of each uncertainty to the result uncertainties were examined and the large contributions of the dynamic pressure uncertainty were found. These estimated uncertainties were validated by repeat test results and comparisons of the same model test results obtained in another wind tunnel at the same test condition. This uncertainty estimation method is appropriate for hypersonic wind tunnel testing since the model existence gives little effect on the upstream flow.
Progress in materials technology has produced a much more durable synthetic fabric envelope for the non-rigid airship. Flexible materials are required to form airship envelopes, ballonets, load curtains, gas bags and covering rigid structures. Polybenzoxazole fiber (Zylon) and polyalirate fiber (Vectran) show high specific tensile strength, so that we developed membrane using these high specific tensile strength fibers as a load carrier. The main material developed is a Zylon or Vectran load carrier sealed internally with a polyurethane bonded inner gas retention film (EVOH). The external surface provides weather protecting with, for instance, a titanium oxide integrated polyurethane or Tedlar film. The mechanical test results show that tensile strength 1,000 N/cm is attained with weight less than 230g/m2. In addition to the mechanical properties, temperature dependence of the joint strength and solar absorptivity and emissivity of the surface are measured.
An index that well reflects the difficulty of ground deployment testing is the ratio of gravity force to deployment force. The object of this study is to quantitatively clarify the relationship between the difficulty index and the accuracy with which deployment force can be evaluated. We perform ground deployment tests using a simple planar truss in micro gravity and gravity environments. Ground tests in which the difficulty index value of the planar truss is increased are also performed. By comparing the experimental and analysis results, we quantitatively evaluate the difficulty index and the accuracy with which the deployment force can be estimated from ground testing. We introduce an index that indicates the size limit of deployable structures up to which ground test evaluations remain accurate.
The optimal fuel injector shape for a supersonic combustor is investigated in terms of rapid mixing of fuel jet and supersonic airstream. A Multi-Objective Genetic Algorithm (MOGA) has been applied to discover the optimal fuel injector shape, and two goals of the optimization are adopted. One is to maximize the jet core height, and the other is to minimize the total pressure loss. The algorithm works well, and the characteristics of the optimized shapes for the fuel injector are understood. The effects of the fuel injector shape, which is derived from the statistical process of the optimized shape, are numerically investigated on the jet core height and total pressure loss.
ETS-VII is a test satellite to perform in-orbit demonstration of autonomous rendezvous docking (RVD) technology, which will be necessary for advanced space activities in the early 21st century. ETS-VII performed three RVD experiment flights, and verified all technical items. Three types of guidance and control method were used in three approach phases; C-W guidance law in relative approach phase, reference trajectory guidance law in final approach phase, and relative 6 degree of freedom control in docking phase respectively. We present ETS-VII RVD guidance and control system, and evaluation of its on-orbit performance in this paper. Its performance was better than requirement in each phases.
Wrinkling phenomena of membrane, which include highly geometrical nonlinearity, are analyzed for future large space structures with membranes. Using mixed interpolation of tensorial components (MITC) shell elements, out-of-plane properties of wrinkled membrane, which could not obtained by the conventional tension field theory, are investigated. Various characteristics of a circular membrane with a center rotation hub are clarified; the effects of initial stress, membrane thickness and structural features on its wrinkled region are shown, and the number of wrinkles and out-of-plane deformation are presented. Difference of wrinkled region from these obtained by the tension field theory are also discussed.