BWhat changed
Chantry, Tuckerman and Barkley simulated large domains of stress-free, sinusoidally forced Waleffe shear flow using four wall-normal modes. Near a fitted transition they found a growing turbulent fraction and gap statistics broadly consistent with directed-percolation scaling. A smaller simulated domain instead displayed long-lived transients and an apparent jump, illustrating how finite size can change the observed transition.
Scientific scope
Chantry, Tuckerman and Barkley simulated large domains of stress-free, sinusoidally forced Waleffe shear flow using four wall-normal modes. Near a fitted transition they found a growing turbulent fraction and gap statistics broadly consistent with directed-percolation scaling. A smaller simulated domain instead displayed long-lived transients and an apparent jump, illustrating how finite size can change the observed transition. This is numerical evidence for a particular truncated, drag-modified flow, not a proof of universal behavior of all wall-bounded or channel flows. The streamwise gap distribution near the chosen threshold did not exhibit the expected extended power law; the authors used an alternative correlation-length comparison and suggested finite distance from criticality. Some data collapses use directed-percolation exponents, and exponent relations make several comparisons non-independent. Threshold and exponent come from selected fits, not exact infinite-time results. The supplementary movie, raw simulations and independent fit replay were not examined.
Evidence
The linked original works support the scoped statement and contribution attribution. WRS has not independently replayed experiments or reconstructed a full mathematical proof. This is numerical evidence for a particular truncated, drag-modified flow, not a proof of universal behavior of all wall-bounded or channel flows. The streamwise gap distribution near the chosen threshold did not exhibit the expected extended power law; the authors used an alternative correlation-length comparison and suggested finite distance from criticality. Some data collapses use directed-percolation exponents, and exponent relations make several comparisons non-independent. Threshold and exponent come from selected fits, not exact infinite-time results. The supplementary movie, raw simulations and independent fit replay were not examined.
Contributors
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