Sensitivity analysis for the aeroelastic stability of a launch vehicle

Paper number

IAC-06-C2.7.11

Author

Dr. Franco Mastroddi, University of Rome "La Sapienza", Italy

Coauthor

Dr. Fulvio Stella, University of Rome "La Sapienza", Italy

Coauthor

Dr. Gian Mario Polli, University of Rome "La Sapienza", Italy

Coauthor

Dr. Fabio Paglia, University of Rome "La Sapienza", Italy

Year

2006

Abstract

The stability prediction of the aeroelastic behavior of a launch vehicle (LV) during its critical flight conditions has been previously performed by developing a linearized aeroelastic modelling. Specifically, such a model has been based on a linearization of the aeroelastic free response of the system in the neighborhood of a specific flight phase in presence of an angle of attack. Indeed, the static and dynamic aeroelastic stability for launch vehicles is a research field not as developed as that of the fixed wings which have deeply characterized the history of the aviation and has a research development of about one hundred years. The lack of validated commercial codes and experimental tests on full-scaled or scaled model is a motivation for addressing this kind of analysis towards a direct employment of a numerical simulation. This is typically  very expensive from a computational point of view and practically not useful in a LV design phase. Thus, in the present paper, a linearized aeroelastic analysis of a LV has been utilized. This consists of using a modal description for the structural dynamics of the launcher in terms of the first natural frequencies and modes of vibration. Furthermore, a linearized unsteady aerodynamic model obtained performing several prescribed modal transient boundary conditions on a Euler-based CFD code was been carried out. The achieved mode shapes are employed to impose elementary unsteady boundary conditions for the aerodynamics and, on the other hand, to project of the consequent aerodynamic loads. The modal input/output analysis for the aerodynamics, performed in  the frequency domain, allows to identify the unsteady aerodynamic operator linearized in the neighborhood  of the specific flight condition. 

Both the structural and aerodynamic models are finally employed in the aeroelastic coupled model given by the generalized Lagrange equations of motion. These linearized equations (time dependent ordinary differential equations, ODE), describing the aeroelastic behavior of the launcher, have, as unique unknowns of the problem, the modal coordinates chosen to describe the linearized motion. Finally, in order to check the local stability of the LV, an eigenanalysis 
(in terms of aeroelastic system poles or eigenvalues) on the linear ODE model recast in a first order form, has been performed. In the present paper an estimate of the uncertainty of the obtained stability aeroelastic margins obtained with the above procedure will be performed and investigated on the basis of estimated errors and uncertainties of the proposed aeroelastic 
modeling procedure.

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