Visualization and PIV measurements were conducted in a towing air-chamber for wake vortices behind a paraboloidal-nose cylinder at high angles of attack. The evolution of the wake was then measured by a particle image velocimetry (PIV) using cross-sectional and longitudinal cuts which were produced by the sheet illumination of the Nd:YAG laser. To visualize the three-dimensional evolution of flow in the vicinity of wall, we employed a titanium tetrachloride (TiCl4). It was predicted by the PIV study that serial vortex loops with almost constant spacing appear around the main vortex.
A parametric study on configurations of a boundary-layer diverter for supersonic propulsion system was conducted using CFD simulation to examine those effects on the flow field and the performances of the diverter. The performances were evaluated in terms of its aerodynamic drag and ingestion of the boundary-layer on the airframe surface. Height, width, and apex angle of the diverter were used as the parameters. It is found that narrow width yields good performances in terms of the drag as well as the boundary-layer ingestion. The effect of height and apex angle exhibits trade-off between aerodynamic drag and ingesting the boundary-layer. In the design process of diverter, firstly, the width of diverter should be set to minimum value, then, the apex angle and the height should be optimized.
Three wind tunnel tests for flutter have been conducted under the development of the National Experimental Airplane for Supersonic Transport (NEXST-1) of JAXA launched in 2005. Three kinds of flutter were investigated by using three different wind tunnel models at that time. Discussion of this paper is mostly on the one for a main wing model. The planform of the NEXST-1 wing is a cranked arrow having warp in the out of plane direction. For flutter, the model showed the so called transonic dip of which bottom speed was at Mach 1.02. It was also subjected to limit cycle oscillation (LCO) in the transonic regime. The flutter was dominantly the bending of the out board wing. In the design stage of the NEXST-1, a 20% reduction was anticipated for the transonic regime by the flutter analysis with the linear aerodynamic theory. The wind tunnel experiment resulted in 21% lower in the flutter speed that was slightly higher than the assumption. The NEXST-1 aircraft was launched in the piggy back style by the solid rocket booster. Therefore, the flutter was also investigated for this launching configuration. The flutter speed reduction in this case was 27%, which was larger than that for a sole airframe. As a consequence, the design methodology for transonic flutter is thought to be confirmed for supersonic flight vehicles.
A sensitivity analysis was carried out using a three-dimensional grid erosion analysis code to understand the effect of doubly charged ions on the erosion of an ion acceleration grid. In the preliminary analysis, it was found that the neutral flux value estimated by assuming all the ions to be singly charged has significant errors when the doubly charged ion fraction is non-negligible. Calculations were conducted for the μ10 EM1 ion acceleration grid system, varying the doubly charged ion fraction (0, 0.1, and 0.2), and the experimental and simulation results of the acceleration grid current and acceleration grid mass loss were compared. In the case of doubly charged ion fractions of 0.1 and 0.2, which are similar to the experimental condition, the simulation results were in good quantitative agreement with the experimental data. Calculation results showed that when the doubly charged ion fraction was varied from 0.1 to 0 (0.2), the acceleration grid current and acceleration grid mass loss changed by -14% (+9.5%) and -18% (+32%), respectively. Electron backstreaming was also found to vary with the doubly charged ion fraction; it occurred 14% slower (12% faster) when the doubly charged ion fraction was varied from 0.1 to 0 (0.2). The structural failure of the deceleration grid was less sensitive than electron backstreaming; the deceleration grid eroded 8.3% slower (8.6% faster) when the doubly charged ion fraction was varied from 0.1 to 0 (0.2).