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    A modification of the convective constraint release mechanism in the molecular stress function model giving enhanced vortex growth

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    Publication date
    2006
    Author
    Olley, Peter
    Wagner, M.H.
    Keyword
    Molecular Stress Function
    Simulation
    Convective Constraint Release
    Vortex Growth
    Opening Angle
    Rights
    © 2006 Elsevier. Reproduced in accordance with the copyright holder's self-archiving policy.
    Peer-Reviewed
    Yes
    
    Metadata
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    Abstract
    The molecular stress function model with convective constraint release (MSF with CCR) constitutive model [J. Rheol. 45 (2001), 1387] is capable of fitting all viscometric data for IUPAC LDPE, with only two adjustable parameters (with difference found only on reported ¿steady-state¿ elongational viscosities). The full MSF with CCR model is implemented in a backwards particle-tracking implementation, using an adaptive method for the computation of relative stretch that reduces simulation time many-fold, with insignificant loss of accuracy. The model is shown to give improved results over earlier versions of the MSF (without CCR) when compared to well-known experimental data from White and Kondo [J. non-Newt. Fluid Mech., 3 (1977), 41]; but still to under-predict contraction flow opening angles. The discrepancy is traced to the interaction between the rotational dissipative function and the large stretch levels caused by the contraction flow. A modified combination of dissipative functions in the constraint release mechanism is proposed, which aims to reduce this interaction to allow greater strain hardening in a mixed flow. The modified constraint release mechanism is shown to fit viscometric rheological data equally well, but to give opening angles in the complex contraction flow that are much closer to the experimental data from White and Kondo. It is shown (we believe for the first time) that a constitutive model demonstrates an accurate fit to all planar elongational, uniaxial elongational and shear viscometric data, with a simultaneous agreement with this well-known experimental opening angle data. The sensitivity of results to inaccuracies caused by representing the components of the deformation gradient tensor to finite precision is examined; results are found to be insensitive to even large reductions in the precision used for the representation of components. It is shown that two models that give identical response in elongational flow, and a very similar fit to available shear data, give significantly different results in flows containing a mix of deformation modes. The implication for constitutive models is that evaluation against mixed deformation mode flow data is desirable in addition to evaluation against viscometric measurements.
    URI
    http://hdl.handle.net/10454/521
    Citation
    Olley P and Wagner MH (2006) A modification of the convective constraint release mechanism in the molecular stress function model giving enhanced vortex growth.Journal of non-newtonian fluid mechanics. 135(1): 68-81.
    Link to publisher’s version
    http://dx.doi.org/10.1016/j.jnnfm.2006.01.002
    Type
    Article
    Collections
    Engineering and Informatics Publications

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