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.

“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>

<p>It is known that aerodynamic characteristics of a slender body vary substantially at high angles-of-attack (AoAs), and then, will have strong impacts on its flight. For, example, the yaw force makes flight unstable. In this study, we investigated the relation between the yaw force and the configuration, and details of flowfield around the slender-bodied-vehicle numerically. The configuration consisting of “nose cone” and “square aftbody” parts was employed as the baseline, and then, compared with other three configurations having different fineness ratios. According to our computed results, in the case of 50 degrees of AoA, the longer the model became, the more asymmetry appeared: yaw force and asymmetry were found to be attributed not only to the length of the body, but also to the nose bluntness. On the contrary, in the case of 140 degrees, the shorter the model became, the more asymmetry appeared. Furthermore, the large nose bluntness increased C_Y. Interestingly, this trend is totally opposite to that observed at 50 degrees. It had been considered that the large nose bluntness and the small fineness ratio can reduce asymmetry and C_Y, however, this study showed that it is not true in the case over 90 degrees, due to complex wake flow structure discovered in the present numerical simulations.</p>

<p>The development of a fully reusable vertical-takeoff-and-vertical-landing (VTVL) rocket is indispensable for reducing space transportation costs. However, there are many technical issues associated with such vehicles, such as turnover maneuvers during return flight where the pitching moment plays a key role. It is known that aerodynamic characteristics can be controlled by installing aerodynamic devices, but the relationship between the aerodynamic characteristics and the flowfields has not been explored. To clarify this relationship using computational fluid dynamics (CFD), we investigated these flowfields and aerodynamic characteristics, in the case where we install such devices (fins) in the nose part of a reusable rocket. We found that vortices form downstream of the aerodynamic devices. For angles of attack between 0 and 90 degrees (in which the fins are located in the upstream portion), these vortices significantly affect the surface pressure on the rocket and increase the pitching moment. On the other hand, for AOAs between 90 to 180 degrees (in which the fins are in the downstream portion), the effect of these vortices on the on-surface pressure is negligible, and only vortices formed near the surface of the fins increase the pitching moment.</p>

<p>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 °.</p>

<p>In this paper, anomaly detection that is configured as a combination of state observer and Mahalanobis-Taguchi (MT) method is proposed for real time fault detection of rapid and dynamic phenomena such as rocket engine operation. Real time anomaly detecting is recognized as one of the most important elements to realize advanced reusable space transportation system. Conventionally, bottom-up type anomaly detecting logic based on failure mode and effect analysis (FMEA) is usually used for this purpose, however, it requires large amount of time and labor. The proposed method can improve this process. In the present method, error values between calculated ones through rocket engine simulator constructed on autoregressive moving average model and extended Kalman filter (EKF) and measured ones are standardized with existing normal operation data of the rocket engine so as to compute Mahalanobis' distance, which expresses degree of anomaly. We performed engine hot firing tests in simulated anomaly conditions. The obtained data was processed with the present method, and the simulated anomaly in the tests was detected as expected.</p>