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 total forces,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 virtual 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 can be expected to emerge in the future.
unsteady flowbiofluid mechanicslocal Galilean invarianceautonomous motionglobal impulse theoryminimum-domain impulse theorycausal theory of total forceprojection theoryweighted pressure-source theory
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维普
