飞行器上层大气层空气动力特性探讨

On Characteristics of Upper Atmosphere Aerodynamics of Flying Vehicles

针对近地轨道飞行器所面临的上层大气层(100~300 km)空气动力学问题,对几类典型航天器构型的上层大气层气动力特性进行了分析,给出了典型气动布局在该空域的气动力基本规律,取得了对上层大气层气动力关键影响因素的初步认识.在上层大气层,飞行器的绕流属于自由分子流状态.研究发现,气体分子与不同材质物面的相互作用反映出截然不同的升力和阻力特性.对于1 m2气动受力面的飞行器,在100~200 km轨道高度存在大于1 mN的气动力,在接近300 km轨道高度时受到的气动力则远小于1 mN.在一般条件下,飞行器的升阻比小于1.但是,当物面适应系数约为0.2时,在100~200 km轨道高度存在升阻比大于1的状态,这一特点体现了上层大气层气动力学的基本特性.据此认为,100~200 km是气动力可利用的飞行空域,在此空域开展上层大气层空气动力学研究,对于未来发展上层大气层飞行器意义重大.

In order to gain the understanding on aerodynamics of flying vehicles in the upper atmosphere(100~300 km),aerodynamic characteristics of typical aerospace vehicles in this space have been analyzed,and a preliminary understanding on the key factors of the upper atmosphere aerodynamics has been obtained.The gas flow over objects in the upper atmosphere falls into the free-molecular flow regime due to its extremely rarefied air stream.The aerodynamic force of a typical vehicle with an upstream flow deploying area of 1 m2 is at the order of 1 mN in the range of altitudes from 100 to 200 km,and it is much smaller than 1 mN at altitudes close to 300 km.Generally,the lift-to-drag ratio of space vehicles flying in the upper atmosphere is smaller than 1.However,it can be augmented by decreasing the accommodation coefficient in gas-surface-interaction.In exploration calculation,the lift-to-drag ratio can be larger than 1 when the accommodation coefficient is about 0.2,which indicates that the upper atmosphere zone between 100 and 200 km can be utilized for flying vehicles in terms of aerodynamic force.Therefore,it is meaningful to carry out the upper atmosphere aerodynamics research for the development of upper atmosphere vehicles.