定常升阻力普适理论的特色和升力的物理来源

现代空气动力学诞生一百多年来, 已经发展出众多关于升力和阻力的理论. 但是, 其远场合力理论一直停留在低速不可压流. 虽经几代人的努力, 但仍未能把它精确地推广到黏性可压缩流. 这种状况直到最近才得以突破. 本文作者及其合作者依据对远场线化Navier-Stokes方程解析解的研究, 获得了经典不可压二维定常流的Kutta-Joukowski升力定理的现代二、三维普适版这个核心结果, 从而突破了经典空气动力学基础理论延续了八九十年的一个缺口. 基于线性近似得到的简洁公式, 何以能在高度非线性的复杂流场中仍然精确成立, 这里涉及饶有兴趣的方法论问题, 很值得关注. 本文的第一个任务, 是在简要回顾普适理论基本成果的基础上, 反思其方法论特色和背后的物理机理. 尽管严格的量化升力理论已经得到航空实践的广泛检验, 但在各种出版物和媒体上仍常常出现关于升力物理来源的各种假说. 这种状况表明: 升力物理来源这个问题, 并没有在国内外众多的教科书、专著和课堂中得到彻底的澄清, 认真回答这个问题在现今仍然具有迫切的重要性. 普适理论的普遍有效性和高度简洁性使人们能用它以尽可能直接的方式为澄清升力来源提供逻辑严密的论据, 值得着重考察. 这是本文的第二个任务. 

The universal steady lift and drag theory and the physical origin of lift

Since the birth of modern aerodynamics, various theories on lift and drag have been developed and validated extensively in aeronautical applications. However, the far-field force theory had long remained at low-speed incompressible flow. Based on the analytical solutions of the linearized Navier-Stokes equations in the steady far field, the authors and their collaborators extended the classic Kutta-Joukowski lift theorem to both two- and three-dimensional viscous and compressible flows, and thus filled the long-standing gap in theoretical aerodynamics. Why can the simple formulas based on linearized approximation still be accurately valid for highly nonlinear complex flows? This issue of great interest involves the methodological characteristics and physical mechanism behind the unified force theory and is the first task of this article. Moreover, there has been an abnormal phenomenon regarding the physical origin of lift that, despite the already mature and fully verified rigorous lift theory, various different hypotheses still keep surfacing frequently in various nonscientific publications and media. This indicates that the issue is really complicated and has not been thoroughly clarified in textbooks, monographs, and classrooms around the world. Now, the universality and high conciseness of the unified theory enable one to reach a clear answer to this issue by rigorous logical arguments in the most direct way. This is the second task of this article.