藤井 孝藏

The accurate evaluation of the ground reflection effect is of importance for acoustic measurement conducted during static-firing tests of rocket motors. The effectiveness of existing acoustic impedance models was examined by comparing experimental data collected from acoustically hard surfaces. Through these comparisons and the subsequent evaluation of the effect of meteorological conditions, it was confirmed that the existing impedance models are not suitable for the evaluation of long-distance propagation over a hard surface, which corresponds to the far-field conditions in the present static-firing tests of solid rocket motors. A new acoustic impedance model is proposed in this paper. Comparisons of the acoustic measurement data indicated that the new model is effective for both near- and far-field propagation of acoustic waves. The proposed model was applied to acoustic data collected during static-firing tests of solid rocket motors assuming distributed acoustic sources along the exhaust jet axis in order to remove the ground reflection effect.

Evaluation of ground effect is important for acoustic measurement in static-firing tests on rocket motors. The effectiveness of existing acoustic impedance models is examined by comparing with some experimental results. Through the comparison and evaluation of effect of meteorological condition, it is confirmed that the existing impedance models are unsatisfactory for the evaluation of long distance propagation over a hard surface, which corresponds to the far field condition in the present static-firing tests of rocket motors. In this study, a new acoustic impedance model is proposed. From the comparison with the existing acoustic measurement data, it is shown that the new model is effective for both of near and far field propagation. The proposed model is applied to acoustic data measured in the static-firing tests of solid rocket motors, assuming distributed acoustic sources along the exhaust jet axis.

The dielectric barrier electric discharge plasma actuator is expected as a new technology which can make the design of an aerofoil etc. unnecessary. The boundary layer control might be able to be performed by induced velocity in the boundary layer as an effect of the dielectric substance barrier electrical discharge plasma actuator. Moreover, it also turns out that the control effectiveness increases by repeating ON and OFF of the applied voltage, which is called burst. But, the control mechanism is unknown. In this study, separation control on an airfoil by a plasma actuator was performed, and its control effectiveness was evaluated. The result showed a possibility to change the control effectiveness with the burst frequency mainly.

Aerodynamic characteristics of a reusable observation vehicle are computationally investigated under subsonic and supersonic flight conditions as a preliminary study for the concept design using a design exploration method and a light CFD tool. The results show that the simulations with a coarse grid can accurately estimate the aerodynamic characteristics like axial force coefficient and the lift to drag ratio. The results of the aerodynamic shape exploration indicate tradeoff information among objective functions, and the correlation between design variables and objective functions. The preliminary knowledge for the aerodynamic shape design is obtaind.