ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Databases for a turbulent boundary layer at Rθ=2685, a turbulent two-stream mixing layer at Rθ=5800, and a turbulent grid flow at RM=23 400 have been examined for properties of the relative helicity density, h=(U⋅Ω)/||U||||Ω||. The velocity and vorticity vectors U and Ω were simultaneously measured in these flows using a miniature probe with nine hot-wire sensors with a spatial resolution of a few Kolmogorov microscales. The results of this analysis are in generally good agreement with a similar analysis of a direct numerical channel flow simulation of Rogers and Moin [Phys. Fluids 30, 2662 (1987)]. The results do not support the suggestion that there is a high probability for the flows locally to achieve a Beltrami-like state with the velocity and vorticity vectors often nearly aligned. Such preferred alignment does not occur in the grid flow and only slightly occurs in regions of the shear flows where it is known that the mean velocity is somewhat aligned with coherent vortices. A joint probability analysis does provide some indication that alignment of the vectors is associated with lower turbulent kinetic energy dissipation. Residual mean helicity density, which previously has been explained by conjectured "spontaneous symmetry breaking,'' is shown here likely to be due to small measurement errors. Joint probability density plots show that the two parts of the convective acceleration term in the Navier–Stokes equation, the Lamb vector, Ω×U, and ∇[(U⋅U)/2], are highly correlated with each other and are similarly associated with the turbulent kinetic energy dissipation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.858371
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