Flutter Analysis of Balloon-Based Operation Vehicle for Precooled Turbojet Engine Demonstration

Abstract

‡§ ** In This study, three-dimensional aeroelastic phenomena of a balloon-based operation vehicle (BOV) currently being developed by JAXA are numerically simulated. The finite element method (FEM) is used for modal vibration analysis. The 3D solid structure model of the BOV tail wing is constructed, and then the vibration modes are mapped to 2D isoparametric shell elements for the efficient fluid-structure coupling. Some results are compared with the flutter characteristics of “NAL wing” which has similar planform with BOV wing and is well used for a test case for the flutter simulations. The obtained flutter boundary showed that the BOV tail wing and main wing have enough safety margins for the flutter in the current flight condition. I. Introduction EVERAL phenomena observed in microgravity environments have not been fully clarified because of large differences between microgravity and the earth’s gravity; the elucidation of these phenomena is considered important from the viewpoints of both scientific interest and the development of potential applications to engineering and medicine. A microgravity environment can be realized for long durations (e.g., space platforms and space satellites) or for durations as short as 20 seconds or less (e.g., aircrafts and fall towers). However, problems remain from the viewpoint of cost for the former and of duration and residual gravity for the latter. The Japan Aerospace Exploration Agency (JAXA) has begun a development project for a Balloon-based Operation Vehicle (BOV) that uses a high-altitude balloon as a means to achieve a microgravity environment for about 1 minute at a low cost. We drop this experiment vehicle freely after lifting it up to an altitude of about 40 km with a high-altitude balloon, and we then perform microgravity experiments using an experiment module stored in the vehicle. Figure 1 shows the initial examination chart of the vehicle. To counterbalance the influence of air resistance during the vehicle's descent, a gas jet is installed in the vehicle, and the relative position is measured with the laser displacement sensor and controlled for the experiment module in the vehicle so as not to collide with an outside capsule and to allow the vehicle to fall freely. The vehicle has four fully movable wedge-shaped tails, and it splashes down after deceleration with a parachute and is then retrieved. Furthermore, a plan to install an airbreathing engine (precooled turbojet engine) on the vehicle and to execute an engine operation examination under real-flight conditions also underway. Details of this BOV project can be obtained from earlier studies. 1-2