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Intermittency and coherent structures in the two-dimensional inverse energy cascade: comparing numerical and
1Laboratoire de Météorologie Dynamique, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France.
Summary
In two-dimensional turbulence, velocity distributions are Gaussian in the inverse cascade but non-Gaussian in the condensation regime. This suggests intermittency is absent in condensation, likely due to large-scale vortices.
Area of Science:
- Fluid Dynamics
- Statistical Physics
- Turbulence Theory
Background:
- Two-dimensional turbulence exhibits complex energy transfer dynamics.
- Understanding intermittency is crucial for characterizing turbulent flows.
- Coherent structures, like vortices, significantly influence turbulent behavior.
Purpose of the Study:
- To investigate internal intermittency in two-dimensional turbulence.
- To analyze velocity increment distributions across different regimes.
- To explore the role of coherent structures in intermittency.
Main Methods:
- Employed both physical and numerical experimental approaches.
- Analyzed probability distribution functions (PDFs) of velocity increments.
- Examined vorticity fields to identify coherent structures.
- Studied the distribution of energy transfers across scales.
Main Results:
- Velocity increments show nearly Gaussian distributions in the inverse energy cascade regime.
- In the condensation regime, PDFs of velocity increments are non-Gaussian and scale-invariant.
- Coherent structures (long-lived vortices) are prominent in both regimes.
- Non-Gaussianity in the condensation regime is linked to large-scale structures.
Conclusions:
- Intermittency, in the conventional sense, is largely absent in the condensation regime of 2D turbulence.
- Large-scale coherent structures are a key factor driving non-Gaussian statistics in the condensation regime.
- The findings provide insights into the statistical nature of two-dimensional turbulent flows.