ReCoVor

Abstract: Fluid-structure interactions between elastically mounted pitching plates and uniform flow produce a diverse set of aeroelastic responses, including static and dynamic instabilities, limit-cycle oscillations, and chaotic dynamics. In these systems, large-amplitude oscillations often occur at low flow speeds and coexist with vortex-dominated wake dynamics.

This talk presents cyber-physical investigations of an inverted flag aeroelastic system consisting of a rigid plate mounted on a trailing-edge torsional spring and aligned parallel to a uniform freestream flow. Aerodynamic loads are imposed physically in a subsonic wind tunnel (Re ~10^5), while structural loads are imposed artificially using an electromechanical control loop. This framework allows for exploration of complex nonlinear structures with variable damping levels, ultimately leading to the design and optimization of a fluid-oscillator energy-harvesting platform.

Results are presented through bifurcation diagrams, reconstructed phase-plane portraits, and flow visualizations. Both linear and nonlinear spring designs are examined. Linear spring experiments detail distinct straight, flapping, and deflected flow regimes and serve as a baseline case for validating the cyber-physical framework. Hardening spring designs extend dimensional excitation regimes, providing guidance for future energy-harvesting efforts. Lastly, cubic spring designs facilitate a targeted investigation into underlying excitation mechanisms by removing the straight flow regime observed in the baseline experiments. 

Abstract: How can you ensure a balance between accuracy and performance when doing adaptive direct-numerical-simulations of complex moving geometries? While classical adaptive codes usually focus on heuristic measures as an error indicator, this presentation explains the benefit of using the wavelet decomposition for multi-resolution analysis as well as error control and how we use it to resolve the turbulent structures shed by flapping insect flight. Our solver WABBIT solves the incompressible Navier-Stokes equations by continuously ensuring a sufficient representation of all necessary scales at each time-step, the domain is discretized on a block-based octree grid and the solution evolved with a higher order projection method. The ansatz and its robustness will be validated for a challenging inviscid, incompressible test-case of crashing vortex tubes forming a near-singularity, portraying how the adaptation can be adjusted to accuracy requirements. The results on the finest grid with an effective resolution of 8192^3 match well with the pseudo-spectral one from Hou&Li, while maintaining a grid compression lower than 0.2%. Together with the volume penalization method, the adaptive framework allows for a flexible approach to easily deploy efficient simulations for different insects and flight scenarios.