Recently, various studies of Micro Air Vehicle (MAV) and Unmanned Air Vehicle (UAV) have been reported from wide range points of view. The aim of this study is researching the aerodynamic improvement of delta wing in low Reynold's number region to develop an applicative these air vehicle. Various configurations of Leading Edge Flap (LEF) are used to enhance the aerodynamic characteristics in the delta wing. The fluid force measurement by six component load cell and PIV analysis are performed as the experimental method. The relations between the aerodynamical effects of the LEFs and the vortex behavior around the models are demonstrated. It is shown that the combination type LEF consisting of upward and downward deflected short span LEFs, is effectual device in the angle of attack region where lift curve slope rapidly decreases after stall.
A pulsed-laser-driven MHD electrical power generation has been demonstrated experimentally for the first time. High temperature argon gas plasma flow is induced by an irradiation of pulsed CO2 laser, and electric power has been extracted from the MHD power generator, although the output level remains still quite low. The time-dependent two-dimensional numerical simulation would explain the behavior of MHD fluid flow and the variation of power output partially.
The objective of this study is to explore the effects of incident shock waves on combustion downstream of a cavity flameholder. The images of flame chemiluminescence showed that the flame looks extinguished downstream of an incident shock wave, as well as OH-PLIF measurements indicated higher OH concentration upstream of the incident shock wave, while lower OH concentration downstream of the incident shock wave. The results of two-dimensional numerical simulations for reacting flows showed that the incident shock wave generates a strong recirculation zone and reverse flows, and the main flow curved around the zone, corresponding well to the flame structure seen by experiments. In addition, it was found that about 90% of the injected H2 was converted to H2O at the rear edge of the calculated wall domain when an incident shock wave was introduced, which means that cavity-stabilized flames is not extinguished by the incident shock wave but burnt out there, thus the fuel was almost fully consumed. That is to say, the incident shock wave enhances chemical reactions because the generated recirculation zone and low speed region increases residence time and increased turbulent kinetic energy enhances the mixing.
A new lightweight ablator was fabricated by the infiltration of a polyimide resin into a porous carbon material having three-dimensional network and open cell structure. In order to evaluate the performance of the ablator, the thermal response and recession resistance were evaluated using an arc wind tunnel. These properties were discussed from the viewpoint of the cell sizes of porous carbon material. With a decrease in the cell size, internal temperature of the ablator became lower. Microstructural observations revealed that the three-dimensional network structure of the ablator, which originates from the porous carbon preform, was maintained after the heating tests. Consequently, the recession resistance was better than those of existing ablators fabricated from carbon-fiber-based preform.
A natural laminar flow wing was designed using a computational-fluid-dynamics-based inverse design method of supersonic transport at high-Reynolds number condition to reduce the friction drag of a large supersonic commercial transport. Design of the higher Reynolds number condition is more difficult than the lower Reynolds number condition because a target pressure distribution that can achieve natural laminar flow has steeper pressure gradients at the leading edge than a low Reynolds number condition. This study improved the conventional natural laminar flow design method by inverse design starting from a low-Reynolds number condition design, variable smoothing strength, the modified trailing edge closing method, and so on. The improved inverse design method was applied to a large supersonic transport with 300 passengers at the condition of Mach 2.0 and high Reynolds number of approximately 126 million based on the mean aerodynamic chord. The results and the effects of the improved natural laminar flow design are described here in.
Measurements of flow field over a NACA0012 airfoil were performed with hot-wire anemometer at three cases of Reynolds number of 10,000, 30,000 and 50,000. We focus our attention on characteristics of both laminar separation region and separation bubble on the airfoil in order to find the characteristics of the flow field responsible for peculiar aerodynamic nature of the airfoil in low Reynolds number regions. This paper deals with separation and reattachment of the boundary layer on the airfoil to make certain the conclusions of our previous papers. By results of velocity distributions, laminar separation region is confirmed in low angle of attack regions, separation bubble is also confirmed on the airfoil as increasing of angle of attack. Shape factor of $H$ and second shape factor of $K$ are calculated by boundary layer profiles and are applied criterions of boundary layer separation, separation and reattachment points can be estimated on the airfoil. We find overviews of flow field phenomena involving a separation bubble in low Reynolds number regions.
We propose thrust vector management by correctly positioning the thruster on a spacecraft by thrust vector measurement to decrease unwanted torque of thrust vector misalignment. A ground test was performed to measure 2-dimensional ion current distribution of 10W-class miniature ion thruster by electrostatic probe. The thrust vector measurement test showed that the thrust vector inclining angle was 1.4º from the geometrically symmetric axis of the thruster. The thruster was positioned on the first interplanetary micro-spacecraft: PROCYON after redesigning thruster bracket. Thrust vector estimation in the initial on-orbit operation of 6.5 hours showed that thrust vector passes through within 5mm of the PROCYON's center of gravity.
The burning rates of small sized Boron Potassium Nitrate (BKNO3) pellets (3.2-mm-dia., B:KNO3: binder = 28:70:2) under low pressures were experimentally measured; they increased with pressure (r = 71.1p0.589[mm], p[MPa]) at an ambient pressure higher than 5 kPa and exhibited little dependence on pressure (r = 3.0±0.5mm/s) at an ambient pressure lower than 5 kPa. The measured pressure increase after reaction becomes smaller under 1 kPa and the photographs taken by a high-speed camera showed unreacted particle emissions at 0.2kPa. These results suggest that the reaction of BKNO3 at low pressures takes place in condensed phase. From thrust stand measurement, the pressure working on the combustion surface is estimated to be 1.2kPa, which implies that the dependence of burning rates on ambient pressure vanishes under around 1kPa.