Latest papers in fluid mechanics

Dynamic lift enhancement mechanism of dragonfly wing model by vortex-corrugation interaction

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): Yusuke Fujita and Makoto Iima

Dragonfly wings, with their unique corrugated structure, may achieve superior aerodynamic performance in specific flight conditions, although these conditions are not yet fully understood. This led us to investigate the vortex dynamics and lift generation as a corrugated wing transitions from a stationary state to translational motion. The results reveal that suppression of secondary vortices generated on the wing significantly improves the overall performance of corrugated wings. This advances our understanding of flight dynamics and can also contribute to applications in engineering and biomimicry.


[Phys. Rev. Fluids 8, 123101] Published Thu Dec 07, 2023

Towards a constitutive relation for emulsions exhibiting a yield stress

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): H. V. M Kibbelaar, A. Deblais, G. Briand, Y. Hendrix, A. Gaillard, K. P. Velikov, M. M. Denn, and D. Bonn

Many materials encountered around us in daily life are yield stress materials, which behave solid-like for small applied stresses, but start to flow when the applied stress exceeds a threshold. The shear viscosity of these materials is relatively well understood. However, this is far from a complete and satisfactory description of the mechanical response, and most flows are more complicated. A coherent picture for general flows is still lacking.


[Phys. Rev. Fluids 8, 123301] Published Thu Dec 07, 2023

Experiments on the unsteady massive separation over an aerofoil

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): S. Mohamed Aniffa and Alakesh Ch. Mandal

Instantaneous flow fields over a NACA 0012 aerofoil at the stall and post-stall angles of attack have been measured using the time-resolved particle image velocimetry technique. The time sequence of the measured data reveals that the massive separation over the upper surface of the aerofoil is intermittent in nature. This intermittent massive separation is due to the interchange of instability, that is, from a convective to an absolute instability and from an absolute to a convective instability. A physical mechanism for this intermittent massive separation has also been proposed.


[Phys. Rev. Fluids 8, 123901] Published Thu Dec 07, 2023

Exploring regular and turbulent flow states in active nematic channel flow via Exact Coherent Structures and their invariant manifolds

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): Caleb G. Wagner, Rumayel H. Pallock, Jae Sung Park, Michael M. Norton, and Piyush Grover

Active fluids operating at negligible Reynolds numbers can exhibit spontaneous coherent motion, dynamical vortex patterns, and mesoscale turbulence. We employ tools from nonlinear dynamical systems theory to uncover the global phase space of two-dimensional active nematic channel flow. We compute several Exact Coherent Structures (ECSs), which are exact solutions of the physical dynamics with distinct and regular spatiotemporal structure; examples include unstable equilibria, periodic orbits, and traveling waves. We provide numerical evidence to show that this collection of ECSs and their invariant manifolds act as an organizing template for the complicated spatiotemporal motion of the active fluid.


[Phys. Rev. Fluids 8, 124401] Published Thu Dec 07, 2023

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