# Laboratoire de Mécanique des Fluides et d’Acoustique - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France

## Nos partenaires

Article dans J. Fluid Mech. (2021)

## Energy balance and mixing between waves and eddies in stably stratified turbulence

Henri Lam, Alexandre Delache & Fabien Godeferd

We explore the strong stratification regime of stably stratified turbulence and the intermediate regime towards the viscosity-affected stratified state. Three-dimensional velocity-density fields from direct numerical simulations are decomposed into internal gravity waves (IGWs) and eddy motion based on Riley’s decomposition (Riley et al., AIP Conf. Proc., 76(1), 1981, pp. 79–112) extended to account for the space–time properties of waves, their modification by vertically sheared horizontal flow and the vertical mixing by eddies (Lam et al., Atmosphere, 11(4), 2020, p. 420). We establish the evolution equations for the IGW and eddy parts separately. Up to buoyancy Reynolds number $Re_b\sim1$, we observe a large exchange of energy that pumps energy from the IGW to eddy. For $Re_b>1$, the IGW and eddy dynamics seem to be separate and no global exchange is observed. Our decomposition enables computation of the contributions to the mixing coefficient in terms of the IGW and eddy. At the largest $Re_b$ considered, the mixing due to eddies is four times that due to waves.