Cross-helicity in rotating homogeneous shear-stratified turbulence.
We consider homogeneous shear-stratified turbulence in a rotating frame, that exhibits complex nonlinear dynamics. Since the analysis of relative orientation between coupled fluctuating fields helps us to understand turbulence dynamics, we focus on the alignment properties of both the velocity and gravity fields with the potential vorticity gradient. With the help of statistical mechanics, we define a vector field which plays a role in the analogous so-called cross-helicity in magnetohydrodynamics. High-resolution direct numerical simulations of developed homogeneous baroclinic turbulence are performed, and a detailed analysis of probability density functions for cross-helicity is provided. A net preference for positive cross-helicity is shown to be related to a new alignment mechanism. We argue that the analysis of cross-helicity is crucial for understanding the dynamics of buoyancy driven flows.
Institute of Atmospheric Sciences and Climate (ISAC), Corso Fiume 4, I-10133 Torino, Italy.
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Pieri
Laboratoire de Mécanique des Fluides et d'Acoustique, École centrale de Lyon, 36 Avenue Guy de Collongue, 69134 Écully cedex, France.
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Godeferd
Laboratoire de Mécanique des Fluides et d'Acoustique, École centrale de Lyon, 36 Avenue Guy de Collongue, 69134 Écully cedex, France.
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Cambon
Laboratoire SPHYNX, CEA/IRAMIS/SPEC, CNRS URA 2464, F-91191 Gif-sur-Yvette, France.
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Dubrulle
Laboratoire SPHYNX, CEA/IRAMIS/SPEC, CNRS URA 2464, F-91191 Gif-sur-Yvette, France.
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Thalabard