Typical space transportation vehicles have various asymmetric protuberant devices on their surfaces, such as cable ducts and side jet motors. Such protuberances, when arranged asymmetrically with respect to the vehicle axis, are known to cause asymmetric vortices that produce side force. In this study, to understand effects of side force and its associated flow fields, both wind tunnel tests and numerical calculations for a slender body with an asymmetric protuberance were conducted at a wind speed of Mach 1.5. The results of computed aerodynamic coefficients are in good agreement with the experimental results and detailed flow structures are provided. In particular, the results revealed that side force was generated by two factors. It linearly increased as vortices detached from the body and nonlinearly increased based on the effects of secondary vortex scale as the angle of attack increased. Additionally, the axial position and azimuthal angle (angle along the circumferential direction around the body axis) of the protuberance strongly influenced side force characteristics. First, the side force was significantly higher when the protuberance was installed in a forward axial position. Second, when the protuberance was installed on the leeward side of the slender body (upper side), the side force increased with the angle of attack. These results are not limited to the presented configuration and can be applied to other rocket designs for cost reduction and safety enhancement.

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Most of flight vehicles have various protuberant devices on their surfaces, but asymmetry in their positioning with respect to the body axis can affect aerodynamic characteristics of vehicles, particularly roll moment. Thus, it is important in rocket development to clarify the effects of the protuberances on the vehicle aerodynamic characteristics. In this study, as a basic research, we systematically investigated such effects using CFD, by changing the positions of a protuberance. As a result, the roll moment increased nearly linearly with angle of attack (=α), but its trend was different in protuberance locations, particularly when arranged near the center-of-gravity. In positioning there at α = 20°, the wake vortex center moved farther away from protuberance compared with α = 15°, then the pressure decline at its wake side was suppressed, and thus, the pressure difference between its upstream and downstream sides became smaller. As a consequence, the roll moment did not arise linearly, but decreased at α = 20°.

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