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

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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.