Sensitivity analysis for the aeroelastic stability of a launch vehicle

In this paper, a linearized aeroelastic analysis of a launch vehicle (LV) during its critical flight conditions together with a sensitivity study are presented. Specifically, a modal description for the structural dynamics of the launcher in terms of the first natural frequencies and modes of vibration and an unsteady aerodynamic model obtained performing several prescribed modal transient boundary conditions on a laminar-based CFD code has been carried out. The modal input/output analysis for the aerodynamics, performed in the frequency domain, allows to identify the linearized unsteady aerodynamic operator 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 Lagrangean 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. 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 order to check the local stability of the LV. Finally, an estimate of the uncertainty of the obtained stability aeroelastic margins obtained with the above procedure has been performed and investigated in terms of angle of attack, Mach number, flight speed and air density.