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TOWARDS A STRUCTURE-BASED MODEL FOR THE PREDICTION OF PASSIVE SCALAR TRANSPORT IN HYDRODYNAMIC AND MHD TURBULENCE SHEARED IN FIXED AND ROTATING FRAMES

Stavros C. Kassinos
Department of Mechanical Engineering Stanford University Stanford, California 94305 USA; Department of Mechanical and Manufacturing Engineering, Computational Sciences Laboratory, UCY-COMPSCI University of Cyprus, Nicosia, Cyprus

Evangelos E. Akylas
Department of Civil Engineering and Geomatics, Cyprus University of Technology, P.O. Box 50329, 3603, Limassol, Cyprus

Abstrakt

Turbulence models for passive scalar transport are known to have difficulties in complex flows involving strong rotation or MHD effects. Here, we consider the transport of a passive scalar in homogeneous turbulence examined in rotating frames. We first examine the effects of system rotation in the case of decaying hydrodynamic turbulence using Rapid Distortion Theory (RDT) as a guide. It is shown that the evolution of the scalar flux is strongly influenced by the structure dimensionality of the flow, and this suggests that scalar flux models must be made structure aware. Then, using Direct Numerical Simulations (DNS), we proceed to examine the case of passive scalar transport under the influence of homogeneous MHD turbulence in a conducting fluid that is undergoing mean shear in fixed and rotating frames. It is shown that in all the cases considered here, the evolution of the scalar flux coefficients can be explained in terms of the structural information provided by the one-point structure tensors. These results provide strong support for the formulation of structure-based models for passive scalar transport.