Study of the rotational diffusivity coefficient of fibres in planar contracting flows with varying turbulence levels
2008 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, Vol. 34, no 9, 894-903 p.Article in journal (Refereed) Published
The Fokker-Planck equation is solved by describing the evolution of a 3D fibre orientation state along a planar contraction. A constant value of the effective rotational diffusion coefficient was determined for four different turbulent flow cases in planar contractions, reported experimentally in the literature. Two hypotheses for the non-dimensional rotational diffusivity are presented, each based on two different turbulent time scales, i.e. the Kolmogorov time scales and the time scale associated with large energy bearing eddies. These hypotheses are dependent on either the Reynolds number, based on the Taylor micro-scale, and/or a non-dimensional fibre length. The hypothesis, based on the assumption of long fibres, L-t/n greater than or similar to 25, compared to the Kolmogorov scale and in the limit of large Re-lambda seems to capture the basic trends presented in the literature. This hypothesis has also the feature of predicting effects of varying fibre length within certain limits. Accordingly, by modeling the variation of turbulent quantities along the contraction in a CFD analysis, local values of rotational diffusivity can be evaluated with the mentioned hypothesis, based on either Kolmogorov time scale or Eulerian integral time scale.
Place, publisher, year, edition, pages
2008. Vol. 34, no 9, 894-903 p.
Fokker-Planck equation; fibre; orientation; anisotropy; turbulence; dispersion; modelling
Other Materials Engineering
IdentifiersURN: urn:nbn:se:kth:diva-8483DOI: 10.1016/j.ijmultiphaseflow.2008.02.005ISI: 000259069300008ScopusID: 2-s2.0-47749133811OAI: oai:DiVA.org:kth-8483DiVA: diva2:13819
QC 20100812. Uppdaterad från in press till published (20100812).2008-05-162008-05-162010-08-12Bibliographically approved