Asymptotic Dynamics of High Dynamic Range Stratified Turbulence

Area of Science:

• Fluid dynamics
• Turbulence research
• Stratified flow dynamics

Background:

• High dynamic range turbulence is crucial for understanding energy dissipation and mixing.
• Previous studies suggested asymptotic regimes in stratified and sheared turbulence.
• The Ozmidov and Kolmogorov scales define the dynamic range relevant to buoyancy effects.

Purpose of the Study:

• To investigate the asymptotic behavior of homogeneous sheared and stably stratified turbulence.
• To probe the high dynamic range regime (Re_b up to 1000) using direct numerical simulations.
• To isolate the influence of Re_b on irreversible mixing and energy partitioning.

Main Methods:

• Direct numerical simulations (DNS) of statistically stationary homogeneous sheared and stably stratified turbulence.
• Analysis of flow configurations spanning three decades in dynamic range.
• Evaluation of the impact of Re_b (ε/(νN²)) on turbulence characteristics.

Main Results:

• Evidence suggests an asymptotic state is reached for Re_b ⪆ 300.
• This asymptotic state is characterized by stable partitioning of potential and kinetic energies.
• Dissipation rate components approach values expected under isotropy; turbulent flux coefficient shows a slight decrease but not the Γ∝Re_b⁻¹/² dependence.

Conclusions:

• Homogeneous sheared and stably stratified turbulence exhibits an asymptotic regime at high Re_b.
• Energy partitioning and dissipation behavior in this regime are consistent with theoretical expectations.
• The commonly proposed Γ∝Re_b⁻¹/² relationship for the turbulent flux coefficient is not observed in the simulated range.