Buoyancy driven turbulence and distributed chaos

TL;DR

This paper investigates various forms of buoyancy-driven turbulence, revealing how different physical conditions lead to distinct spectral behaviors characterized by stretched exponential spectra with varying beta values.

Contribution

It identifies and explains the diverse types of distributed chaos in buoyancy-driven turbulence through analysis of simulations, experiments, and atmospheric data, highlighting the role of boundary conditions and wave effects.

Findings

Stable stratification often exhibits $eta=1/3$ due to helicity.

Horizontal velocity dominated by diffusive processes with $eta=2/3$.

Boundary effects can induce $eta=1/2$ in vertical velocity spectra.

Abstract

It is shown, using results of recent direct numerical simulations, laboratory experiments and atmospheric measurements, that buoyancy driven turbulence exhibits a broad diversity of the types of distributed chaos with its stretched exponential spectrum $\exp(-k/k_{\beta})^{\beta}$. The distributed chaos with $\beta = 1/3$ (determined by the helicity correlation integral) is the most common feature of the stably stratified turbulence (due to the strong helical waves presence). These waves mostly dominate spectral properties of the vertical component of velocity field, while the horizontal component is dominated by the diffusive processes both for the weak and strong stable stratification ($\beta =2/3$). For the last case influence of the low boundary can overcome the wave effects and result in $\beta =1/2$ for the vertical component of the velocity field (the spontaneous breaking of the space translational symmetry - homogeneity). For the unstably stratified turbulence in the Rayleigh-Taylor mixing zone the diffusive processes ($\beta =2/3$) are the most common dominating processes in the anisotropic chaotic mixing of the two fluids under buoyancy forces. The distributed chaos in Rayleigh-B\'{e}nard turbulent convection in an upright cell is determined by the strong confinement conditions. That is: the spontaneous breaking of the space translational symmetry (homogeneity) by the finite boundaries ($\beta = 1/2$) or by the non-perfect orientation of the cell along the buoyancy direction ($\beta =4/7$). In all types of turbulence appearance of an inertial range of scales results in deformation of the distributed chaos and $\beta =3/5$.