Publication Date:
2009-12-10
Description:
The two-dimensional space spanned by the velocity gradient invariants Q and R is expanded to three dimensions by the decomposition of R into its strain production 1/3s ijs jks ki and enstrophy production 1/4ω iω js ij terms. The {Q; R} space is a planar projection of the new three-dimensional representation. In the {Q; sss; s} space the Lagrangian evolution of the velocity gradient tensor A ij is studied via conditional mean trajectories (CMTs) as introduced by Martn et al. (Phys. Fluids, vol. 10, 1998, p. 2012). From an analysis of a numerical data set for isotropic turbulence of Reλ ̃ 434, taken from the Johns Hopkins University (JHU) turbulence database, we observe a pronounced cyclic evolution that is almost perpendicular to the QR plane. The relatively weak cyclic evolution in the QR space is thus only a projection of a much stronger cycle in the {Q; sss;ωω s} space. Further, we find that the restricted Euler (RE) dynamics are primarily counteracted by the deviatoric non-local part of the pressure Hessian and not by the viscous term. The contribution of the Laplacian of A ij, on the other hand, seems the main responsible for intermittently alternating between low and high intensity A ij states. © 2009 Cambridge University Press.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
