Spectral analyses of high Prandtl number stratified turbulence

Abstract eng:
Spectra of decaying turbulence in a stratified fluid containing either an active (density stratifying) or a passive high Prandtl number scalar are investigated by direct numerical simulations. When the fluid is stratified by a low-Prandtl-number active scalar (P rT = 1) and simultaneouly contains a high-Prandtl-number passive scalar (P rS = 25), spectrum of the high-Prandtl-number passive scalar variance obeys the usual Batchelor scaling. On the other hand, when the fluid is stratified by a high-Prandtl-number active scalar (P rT = 25), horizontal spectrum of that active scalar (or potential energy) decreases rapidly at high wavenumbers to approach the kinetic energy spectrum, indicating the deviation from the Batchelor scaling. Examination of the spectral budget shows that the deviation is due to the persistent conversion from the potential energy to the kinetic energy at small scales.

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