The Unsteady Aerodynamic Characteristics Of A Wing Above Sea-Waves

The wing-in-ground-effect (WIG) vehicle is a new type of high performance vehicle with many advantages such as high speed, good economics, good stealth, easy to take off or land, and so on. It has great value to be used in martial and demotic fields. Either to be a platform for originating an attack to the enemy or to be a vehicle for landing force, the WIG vehicle must fly with low altitude in martial action. It is also a valuable topic that how to take advantage of the good interaction and avoid the potential dangers as flying at lower altitude in demotic application. It is necessary to study the unsteady nonlinear aerodynamic characteristics of a WIG flying in air with disturbed waves for the design of high-performance WIG vehicle, especially for the subject that how to improve the safety, maneuver ability near sea wave, and economics of the WIG flying over sea waves.Based on the potential theory, linear and fully nonlinear aerodynamic forces and motions of a wing flying above sea-waves are studied numerically. And the effects of the characteristic parameters of wing and sea waves on the aerodynamic forces are acting on the WIG are analyzed systematically in this thesis. Some meanful problems are discussed, and useful results have been obtained.Firstly, a representative wind and wave model, which could both simulate the main characteristics of WIG over sea waves and be suitable for numerical calculation, is presented. The model completely considers the fully nonlinear effect of wave surface on the wavy air flow, separates the disturbance of wave surface from the wing-air wave interaction flow, and overcomes the numerical calculation difficulties due to the large difference of dimensions between wing and water waves.An improved numerical method is presented through in-depth numerical analysis of the factors affecting the accuracy of numerical calculation. By reasonably matching the numerical grids to the mathematic model used, the present method can make the numerical calculation processed with high accuracy. Additionally, a local mapping method is presented for simulating the wave interaction. This method makes it possible for investigating the unsteady nonlinear potential flow in a complicated environment with higher efficiency.The aerodynamic forces of a wing in couple motion of heave and pitch withground effect are analyzed in detail based on the numerical result. It is shown that a thrust force exists when the wing is in heave motion. The thrust, which is proportional to the amplitude of heave speed, decreases as the frequency of motion increases. The pitch motion can adjust the force and efficiency of thrust, which is induced by heave motion. The effect is decided by the phase of two motions. The ground effect increases the thrust force and efficiency.A new viewpoint to the albatross's high performance of flight near wave surface is presented in this paper. How the albatross can realize it high performance flight above waves by taking advantage of wavy effect and boundary effect is illustrated in details.Three models are employed to analyze the aerodynamic characteristics of a wing above sea-wave. Those are (1) curve surface effect (C.E.), (2) wavy air motion effect (W.E.) and the coupled effect A.E. of C.E. and W.E.. Numerical results are as following.1. C.E. depends on the wave amplitude, altitude and the chord of wing. The C.E. decreases rapidly when the altitude increases. The C.E. is nonlinear significantly when the sea amplitude is considerably large. The C.E. in both 2D and 3D problem increase the lifting forces, the C.E. in 3D problem decreases the' drag coefficients, but the C.E. in 2D increases the drag a little.2. W.E. attenuates slower than the C.E., when the wing fly high enough, the C.E. is the main effect to the aerodynamic characteristics.3. The larger the chord, the stronger the C.E. and W.E. are.4. The coupled effect is very strong when the wing fly close to the sea surface.