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Cascades transition in generalised two-dimensional turbulence
Published online by Cambridge University Press: 02 April 2025
Abstract
Generalised two-dimensional (2-D) fluid dynamics is characterised by a relationship between a scalar field $q$, called generalised vorticity, and the stream function
$\psi$,namely
$q = (-\nabla ^2)^{\frac {\alpha }{2}} \psi$. We study the transition of cascades in generalised 2-D turbulence by systematically varying the parameter
$\alpha$ and investigating its influential role in determining the directionality (inverse, forward or bidirectional) of these cascades. We derive upper bounds for the dimensionless dissipation rates of generalised energy
$E_G$ and enstrophy
$\Omega _G$ as the Reynolds number tends to infinity. These findings corroborate numerical simulations, illustrating the inverse cascade of
$E_G$ and forward cascade of
$\Omega _G$ for
$\alpha \gt 0$, contrasting with the reverse behaviour for
$\alpha \lt 0$. The dependence of dissipation rates on system parameters reinforces these observed transitions, substantiated by spectral fluxes and energy spectra, which hint at Kolmogorov-like scalings at large scales but discrepancies at smaller scales between numerical and theoretical estimates. These discrepancies are possibly due to non-local transfers, which dominate the dynamics as we go from positive to negative values of
$\alpha$. Intriguingly, the forward cascade of
$E_G$ for
$\alpha \lt 0$ reveals similarities to three-dimensional turbulence, notably the emergence of vortex filaments within a 2-D framework, marking a unique feature of this generalised model.
- Type
- JFM Papers
- Information
- Copyright
- © The Author(s), 2025. Published by Cambridge University Press
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