Researchers Discover Hysteretic Behavior in Turbulent Flow Dissipation
Researchers have identified a hysteretic behavior in energy dissipation within unsteady turbulent flows, confirmed through both wind tunnel experiments and direct numerical simulations. The study shows that at the same mean Reynolds number, decelerating flows dissipate energy at a higher rate than accelerating ones, producing a measurable hysteresis cycle. The findings have broad implications for modeling out-of-equilibrium fluid systems, including atmospheric turbulence and engineering applications.
A new study posted to arXiv presents experimental and computational evidence that energy dissipation in unsteady turbulent flows is not a simple function of instantaneous flow conditions, but instead depends on the flow's history — a property known as hysteresis. Wind tunnel experiments and direct numerical simulations of oscillating flows both demonstrate that, at a given mean Reynolds number, the dissipation constant is systematically larger when the flow is decelerating than when it is accelerating. This asymmetry produces a closed hysteresis cycle under periodic forcing, whose area scales with a parameter combining the Strouhal number and the relative amplitude of the oscillation. The authors explain this behavior through the unsteady term in the Kármán-Howarth equation, a classical relation governing turbulent energy transfer. The results suggest that standard turbulence models, which typically assume a quasi-steady relationship between dissipation and flow parameters, may need revision for unsteady or periodically forced conditions.
What's missing
The study's scope is limited to oscillating flows at stationary mean Reynolds number; it remains unclear how the hysteresis scaling generalizes to flows with time-varying mean Reynolds numbers or more complex forcing geometries. The range of Strouhal numbers and forcing amplitudes tested is not detailed in the abstract.
What different sources said
- arXiv physicsCenter
Dynamical hysteresis in the dissipation in turbulent flows
Related
Gut Bacteria Enzyme Found to Break Down Heat-Processed Food Compounds, Producing Novel Biogenic Amines
Researchers have discovered that an enzyme in common gut bacteria can degrade N-epsilon-carboxymethyllysine (CML), a compound formed during thermal food processing, producing previously unknown biogenic amines. The enzyme, ornithine decarboxylase SpeC from enterobacteria, acts on CML and related modified lysine derivatives through a low-level 'underground' catalytic activity. This finding suggests a previously unrecognized communication axis between thermally processed dietary compounds and gut microbial physiology, with potential implications for host health.
Full-Length Gene Sequencing Reveals Two Distinct Bacterial Communities in Black-Legged Ticks Expanding Into Canada
Researchers used Oxford Nanopore full-length 16S rRNA gene sequencing to characterize the microbiome of Ixodes scapularis black-legged ticks collected in Nova Scotia, Canada, distinguishing between tick-adapted bacteria and environmentally acquired bacteria. The study comes as I. scapularis — the primary vector of Lyme disease — is rapidly expanding northward into Canada due to climate change. The findings suggest that environmentally derived bacteria in tick microbiomes are not mere contamination, which has implications for how tick microbiome data is collected and interpreted across surveillance studies.
Study Identifies Metabolic Link Between Cell Envelope Stress and Biofilm Formation in Bacteria
Researchers have discovered that the metabolite acetyl-CoA directly inhibits enzymes that degrade the bacterial signaling molecule c-di-GMP, connecting cell envelope biosynthesis stress to biofilm formation in Pseudomonas aeruginosa. The study found that sub-inhibitory concentrations of antibiotics targeting early peptidoglycan biosynthesis — but not other antibiotic classes — elevate c-di-GMP levels by reducing phosphodiesterase activity, with acetyl-CoA competing for the enzyme active site. Because the relevant enzyme domain is broadly conserved across bacterial species, this checkpoint mechanism may be widespread and could have implications for understanding antibiotic-induced biofilm responses.