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美国第一代航天飞机(Shuttle-I)在177千米高度以上飞行时处于自由分子流区(克努曾数 Kn≥10),在83～177千米的高度范围内处于过渡流区(0.001≤Kn≤10)。传统的连续介质空气动力学已不适用了,而要用非连续的稀簿空气动力学。本文简要介绍美国航天飞机研制过程中采用过的蒙特卡罗直接模拟法、粘性激波层法和洛克希德工程计算等理论计算方法。并与风洞试验和飞行试验结果进行了比较和分析。研究结果表明:低密度效应对航天飞机的气动加热、阻力系数和升阻比等气动性能有很大的影响;理论计算与飞行试验的差别随 K_n 数的增大而增大,其差別的原因尚没有确切和满意的解答。对过渡流,目前无论是理论计算还是风洞实验都存在着较大困难。因此必须加强对航天飞机低密度效应的理论和实验研究。
The Shuttle-I of the United States was in free molecular fluid zone (Knnzen number Kn ≥10) at altitudes above 177 kilometers and was in the transitional zone (0.001) at a height of 83 to 177 kilometers ≤Kn≤10). Conventional continuum aerodynamics are not applicable, but use non-continuous thin-walled aerodynamics. This article briefly introduces the Monte Carlo direct simulation method used in the development of the U.S. space shuttle, viscous shock layer method, and Lockheed engineering calculations. The results of wind tunnel test and flight test are compared and analyzed. The results show that the low-density effect has great influence on the aerodynamic performance such as aerodynamic heating, drag coefficient and lift-drag ratio of space shuttle. The difference between theoretical calculation and flight test increases with the increase of K_n number, There is no exact and satisfactory answer. For the transitional flow, at present there is a big difficulty in both theoretical calculation and wind tunnel experiment. Therefore, it is necessary to strengthen theoretical and experimental research on the low density effect of space shuttle.