Alignment of vorticity and scalar gradient with strain rate in simulated Navier-Stokes turbulence
The alignment between vorticity and eigenvectors of the strain-rate tensor in numerical solutions of Navier-Stokes turbulence is studied. Solutions for isotropic flow and homogeneous shear flow from pseudospectral calculations using 128(cubed) grid points were examined. The propensity for vorticity alignment with a positive intermediate strain is a consequence of angular momentum conservation, as shown by a restricted Euler model of the coupling between strain and vorticity. Probability distributions for intermediate strain, conditioned on total strain, change from a symmetric triangular form at small strain to an asymmetric one for large strain. The most-probable value of the asymmetric distribution gives strains in the ratios of 3:1 - 4. The evolution of the distribution from a symmetric to an asymmetric form as the strain magnitude increases is essentially the same in both flows, indicating a generic structure of intense turbulence. The alignment between the gradient of a passive scalar and eigenvectors of the strain-rate tensor for Prandtl numbers of 0.1, 0.2, 0.4, and 1.0 is studied. There is an increased probability for the scalar gradient to align in the most compressive-strain direction, and the average gradient is larger when it is pointing in that direction.
- Research Organization:
- National Center for Atmospheric Research, Boulder, CO (USA)
- OSTI ID:
- 7126949
- Report Number(s):
- AD-A-194011/3/XAB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
420400* -- Engineering-- Heat Transfer & Fluid Flow
ALIGNMENT
ANGULAR MOMENTUM
ASYMMETRY
DIFFERENTIAL EQUATIONS
DISTRIBUTION
EIGENVECTORS
ENERGY
EQUATIONS
FLUID FLOW
KINETIC ENERGY
MATHEMATICS
MECHANICAL PROPERTIES
NAVIER-STOKES EQUATIONS
NUMERICAL ANALYSIS
PARTIAL DIFFERENTIAL EQUATIONS
PRANDTL NUMBER
PROBABILITY
SHEAR PROPERTIES
SIMULATION
STRAIN RATE
TENSORS
TURBULENCE
VORTEX FLOW