基于气动导数的类X-37B飞行器纵向稳定性分析

为了定量地研究跨大气层轨道飞行器在不同飞行条件下俯仰方向的动态特性，在Etkin气动力模型的基础上，详细研究了飞行马赫数、减缩频率、振动幅值、平均迎角等因素对此类飞行器纵向动态特性的影响规律。研究结果表明，平均迎角和飞行马赫数决定了流场的基本特性，所以对气动导数的影响很大；而减缩频率和振动幅值决定了非定常扰动的强弱，影响非定常气动力的大小，决定非定常迟滞效应的强弱。对类似X-37B的跨大气层轨道飞行器来说，平均迎角越大，机身后方背风区的涡流作用越强，纵向稳定性越强。在亚声速范围内，随着飞行马赫数增加，纵向稳定性增强，在超声速范围内，随着飞行马赫数增大，纵向稳定性减弱。振动幅值大小虽然影响了流场的形态，但对气动导数的数值大小没有明显影响。振动频率对动态特性的影响也不明显。希望研究结果可为中国未来类似飞行器的研究和发展提供相应的参考和技术储备。 

Longitudinal stability analysis for X-37B like trans-atmospheric orbital test vehicle based on aerodynamic derivatives

In order to quantitatively examine the dynamic characteristics in pitching direction of the tans-atmospheric orbiter under different flight conditions, on the basis of the Etkin aerodynamic model, the effects of Mach number, reduced frequency, oscillation amplitude, and average angle of attack on longitudinal dynamic performance of the orbiter were studied in detail. The results show that the average angle of attack and the Mach number determine the basic characteristics of the flow filed, so they have a great effect on the aerodynamic derivatives. The reduced frequency and oscillation amplitude determine the strength of the unsteady disturbance and that of the unsteady hysteresis effect, so they have a great effect on the unsteady aerodynamic forces. For X-37B like trans-atmospheric orbiter, with the increase of the average angle of attack, the effect of the vortical structure at the leeward side of the afterbody is larger and the longitudinal stability is increased. In the subsonic range, as the Mach number increases, the stability increases, and in the supersonic range, as the Mach number increases, the stability decreases. Although the amplitude has some effects on the flow field, it has no significant effect on the value of the aerodynamic derivative. The influence of oscillation frequency on dynamic characteristics is also not obvious. And we hope that these conclusions would provide some technical guidelines and reference for the future research and development of similar vehicle in China.