Numerical Analysis On Span Dominated Ground Effect And Application Design Of Wing In Ground Effect

When wing-in-ground crafts are flying near the ground,in addition to Chord Dominated Ground Effect which means the air blocked under the wing and lower surface pressure increased,there exists Span Dominated Ground Effect,which means that the formation of the free vortex at the trailing edge of the organic wing is suppressed and downwash is weakened,causing that the lift is increased,and the induced resistance is reduced.Span Dominated Ground Effect,however,is rarely studied from the two-dimensional to three-dimensional cases.Span Dominated Ground Effect on the aerodynamic characteristics and stability of the wing in ground effect is to be studied.The similarity theory about data of numerical calculation or experiment applied to predicting results of prototype design has not been established,and there is no application-optimized design reference for the wing in ground effect.The aerodynamic characteristics of the NACA4412 rectangular wings with different aspect ratios at different flying heights and angles of attack are calculated using the SST model.The parameters of stability are obtained by the differential method.Under the same condition of relative flying height and angle of attack,the slope of the increase of the lift coefficient of the three-dimensional ground effect wing decreases as the aspect ratio increases.At the same angle of attack,the slope of the lift coefficient with respect to the relative flying height increases as the aspect ratio increases;and at the same relative flying height,the slope of the lift coefficient with respect to the angle of attack increases as the aspect ratio increases.The trend of the downwash angle of the numerical calculation is consistent with the result of the classic Wieselsberger formula.It has been found that aspect ratio,flying height and angle of attack have little influence on the aerodynamic center of pitch.The aerodynamic center of height diverges with the increase of the flying height,which is also different with aspect ratio,which makes it difficult to predict the static stability of the wing in ground effect.Based on flow similarity principle,physical quantities related to the flow system where wing-in-ground crafts are flying close to the surface of water are taken into consideration and the similarity theory of wing-in-ground craft is formed.According to the Buckingham Pi theory,in respect of thin wing in ground,the function of the lift coefficient or the pitching moment coefficient about flying height and angle of attack are established.Similarly,the functional of the drag coefficient about Reynolds number,relative flying height and angle of attack is also established.Then the application of date that comes from numerical calculation or experiment to the results of prototype design can be realized.The genetic algorithm is used to optimize the design of the combination of wing in ground effect and horizontal tail.Force analysis is used to analyze the relationship between static stability and design variables.The calculation of objective function value takes advantage of the former results of numerical calculation by interpolation,and the single objective optimization is used to validate multi-objective optimization.The Pareto optimal set obtained by the multi-objective genetic algorithm provides choices for different requirement of weights of target in practical engineering problem.