On dissipation time scales of the basic second-order moments: the effect on the Energy and Flux-Budget (EFB) turbulence closure for stably stratified turbulence

TL;DR

This paper uses DNS data to evaluate dissipation rates of second-order moments and revises the EFB turbulence closure for stably stratified turbulence, highlighting feedback mechanisms and limitations of down-gradient transport.

Contribution

It introduces revised closure hypotheses based on DNS results and explains the feedback between TKE, buoyancy flux, and TPE in stable turbulence.

Findings

Revised EFB closure improves turbulence modeling accuracy.

Identified limitations of down-gradient transport in stable stratification.

Demonstrated feedback mechanisms maintaining turbulence at various Richardson numbers.

Abstract

The dissipation rates of the basic second-order moments are the key parameters playing a vital role in turbulence modelling and controlling turbulence energetics and spectra and turbulent fluxes of momentum and heat. In this paper, we use the results of direct numerical simulations (DNSs) to evaluate dissipation rates of the basic second-order moments and revise the energy and flux budget (EFB) turbulence closure theory for stably stratified turbulence. We delve into the theoretical implications of this approach and substantiate our closure hypotheses through DNS data. We also show why the concept of down-gradient turbulent transport becomes incomplete when applied to the vertical turbulent flux of potential temperature under stable stratification. We reveal essential feedback between the turbulent kinetic energy (TKE), the vertical turbulent flux of buoyancy, and the turbulent potential energy (TPE), which is responsible for maintaining shear-produced stably stratified turbulence for any Richardson number.