How does flutter impose a limit on drag reduction by reconfiguration

Trees and plants bend and deform under the wind, we say that they reconfigure. This elastic reconfiguration enables a drag reduction. However, a flag fluttering in the wind is a good example that flexibility can lead to flow-induced vibrations with its accompanying dynamic loads.
In her new paper, Maryam Boukor investigates the ideal flexibility that enables the best compromise between drag reduction and flutter instability. The work is the fruit of collaborative work with Augustin Choimet and my colleague Éric Laurendeau
Watch the 2min summary video below and read the full paper in Physics of Fluids.

Vibration of a high-head Francis turbine runner

The runner of a high-head Francis hydraulic turbine is flattened and has vibration modes resembling those of a disc. When the runner rotates in water, the vibrating waves propagating in the direction of rotation and against rotation interact differently with water. There is therefore a doubling of natural frequencies. This implies that the turbine designer must work harder to identify these frequencies and ensure that no resonance phenomenon will occur on the turbine in operation.
This task is now (slightly) simplified by the new analytical model developed by Max Louyot as part of his master’s degree in partnership with Andritz Hydro Canada, published in the Journal of Fluids and Structures.

Review paper on FSI in plants

My review paper on the “Mechanics of a plant in fluid flow” is out in the Journal of Experimental Botany. This review covers the statics and dynamics of plant–fluid interactions, e.g., the static reconfiguration of a plant deforming under fluid flow, and also its dynamic swaying and flapping. It covers the mechanics at play in terrestrial plants as well as aquatic plants and seaweeds. Biological implications are highlighted and ideas for future research avenues are suggested.

Preprint is available here on researchgate and arXiv.