Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.14316

Finding a reconnection in a vortex-haystack

Abhishek Harikrishnan·Benjamin Musci·Adrien Lopez·Bartosz Protas·Adam Cheminet·Jean Le Bris·Jean-Marc Foucaut·Jean-Philippe Laval·Christophe Cuvier·Pierre Bragança·Bérengère Dubrulle
View original source ↗Read source document ↗Export metadata ↓

Abstract

Counter-rotating vortex reconnection is a topology-transforming event that leads to strong vorticity amplification and is often associated with the most irregular regions of the velocity field. Detecting such events directly in turbulent flows is a major challenge due to the ambiguity inherent in the definition of a vortex and the rapid proliferation of intense small scale vortices. We develop a novel methodology by combining two tools. The first is a local in scale, space and time regularity indicator that isolates spatio-temporal regions of interest. The second is a reconnection indicator that exploits a well-known property of vortex reconnection namely, that the enstrophy (volume integral of the square of vorticity) flows from the symmetry to the collision plane. To examine the flow of enstrophy in the correct reference frame, a new method inspired by orientational order parameters in liquid crystals is developed. We then show a proof of concept for our reconnection indicator by comparing it with diagnostic methods available in the literature. The method is validated on experimental datasets from a turbulent von Kármán flow at two different resolutions, one of which allows us to probe the flow below the Kolmogorov scale, $η$. Our findings suggest that counter-rotating vortex reconnection could be a potential mechanism for the creation of motions at scales below $η$.

Explore related subjects

physics.flu-dyn

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Abhishek Harikrishnan, Benjamin Musci, Adrien Lopez, Bartosz Protas, Adam Cheminet, Jean Le Bris, Jean-Marc Foucaut, Jean-Philippe Laval, Christophe Cuvier, Pierre Bragança, Bérengère Dubrulle. 2026-10-09. Finding a reconnection in a vortex-haystack. https://arxiv.org/abs/2610.14316

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Lacunarity in a Two-Dimensional Atomizing Liquid Jet

Atomization stretches and folds the liquid--gas interface before fragmenting it into ligaments and droplets, making fractal measures a natural descriptor of the lacunarity of the final breakup state. We examine this idea in two-dimensional (2D) VOF-DNS of a liquid jet with adaptive mesh refinement in Basilisk. Box-counting of the full resolved interface does not yield a single scale-independent exponent. Instead, two scaling ranges appear, separated by a crossover near the box-counting level \(L_{\mathrm{box}}\simeq7\): coarser boxes measure the folded connected jet envelope, whereas finer boxes increasingly sample ligaments, droplets, and nearly smooth local interface segments. Decomposing the interface into detached droplets, ligaments, and the connected main body shows that the relevant effective dimension is structure dependent. Droplets are most lacunar with dimension below one, ligaments occupy an intermediate level, and the main body carries the largest coarse-scale dimension. This hierarchy persists over $Re_l=100$--$10^4$ at fixed $\We_g=200$. The lacunarity of droplets is reminiscent of that of the object positions in the night sky hypothesized by de Vaucouleurs.

physics.flu-dyn↗
arXiv2026

Generalizable turbulence closures across bluff-body shapes by PINN-based solver-agnostic training

Data-driven turbulence closures are commonly calibrated by embedding a CFD solver within an inverse procedure that requires a converged flow solution at every optimization iteration, which is fragile and costly. We instead formulate closure identification as a PDE-constrained, data-driven inverse problem within a physics-informed neural network (PINN), and subsequently stabilize the inferred closure for deployment in a numerical solver. This separation eliminates the training cost of repeated CFD solves and associated adjoint or ensemble evaluations, providing substantial flexibility to investigate alternative closure forms. Using this flexibility, we develop four closures: three model the Reynolds stress on a realizable tensor basis---a local map, a non-local model transporting the turbulent kinetic energy and recovering the out-of-plane normal stress, and the same with a learned length scale $\ell$---and a fourth models the Reynolds force $\mathbf{F}=-\nabla\cdot\boldsymbolτ$ directly, free of the realizability constraint. All four are trained across six two-dimensional bluff-body wakes at $Re=10^4$ and deployed frozen in a standard finite-element solver, stabilized primarily by input-gradient smoothing. Under a strict leave-one-shape-out (LOSO) protocol, all four reduce the field errors of a steady SST $k$-$ω$ baseline, most strongly on the mean velocity. The learned-length-scale closure is most accurate on the stress fields, while the force model generalizes best on the mean velocity and drag (LOSO drag error $\sim 7\%$). The closures also train efficiently on Particle Image Velocimetry data, enabling geometries intractable for DNS.

physics.flu-dyn↗
arXiv2026

Effect of leading edge geometry on aerodynamic performance of a flat plate

Flow separation around flat plate is influenced by the thickness and leading edge geometry, which creates the shear stresses and pressure distribution manifesting into unsteady aerodynamic forces. Leading edge geometries have been widely reported but the influence of leading edge curvature at low Reynolds numbers (Re) have found less attention. The present study uses two dimensional numerical simulation to investigate the effect of a hemispherical curvature (protuberance) at the leading edge and reports how vortex shedding, shedding frequencies and aerodynamic forces are affected over a range of angles of attack ($0^\circ \leq α\leq 25^\circ$) at Re = 1000. Thicker vortical regions are formed near the plate with curvature at the leading edge. Onset of shedding is noted at angle of attack of $5^\circ$ for the plate with curvature at the leading edge and it gets delayed for simple flat plate. The temporal force coefficients on the plates show multiple frequencies at higher angles of attack. The plate with curvature at the leading edge has a glide ratio of 1 at $0^\circ$ angle of attack and has equivalent glide ratio to that of simple flat plate at higher angles of attack. The simple flat plate has better glide ratios at moderate angles of attack like $5^\circ, 10^\circ$ and $15^\circ$. The results will help in making engineering informed design decisions for smaller unmanned aerial/aquatic vehicles cruising at low Reynolds numbers.

physics.flu-dyn↗