Study On The Unsteady Aerodynamics Characteristics For The Morphing Airfoil

Morphing aircraft is a bran-new concept proposed to meet the needs of the rapid development of aerospace technology, which is able to adapt to multi-environment and perform multi-mission. Compared with the traditional aircraft with fixed-shape, morphing aircraft can self-adaptive morph according to flight circumstance and battle mission to maintain an all-stage optimal performance throughout the flight and mission. The morphing flight technology is widely regarded as one of the potentially revolutionary technology to realize the new breakthrough of the future aviation aircraft.The advantage of morphing aircraft makes it become a research hotspot in recent years. Aerodynamic characteristic is the fundamental for the research of morphing aircraft. As a bran-new research field, its scientific fundamentals and key technology for morphing aircraft are still in beginning stage. In this thesis, how to change the airfoil shape to adapt the different flight conditions is studied.The studies are carried out based on the morphing Joukowski airfoil, using the theoretical analysis and numerical simulations to study the unsteady aerodynamic characteristics for2D-morphing airfoils. The works can be summarized as follows:1. As an initial study on the theoretically investigating the unsteady aerodynamic characteristics for morphing airfoil, under the inviscid incompressible ideal fluid flow conditions, we derive the unsteady aerodynamic lift and resistance formula for the morphing Joukowski airfoil by using complex function theory. These analytical results can be used to test the program code for numerical simulations of morphing airfoil.2. Under the inviscid incompressible ideal fluid flow conditions, the unsteady flow field and aerodynamic lift for the morphing Joukowski airfoil are calculated by combining the analytical solution and the discrete vortex method together. The error sources of the quasi-steady assumption are analyzed rigorously and correspondingly the error correction method is proposed. Numerical calculations show that the vortex wake of morphing airfoil has almost no effect on the lift coefficient and the circulation around the airfoil. The additional unsteady aerodynamic lift caused by unsteady fluid flow due to the airfoil deformation is the main error source of the quasi-steady solution for the aerodynamic lift of morphing airfoil. It is also shown that the temporal flight attitude, the airfoil profiles and the deformation velocity determine the unsteady additional lift coefficient, which has little relation with the evolutionary history of deformation. It is proposed that the lift coefficient of morphing airfoil is approximately equal to the lift coefficient of the quasi-steady assumption solution adding the corresponding additional unsteady lift coefficient.3. The subsonic flow for the morphing Joukowski airfoil is transformed into incompressible flow by using an affine transformation. Then the subsonic flow can be calculated with the inverse affine transformation from the corresponding incompressible flow problem, which is solved by combining the analytical solution and the discrete vortex method together. In this chapter, for the quasi-steady aerodynamic force and the additional unsteady aerodynamic lift caused by the virtual mass force, the simple relationships between the subsonic flow and the corresponding incompressible flow are proposed. The aerodynamic characteristics of the morphing airfoil during reciprocating deformation are investigated.4. The two-dimensional small-perturbation equations governing the supersonic flow-past the morphing airfoils are calculated using the boundary element method based upon the Green formula. The unsteady supersonic aerodynamic characteristics for morphing airfoil are studied analytically and numerically. The relationships for the unsteady lift coefficient as a function of the geometry parameters for the morphing airfoil are discussed. The influences of different free-stream Mach, the angle of attack and morphing acceleration on aerodynamic characteristics during the reciprocating deformation are obtained.In summary, the study for unsteady aerodynamic characteristics of two-dimensional morphing Joukowski airfoil by theoretical analysis and numerical calculation is performed under the incompressible, subsonic and supersonic flow conditions for inviscid fluid. The research of this work is expected to have a practical help to the engineering practice in the future.