Étude méthodologique des risques aéroélastiques des joints interflap

Abstract

This thesis aims to initiate the investigation of aeroelastic risks of interflap seals. The latters are located between the inboard and outboard flaps in order to ensure an aerodynamic profile. They are made of an elastomeric material and reinforced by several plies of Glass-Carbon Fiber Reinforced Plastics (G-CFRP). During test flights performed by the aircraft manufacturer, aeroelastic phenomena occurred on these parts. The issue was solved by increasing the number of plies of the reinforcement material. However, this solution is purely empirical and it makes their design quite cumbersome. A methodological study on the fluid and structure dynamics is therefore carried out in order to gain expertise to master aeroelastic risk of elastomeric structures. It should be stressed that an actual aeroelastic study is not conducted in this work. Indeed, the present work does not take into account the fluid-structure interaction which characterises aeroelastic phenomena. As a starting point, the fluid and structure dynamics are decoupled. A two-dimensional CFD analysis at low-subsonic conditions is performed and aims to identify the flow features which can be at the origin of the vibrations the seals suffered from. Additionally, it gives a more thorough understanding of the flow physics around a high-lift configuration (three-element airfoil). The analysis reveals the shedding of vortices at the trailing edge of the flap, causing quasi-periodic load oscillations on the latter geometry. The tendencies on the flow quantities of interest when the altitude and the angle of attack are modified are also identified, showing that the angle of attack may have a non-negligible impact. On the other hand, a structural analysis is done in order to extract the modal properties of the seals in their flight configuration (prestressed state). In parallel, an experimental analysis was performed in the purpose to validate the numerical model. The structural analysis allows to understand the influence of the prestress of the seals and the flap setting on the modal properties. However, those properties were obtained after the linearization of the highly non-linear structure and they must be interpreted with precaution. Finally, a qualitative comparison between the results from the CFD and structural analyses is made to briefly introduce and discuss the potential aeroelastic risks the structure may encounter in the investigated conditions. The evolution of the aerodynamic forces on the flap reports non-negligible amplitudes of oscillation with respect to the time-averaged value, especially if we consider flexible bodies such as the investigated seals. The excitation frequency at the nominal conditions is found dangerously close to the resonance frequencies of two modes of a particular stacking version of the seals. The excitation mechanism finally confirms the possibility for those modes to be excited.