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Acoustic simulation of hot jets issuing from a rectangular hypersonic nozzle was carried out. The aim of this study is, even though qualitative to some extent, to establish a method capable of predicting the acoustic characteristics of the high-temperature and high-velocity jets issuing from the realistic hypersonic nozzle having a complicated geometry. Two kinds of test nozzles, 2.4% scaled model with afterburner for hot jet experiments and 1.0% scaled model for cold-air/helium mixture jet experiments, were manufactured and tested. By using a high-enthalpy wind-tunnel plant, acoustic characteristics of the hot jets issuing from the rectangular hypersonic nozzle for several representative but realistic high-temperature and high-velocity jet conditions were obtained. At the same time, by using a small anechoic chamber, the acoustic characteristics of the hot jets were duplicated using cold-air/helium mixture jets having the same velocities. Although we have to pay attention to some noted exceptions, the di...

Flames are affected by external electric fields because they contain ions and electrons. The movement of ions and electrons affects the external electric field owing to their charge. In this context, this paper discusses the change in the electric field on the basis of experimental results obtained at different electrode distances. Employing one-dimensional (1D) steady-state analysis, we assume that if the electric field is changed spatially, the effect of the electric field on combustion behavior is aligned with V2/L3, where V is the applied voltage between the electrodes and L is the distance between the electrodes. Because a flame deforms to a cathode owing to electric body force in an electric field, the change in the flame shape of burning ethanol droplets observed in a vertical DC electric field and the electric current during combustion are measured as flame characteristics. The results reveal that applied electric voltage exists where the flame becomes vertically symmetrical to balance the buoyancy due to the electric body force. The relationship between m and n of Vm/Ln for flame symmetry is around n/m = 1.5. On the basis of these results, all experimental results for different electrode distances are rearranged with eV2/L3, which is a representative electric body force, and it is proved that the use of parameter eV2/L is effective. These results indicate that the change in the electric field due to the existence of a flame should be considered when examining the effect of an external electric field on combustion behavior.

Pre-cooled turbojet engine is investigated to realize Mach 5 class hypersonic transport aircraft. The engine has been demonstrated under sea level static and Mach 2 flight conditions using hydrogen as fuel. In this study, Mach 4 propulsion wind tunnel test is performed and the performance of air intake, pre-cooler, core engine and exhaust nozzle are obtained. Liquid nitrogen is supplied to the pre-cooler as a coolant in place of liquid hydrogen. Gaseous hydrogen is supplied to the main burner to drive the turbine with the combustion gas. A protective screen is placed in front of the pre-cooler to prevent damages of it from high-speed particles. Bypass door is placed in front of the core engine to start the mixed compression air intake at low speed operation of the core engine. As a result, the engine performance data is obtained without any damage of pre-cooler. Air intake is started by the effect of bypass door at low speed operation of the core engine.

Pre-cooled turbojet engine is investigated to realize Mach 5 class hypersonic transport aircraft. The engine has been demonstrated under sea level static and Mach 2 flight conditions using hydrogen as fuel. Presently, Mach 5 propulsion wind tunnel test using liquid hydrogen is planned and the engine components such as pre-cooler, core engine, afterburner and exhaust nozzle are under development. The engine components were tested under Mach 4 simulating condition by connecting the pre-cooler inlet to an air supply facility. The engine was tested in a propulsion wind tunnel with Mach 4 flight condition. Liquid nitrogen was supplied to the pre-cooler as a coolant in place of liquid hydrogen. Gaseous hydrogen was supplied to the main burner to drive the turbine with the combustion gas. As a result, high temperature structure and cooling system was proved to endure Mach 4 high temperature airstream. Wind-mill starting sequence of the core engine under Mach 4 flight condition was confirmed. Gross thrust of the core engine was obtained as an initial evaluation of elemental performance.

Silicon mounds fabricated on the Si(1 0 0)2×1 surface by a tip of a scanning tunneling microscope (STM) have been observed by STM at substrate temperature of 770 K. The shape of the mound is a quadrangular pyramid with facets of regular array of steps with double layer height. For all the step, the dimer rows are perpendicular to the step edges, so called the D B step. Just after the fabrication, the pyramid begins to decay immediately layer-by-layer. During decay, the D B steps move scarcely, but only the S B steps at the bottom layer move due to attachment and detachment of atoms which are detached from the upper layers. For a single layer mound, the aspect ratio of the mound oscillates between about 2.5 and 1.5.