Periodic Reporting for period 4 - AEROFLEX (AEROelastic instabilities and control of FLEXible Structures)
Reporting period: 2020-01-01 to 2020-06-30
As a result of those primary flow-induced instability, periodic oscillations of structures may arise, as for the aeroelastic flutter limit cycle oscillations. They may alos be induced by an external forcing, as in the case of flapping bodies. In obth cases, theoretical and numerical methods are dveloped to analyze the stability of those periodic solutions. The growth or decay of perturbations is analyzed based on Floquet theory, by accounting for the coupling between the fluid and solid perturbations. An unconventional Time-Spectral-based method is developed for computing the leading Floquet modes. This time-spectral method is also used to determine unstable periodic solutions that cannot be computed with classical unsteady simulations. The challenging task of solving the Time Spectral equations is tackled via a time-parallel Newton-Krylov approach and an efficient parallel block-circulant preconditioner developed during the project. Finally, the control of flow-induced instabilities is investigated in the framework of adjoint-based optimization where the objective function is either the eigenvalue (growth/frequency) of fluid-solid eigenmodes or the energetic gain of resolvent modes. We focused on solid actuations and consider the control of fluid-solid eigenmodes of a flexible splitter plate by (i) optimizing the shape of the rigid cylinder to which it is attached or (ii) by modifying the material properties of the splitter plate with shunted piezo-electric patches. Then we address the attenuation of Tollmien-Schlichting developing in a boundary layer flow by (iii) optimizing the material properties of the visco-elastic patch inserted in the wall or (iv) actuating the vibration modes to optimally minimize the flow perturbation that are maximized by the inflow excitation.
https://w3.onera.fr/erc-aeroflex/journal-papers. They concern:
- Linear stability analysis of hyperelastic structure strongly coupled to an incompressible flows with the Arbitrary-Lagrangian–Eulerian method
- Global stability analysis and control of flexible splitter plates interacting with a circular cylinder’s wake flow.
- Resolvent analysis and optimization of visco-elastic patchs for the attenuation of boundary-layer flow instabilities.
- The global stability analysis of a springs-mounted plate revealing the viscous effect on the flutter restabilization
- The role of flow nonlinearities on the nature of the flutter bifurcation (hard versus soft flutter) depending on the mass ratio and Reynolds number.
- The self-propulsion of flapping foils at low and large flapping frequency: