Structure-based transient models for scalar dissipation rate in homogeneous turbulence

摘要

We present, for the first time, transient models for scalar-dissipation rate that carry information about the morphology of the turbulence structures. The proposed models are derived from a structure-sensitized transient model for the large-scale field of enstrophy. Special attention is given to the model equation of Yoshizawa (1988), from which alternative closures for scalar-dissipation rate are derived. Assuming negligible transient variations of the turbulent anisotropies, lead to an expression similar to the one used by traditional transient models for scalar dissipation rate. To reduce model uncertainties, the turbulent scalar-flux vector and the turbulence structure tensors are obtained from the same closure models for all cases considered. The estimation performance of the models is evaluated on eight cases of deformation in both fixed and rotating frames, showing encouraging results. The proposed models achieve fair agreement with homogeneous Direct Numerical Simulations (DNS) predictions in the presence of either transverse or streamwise mean scalar gradient.