Turbulence
How does turbulence break into stripes in a channel flow?
Open access · cc by · source: Europe PMC
As a channel flow slows toward laminar, turbulence organizes into tilted stripes whose angle stays near 25 degrees before the pattern breaks up, while the friction coefficient stays roughly constant.
Study at a glance
- Design
- Computational / modelling — Direct numerical simulation of pressure-driven plane channel flow in large periodic domains, lowering the friction Reynolds number step by step from 100 to 39.
- N
- No participant N; simulations at a series of friction Reynolds numbers between 39 and 100.
- Population
- Simulated incompressible flow between two parallel plates (plane Poiseuille flow)
- Outcome
- Turbulent band angle, laminar gap size distribution, friction factor, and moments of local Reynolds numbers and cross-flow energy
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Uniform turbulence gave way to oblique stripes with competing orientations, then to isolated parallel bands at the lowest flow rates. In the stripe regime the band angle was nearly constant at about 25 degrees, rising toward 40 degrees as the pattern fragmented, and the friction factor stayed near 0.01. Laminar gap sizes had exponential rather than power-law tails at every flow rate studied, so the whole range is intermittent but not critical. The skewness and kurtosis of wall shear stress and turbulent energy grew as the flow slowed and followed the same kurtosis-versus-skewness-squared relation seen in fully developed turbulence.
Methodology
The authors simulated fluid driven by a pressure gradient between two flat plates, using very large periodic computational boxes so many turbulent structures could coexist. Starting from fully turbulent flow they reduced the driving (the friction Reynolds number) in small steps and let the flow settle at each level. They measured the tilt of turbulent bands two independent ways, the sizes of laminar gaps between bands, the friction factor, and the full statistical distributions of local Reynolds numbers and turbulent energy.
Limitations
The lowest simulated flow rate is still above the estimated critical point, so the study cannot say how the transition itself behaves or which universality class it belongs to; the authors say that would need even bigger domains and longer runs. Results come from periodic boxes, which may impose some constraints compared with a real finite channel. The analogy with first-order phase transitions is suggested, not demonstrated, and the kurtosis-skewness relation is observed without an explanation.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Turbulence has fat tails; its rare bursts are not captured by a single average or a Gaussian.
Turbulent fluctuations are intermittent: in solar-wind magnetic data the higher-order structure-function exponents bend away from the linear prediction in the inertial range, and in simulated transitional channel flow the skewness and kurtosis of wall shear stress and turbulent energy grow as the flow slows.
Evidence for the claim as stated.
Dying turbulence does not fade uniformly; it forms tilted bands separated by laminar gaps.
Near the laminar limit, turbulence in a pressure-driven channel organises into oblique stripes tilted at about 25 degrees, rising toward 40 degrees as the pattern fragments into isolated bands, while the friction factor stays near 0.01; laminar gaps have exponential rather than power-law size tails over the simulated range.
Evidence for the claim as stated.
Dying turbulence does not fade uniformly; it forms tilted bands separated by laminar gaps.
Near the laminar limit, turbulence in a pressure-driven channel organises into oblique stripes tilted at about 25 degrees, rising toward 40 degrees as the pattern fragments into isolated bands, while the friction factor stays near 0.01; laminar gaps have exponential rather than power-law size tails over the simulated range.
Scope note — Lowest simulated Reynolds number is still above the critical point, in periodic boxes.
Limits the claim's scope: a different population, assay, or outcome.
The studies probe very different regimes: marginal wall-bounded turbulence near transition, fully developed magnetised plasma turbulence, buoyancy-driven convection at Prandtl number 10.6, and idealised isotropic turbulence. Intermittency appears in more than one of them, but their scaling laws are not interchangeable.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
The studies probe very different regimes: marginal wall-bounded turbulence near transition, fully developed magnetised plasma turbulence, buoyancy-driven convection at Prandtl number 10.6, and idealised isotropic turbulence. Intermittency appears in more than one of them, but their scaling laws are not interchangeable.
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Same topic cluster — not a recommendation engine.