On The Calculation Methods Of Aerodynamic Force And Moment In Airship Modeling

In recent years,airship control technocountries and scientific research institutions.Modeling is the basis of airship logy has become a research hotspot in many technology research,and the calculation and analysis of airship aerodynamic characteristics is the basis of airship modeling.Therefore,it has great theoretical and practical significance to study the aerodynamic characteristics of airships for airship modeling.At present,there are two main theories to study the aerodynamic characteristics of airships:inviscid flow theory summarized and perfected by Lamb et al.and vortex dynamics theory developed by J.C.Wu et al.for viscous flow field.However,Lamb's inviscid flow theory has not been widely applied to any shape of moving body for a long time,and it has been found that the moment expression in vortex dynamics theory can not converge to Lamb's result when the viscous flow field tends to zero.This shows that both inviscid flow theory and viscous flow theory need to be further developed in order to better analyze and study the aerodynamic characteristics of airships.In order to solve the above two problems,this paper studies a theory which can be applied to viscous flow field and inviscid flow field at the same time by applying the momentum theorem and momentum moment theorem only in the flow field,and derives a new aerodynamic and moment expression.This unified theory is conducive to establishing the relationship between viscous flow and inviscid flow.On the one hand,it provides a visual angle to understand Lamb inviscid flow theory from the perspective of viscous flow,and deepens people's understanding of Lamb's inviscid flow theory;on the other hand,it provides a bridge to verify J.C.Wu's vorticity moment theorem with Lamb theory,which provides a way to analyze and improve J.C.Wu's vorticity moment theorem.On this basis,the new theory is used to analyze and calculate the aerodynamic forces and moments of airships in inviscid flow.A more perfect algorithm than inviscid flow theory is obtained and the axial add mass of ellipsoid in viscous flow is calculated.The contents of this paper are as follows:(1)A new theory which can unify inviscid flow theory and viscous flow theory is studied.The expressions of aerodynamics and moments that can be applied to both inviscid and viscous flow fields are derived.The differences between the new theory and the classical theory are analyzed and discussed.The influence of the position and velocity of moment reference point on aerodynamic moments is also discussed.(2)Based on the theory deduced in this paper,the aerodynamic characteristics of the ellipsoid in the inviscid flow field are obtained.Compared with Lamb's inviscid flow results,the correctness of the new theory in the inviscid flow field is verified.The new theory is applied to calculate the aerodynamic forces and moments of general shape moving bodies in inviscid flow field.The influence of the position and velocity of the moment reference point on the moment of the moving body is analyzed by numerical examples.(3)The unsteady aerodynamic coefficients of moving bodies in viscous flow are studied.Firstly,based on J.C.Wu's vorticity moment theorem,the principle of relative motion under time-varying inflow is analyzed.Combined with computational fluid dynamics(CFD)technique and Fourier analysis method,the add mass of the hull in viscous flow is calculated when the hull is only moving axial with acceleration.Finally,the factors affecting the axial add mass of viscous flow hull are analyzed and compared with the corresponding results in inviscid flow.