The purpose of this study is to validate the utility of a forward-swept wing in significant reducing the acoustic level of the sonic boom during a supersonic cruise. This was achieved by investigating the aerodynamic performance of wings with different leading edge angles. A total of 13 wing-body-engine nacelle configurations were defined with varying outer wing planforms for a supersonic business jet model. The resulting aerodynamic drag was evaluated using the three-dimensional compressible Euler equation, and the acoustic level of the sonic boom was evaluated using the augmented Burgers equation. The calculated results for supersonic cruise conditions indicated that the maximum acoustic level of the sonic boom of a forward-swept wing was approximately 4.8 PLdB lower than that of the original backward-swept wing. Furthermore, a forward-swept wing reduced the aerodynamic drag as effectively as a backward-swept wing during supersonic cruising. The sonic boom signature at the ground level indicated that forward-sweeping of the wing caused obvious multi-peaks on the bottom peak of the trailing sonic boom, which demonstrated that the forward-swept wing could reduce the intensity of trailing sonic boom.
Impulsive vibration during rocket launch has the risk of causing indentations inside the bearings of reaction wheel mounted on a satellite. The indentations induce the vibration disturbance during the bearing rotation, which is harmful to precision equipment. In order to investigate the mechanism of the indentation formation, we carried out the experiments and finite element simulation for simplified reaction wheel. Based on the results of simulation, we estimated the depth of plastic deformation and wear using Palmgren’s formula and PV value, respectively. The indentation depth of simulation shows good agreements with that of experiment. The results also show that the wear between balls and rings is dominant factor of indentation formation, as compared with the plastic deformation. The amount of wear is greatly affected by the location of ball. In the location where the contact direction between ring and ball is parallel to the vibration direction, contact pressure contributes the wear as compared with slip velocity. Inversely, in the location where the contact direction is perpendicular to the vibration direction, the slip velocity contributes the wear and induces the larger wear region.