飞行器低Reynolds数层流分离理论探讨

低Reynolds数流动由于自身特点导致气动特性严重恶化，非定常、非线性效应突出且预测困难，加之相关基础理论研究不足，给以临近空间低速飞行器和高性能微小型飞行器为代表的低Reynolds数飞行器的开发和研制带来了瓶颈和挑战.首先概述了飞行器低Reynolds数的范畴、低Reynolds数空气动力学的主要问题与挑战.随后从低Reynolds数层流分离基础理论出发，依次介绍了低Reynolds数层流分离经典理论、低Reynolds数层流分离非定常流动特性、低Reynolds数后缘层流分离泡.在此基础上，通过对经典长层流分离泡与后缘层流分离泡力学特性的差异以及随攻角和Reynolds数的演化规律的详细分析，逐步揭示了一些低Reynolds数复杂气动效应的本质，如小攻角升力系数的非线性效应，翼型随Reynolds数下降气动特性的二次恶化效应等.最后对低Reynolds数流动基础理论的发展过程进行了总结，并对层流分离诱导转捩及再附效应等复杂流动问题进行了展望. 

Discussion about the Laminar Separation Theory at Low Reynolds Numbers

The aerodynamics sharp decrease, unsteady and nonlinear effects and low prediction accuracy at low Reynolds number result in lots of difficulties and challenges in developing low Reynolds number aircraft, such as near space low speed aerial vehicle and micro aerial vehicle. This paper firstly summarized the region with low Reynolds number and the main problems and challenges of low Reynolds number aerodynamics. Secondly, at low Reynolds number theory aspects, this paper respectively introduced the classical low Reynolds number laminar separation theory, the unsteady flow aerodynamics characteristics at low Reynolds number and trailing-edge laminar separation bubbles. On this basis, with detailed analysis about the aerodynamic differences between classical long laminar separation bubble and trailing-edge laminar separation bubble and the revolution regulation with the changes of the attack of angles and Reynolds numbers, the essence of complicated aerodynamic effects at low Reynolds number has been revealed, for instance, lift nonlinear effect at low attack of angles, secondary deterioration effect of airfoils with decreasing Reynolds numbers. This paper lastly concluded the deve-lopment process of low Reynolds number basic theory, and made outlooks to complicated issues such as transmissions induced by laminar separation and attachment effects after separation.