非定常气动力理论

Theories of Unsteady Aerodynamic Force

从经典的飞行器瞬态流到振荡流,再到千奇百怪的生物推进与飞行模式和无人飞行器、微型飞行器,非定常气动力问题涵盖十分广泛的流动范畴,涉及复杂的非定常分离流,如自由剪切层和集中涡等局部流动结构的演化与相互作用。为了根据计算或实验得到的复杂非定常流场做出理性诊断,查明每个局部结构对合力的贡献,极有必要发展在流体中任意运动与变形的物体所受的气动力(包括水动力)的一般基础理论。本文首先提出两个原则:一是局部结构对合力的贡献要满足伽利略不变性要求;二是物体的自主运动需要给出物体的质量分布与惯性矩,同时考虑合力与力矩。然后介绍几类主要的理论及其应用案例。最简洁而广泛的理论是不涉及动量方程的冲量理论,包括经典的全域理论、经典与现代的无黏理论、最小域冲量理论及其可压缩推广。第二类理论是动理学的因果型理论,包括扩散型和边界型合力公式。第三类理论是加权型理论,包括几种投影理论和虚功理论,重点是能自动满足局部伽利略不变性的加权压力源理论。随着非定常气动力诊断需求的继续发展,可以期待未来还会出现新的理论。

From aircraft transient flow and oscillatory flow in classic aerodynamics,to diverse biological propulsion and flight modes,as well as unmanned aerial vehicles and micro air vehicles,unsteady aerodynamics covers a wide range of flow categories,involving complex unsteady separated flows,such as the evolution and interaction of local flow structures such as free shear layers and concentrated vortices.In order to make a rational diagnosis based on the complex unsteady flow field obtained from computation or experiment,and to identify the contribution of each local flow structure to totalforces,it is extremely necessary to develop a general basic theory of the aerodynamic force(including hydrodynamic force)acting on arbitrary moving and deforming bodies in fluid.This paper first proposes two principles:Firstly,the contribution of local flow structures to the total force should be Galilean invariant,and secondly,for autonomous motion of a body,it is necessary to know the body's mass distribution and moment of inertia,and consider both the force and moment.The article then introduces several major theories along with specific case studies.The most concise and extensive theory is the impulse theory that does not involve the momentum equation,including classical global theory,classical and modern inviscid theory,minimum-domain impulse theory,and its compressible extension.The second type of theories is the causal theory focusing on kinetics,including diffusion-type and boundary-type force formulas.The third type is the weighted theory,such as various projection theories and vitual work theory,with focus on the weighted pressure-source theory that can automatically satisfy local Galilean invariance.With the continued development of the demand for unsteady aerodynamic diagnosis,new theories canbeexpectedtoemerge inthefuture.