Variable Viscosity Enables Energy Transfer Across Scales in Non-Newtonian Turbulent Flows
A new study using direct numerical simulations shows that in fluids with variable viscosity (non-Newtonian fluids), the viscous term can transfer energy across scales in turbulence, not just dissipate it locally as in constant-viscosity fluids. This challenges the traditional understanding that only convective forces drive energy cascade in turbulent flows. The finding has implications for modeling turbulence in complex fluids like polymers and suspensions used in industrial applications.
Researchers investigated spectral energy dynamics in turbulent flows of generalized Newtonian fluids using the Carreau constitutive model, which describes both shear-thinning and shear-thickening behaviors. Unlike constant-viscosity fluids where viscous effects purely dissipate energy locally, variable viscosity creates a nonlinear convolution product in spectral space that carries both energy transfer and dissipation components. The analysis reveals two distinct spectral regions: a dissipative zone near zero wavenumber and a transfer-like dipole structure near the original wavenumber in shear-thickening fluids. This dipole exhibits approximate antisymmetry characteristic of conservative energy transfer, demonstrating that energy cascade—traditionally attributed solely to convective nonlinearity—can arise from viscous nonlinearity. The viscous energy transfer participates in the forward cascade and dominates in the dissipation range, correlating with power-law spectral decay rather than the classical exponential cutoff observed in Newtonian fluids.
What's missing
The study's own limitations and open questions are not detailed in the abstract. Specifically, the scope of applicability (e.g., Reynolds number ranges tested, whether findings generalize beyond the Carreau model), validation against experimental data, and implications for practical turbulence modeling remain unspecified in the provided material.
What different sources said
- arXiv physicsCenter
No need to stay positive: a practical approach to direct numerical simulations of elastic turbulence
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