Studies on Aerodynamic Characteristics of Next Generation's Vertical Take-off and Landing Reusable Rocket in Relation to Safety at Landing

垂直起降火箭是解决低成本、可重复使用空间运输系统需求的解决方案之一。这种飞行器的垂直软着陆是通过火箭在地面附近的反燃来实现的。本文对火箭喷管射流的地面效应所引起的气动力进行了实验和数值研究。主要结论如下：1。当测量到的从地面到车辆基座的高度较小时，基座压力减小，向下的力作用在车身上。它随着海拔的降低而增加。在非常低的高度，它变得比喷嘴推力大，飞行器被拉向地面。当高度较高时，地面上的撞击射流诱导出“吸力型”流型，将周围空气吸入基底下方区域，基底压力略有降低。当高度较低时，流型转变为“涡型”，射流周围形成涡环，基压明显降低。通过修改车座外缘和磨粗地面表面可以减小向下的力。在多喷嘴的情况下，由于喷嘴喷射的相互作用，向下的力变弱。在塞式喷嘴的情况下，向下的力比钟形喷嘴的情况下要小，因为塞底部的压力由于地面效应而增加。为了保证车辆的安全，不仅需要在着陆阶段对车辆进行仔细的控制，而且需要通过第3项指出的方法减小向下的力。

A vertical take-off and landing rocket is one of the solutions to the need for low cost, reusable space transportation system. Vertical soft landing of such vehicle is achieved by retro-burn of the rocket near the ground. In this study, the aerodynamic force induced by the ground effect of the jet from the rocket nozzle is experimentally and numerically investigated. The major conclusions are as follows :1. When the altitude measured from the ground to the vehicle base is small, the base pressure decreases and the downward force acts on the body. It increases with the decrease in the altitude. At very low altitude, it becomes larger than the nozzle thrust and the vehicle is drawn toward the ground.2. When the altitude is relatively high, the impinging jet upon the ground induces the flow pattern classified into the "suction mode", where the ambient air is sucked into the region under the base and the base pressure is slightly decreased. When the altitude is low, the flow pattern is changed into the "vortex mode", where a vortex ring is generated around the jet and the base pressure is significantly reduced there.3. The downward force can be reduced by modifying the outer edge of the vehicle base and roughening the ground surface.4. In the case of multi-nozzles, the downward force becomes weak due to interaction of the jets from the nozzles.5. In the case of the plug nozzle, the downward force is smaller than in the case of the bell nozzle, since the pressure at the plug base increases due to the ground effect.6. To ensure vehicle safety, not only careful control of the vehicle during the landing phase but also reduction in the downward force by the methods as pointed out in item 3 are necessary.