Satoshi Nonaka

JAXA has been planning to adopt a nose-entry flight method, in which a glide flight is followed by a turnover maneuver, as a return flight method for vertical-takeoff and vertical-landing rockets. To clarify the aerodynamic characteristics during the turnover maneuver, both (conventional) static calculations with fixed angles of attack and (computationally challenging) dynamic calculations by continuously changing the angles of attack by [Formula: see text], corresponding to 1.0% of the freestream velocity at the nose were performed. The numerical results were verified and validated by corresponding experimental results. Then, these aerodynamic coefficients and flowfields were compared directly to investigate the turnover effects. The results revealed that the leeward vortex structures and aerodynamic coefficients at [Formula: see text] differ by 48% (pitching moment coefficient). Conversely, at [Formula: see text], the aerodynamic coefficients only differ by 4.8% (pitching moment coefficient), although a difference was observed in the base vortices. In summary, through the dynamic simulation, an important aerodynamic feature of the maneuvering vehicle was discovered, in which the flowfield at an earlier attitude significantly influenced that at the subsequent time; this cannot be reproduced or revealed by static simulations in which different angle-of-attack cases are conducted separately.

The presence of protuberances can create an asymmetric flowfield, which contributes to side forces in slender-bodied launch vehicles. In this study, we conduct numerical calculations using a supercomputer at Japan Aerospace Exploration Agency (JAXA) on a slender body with a different-sized protuberance at Mach 1.5 to systematically determine the aerodynamic effects of the protuberance size. The protuberance size is varied in its height and width. According to the results, it is demonstrated that the side force significantly increases when the height of the protuberance increases. This is because, the higher the protuberance, the farther the wake vortex produced by the protuberance moved away from the body. Consequently, the flow asymmetry between the protuberance side and clean side is augmented, and the side force increases. In contrast, the side force is almost constant when only the width of the protuberance is changed. The results of this study indicate that when attaching the protuberance to the vehicles the height of the protuberance should be lowered, and the width of the protuberance should be increased to secure the volume of the protuberance and reduce the increase in side force.