野中 聡

“Nose-first entry” flight has been proposed as one of the methods of return flight of a vertical take-off and vertical landing reusable rocket using engine thrust for vertical landing. In this flight method, the engine exhaust jet opposes the free-stream during the turnover maneuver and landing, causing concern that the aerodynamic force acting on the vehicle changes due to a complicated flow field made by the interaction between the exhaust plume and free-stream. A slender-body model that can eject a supersonic jet was studied in a low-speed wind tunnel to characterize the flow. The aerodynamic forces were measured, and the flow pattern on the surface of the model was visualized using the oil-flow technique. The results indicate that the axial force decreases in the low angle-of-attack region, and the rate of change in the axial force is much smaller compared with previous studies in which the jet is ejected from a blunt configuration. The surface flow pattern is also changed by the jet ejection. However, the normal force and pitching moment do not change. Therefore, the influence of the jet strongly depends on the vehicle shape, and the aerodynamic characteristics are restrictive in slender-body shape rockets.

<p>Conventional rockets are faced with several problems such as high launching cost. Therefore, in Japan, a reusable vertical-takeoff-and-vertical-landing (VTVL) rocket vehicle is being developed. This vehicle utilizes nose entry as the return flight system including the attitude change (turnover) due to aerodynamic forces. To safely achieve turnover, it is necessary to reduce the difference between the maximum value and minimum value of C_m (i.e., pitching-moment coefficient). In this study, a delta-wing with vortex flaps (developed for the aircraft industry) is attached to the aft of the vehicle with the expectation of improving the C_m characteristics during the turnover process. Consequently, when the flap deflection angle is 0°, the nose-up C_m can be reduced at forward angles (i.e., AOA 0° - 90°) because vortices generated by the fins result in a nose-down C_m and cancel the nose-up C_m. Moreover, when the flap deflection angle is -30°, the nose-down C_m is enhanced at the backward angles (i.e., AOA 90° - 180°) because the flaps reduce the vortices generated by fins. Hence, setting the flap deflection angle at 0° for the forward angles and -30° for the backward angles reduced the difference between the maximum and minimum values of C_m (i.e., 12% smaller than a conventional model).</p>