Turbulence

Turbulence

2019 | V. Montagud-Camps
Homogeneous turbulence refers to fluid turbulence where space is homogeneous and isotropic, meaning no preferred direction or location. It exhibits two main characteristics: (i) energy (or related quantities) flow from large to small scales, known as direct cascade; and (ii) systematic randomness that prevents exact analytic solutions, requiring statistical descriptions, similar to thermodynamic equilibrium. Shock formation is a simplified model of turbulence, illustrated by the 1D compressible Navier-Stokes equations. Initially, a smooth cosine profile evolves into a shock with a steep gradient. Over time, higher harmonics grow, energy spectra change, and kinetic energy distributes across various wave numbers. Initially concentrated on a single wavenumber, energy spreads due to nonlinear advection. While total kinetic energy remains roughly constant initially, it begins to decrease after shock formation, reflecting turbulent dissipation. This process mirrors turbulent dissipation, where energy is distributed across scales, including dissipation scales where viscous effects dominate. The evolution shows how energy cascades from large to small scales, leading to complex, random behavior characteristic of turbulence.Homogeneous turbulence refers to fluid turbulence where space is homogeneous and isotropic, meaning no preferred direction or location. It exhibits two main characteristics: (i) energy (or related quantities) flow from large to small scales, known as direct cascade; and (ii) systematic randomness that prevents exact analytic solutions, requiring statistical descriptions, similar to thermodynamic equilibrium. Shock formation is a simplified model of turbulence, illustrated by the 1D compressible Navier-Stokes equations. Initially, a smooth cosine profile evolves into a shock with a steep gradient. Over time, higher harmonics grow, energy spectra change, and kinetic energy distributes across various wave numbers. Initially concentrated on a single wavenumber, energy spreads due to nonlinear advection. While total kinetic energy remains roughly constant initially, it begins to decrease after shock formation, reflecting turbulent dissipation. This process mirrors turbulent dissipation, where energy is distributed across scales, including dissipation scales where viscous effects dominate. The evolution shows how energy cascades from large to small scales, leading to complex, random behavior characteristic of turbulence.
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