Linearized Stability and Gust Response Aeroelastic Analysis of a Launch Vehicle

The scope of the work is to develop a methodology for more reliable and efficient reduced-order models (ROM) for a linearized analysis of the aeroelastic stability and gust response of Launch Vehicles (LV). The approach has allowed to analyze the aeroelastic performance of an LV in the neighborhoods of actual flight conditions in supersonic regime and it has also allowed to predict the aeroelastic behavior of a developed future version of the LV under study . Aeroelastic analysis of LVs is an essential part of their design procedure. Nonetheless, as a result of the lack of validated commercial codes and experimental tests on full-scaled or scaled model, in most cases, the analysis is limited to static aeroelastic instability analysis (divergence). Indeed, the dynamic aeroelasticity for LVs is not as developed as that of the fixed wings. The direct employment of numerical CFD simulations for a fully coupled fluid-structure model is typically very expensive from a computational point of view and practically not useful in a LV design phase. Thus, there is space, in the authors’ opinion, to address this kind of aeroelastic dynamic stability analysis by a modal-based approach. In the first part of the paper, a linearized dynamic aeroelastic analysis of a LV is addressed: the approach is based on integrated dynamic aeroelastic/CFD modeling methodology. Specifically, it consists of using a global modal description for the structural dynamics of the launcher in terms of the natural frequencies and modes of vibration, coupled with an unsteady Euler-based aerodynamics in the neighborhoods of a flight condition. The generalized-aerodynamic-force (GAF) matrix is identified, via linearization process, in an high-subsonic flow phase and in presence of an angle of attack performing several prescribed modal-transient boundary conditions on a Euler-based CFD code. Thereby, a generalized (iterative) eigenanalysis is performed to study the aeroelastic stability on the linearized model of the LV in the prescribed flow condition. In the second part of the paper, a vertical gust input has been considered for the LV by including the effects on the unsteady pressure field of a rigid transversal modal transient boundary condition on the same Euler-based CFD code: the identified modal gust vector allows to determine the complete frequency gust response matrix for the LV at the prescribed flight conditions.The approach has been applied to the stability and gust response analysis of LYRA LV, enhanced-designed version of VEGA LV, the single-body multi-stages launcher recently developed by the European Space Agency (ESA). Indeed, the methodology has been considered as an actual tool for the aeroelastic analysis and design of LVs.