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Keywords = conformation-dependent drag

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21 pages, 2205 KB  
Article
A FENE-P kε Viscoelastic Turbulence Model Valid up to High Drag Reduction without Friction Velocity Dependence
by Michael McDermott, Pedro Resende, Thibaut Charpentier, Mark Wilson, Alexandre Afonso, David Harbottle and Gregory de Boer
Appl. Sci. 2020, 10(22), 8140; https://doi.org/10.3390/app10228140 - 17 Nov 2020
Cited by 12 | Viewed by 4124
Abstract
A viscoelastic turbulence model in a fully-developed drag reducing channel flow is improved, with turbulent eddies modelled under a kε representation, along with polymeric solutions described by the finitely extensible nonlinear elastic-Peterlin (FENE-P) constitutive model. The model performance is evaluated against [...] Read more.
A viscoelastic turbulence model in a fully-developed drag reducing channel flow is improved, with turbulent eddies modelled under a kε representation, along with polymeric solutions described by the finitely extensible nonlinear elastic-Peterlin (FENE-P) constitutive model. The model performance is evaluated against a wide variety of direct numerical simulation data, described by different combinations of rheological parameters, which is able to predict all drag reduction (low, intermediate and high) regimes with good accuracy. Three main contributions are proposed: one with a simplified viscoelastic closure for the NLTij term (which accounts for the interactions between the fluctuating components of the conformation tensor and the velocity gradient tensor), by removing additional damping functions and reducing complexity compared with previous models; second through a reformulation for the closure of the viscoelastic destruction term, Eτp, which removes all friction velocity dependence; lastly by an improved modified damping function capable of predicting the reduction in the eddy viscosity and thus accurately capturing the turbulent kinetic energy throughout the channel. The main advantage is the capacity to predict all flow fields for low, intermediate and high friction Reynolds numbers, up to high drag reduction without friction velocity dependence. Full article
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16 pages, 559 KB  
Article
Influence of Polymer Relaxation Time on the Electrospinning Process: Numerical Investigation
by Siddharth Gadkari
Polymers 2017, 9(10), 501; https://doi.org/10.3390/polym9100501 - 12 Oct 2017
Cited by 30 | Viewed by 7177
Abstract
“Electrospinnability”, or the ease with which a solution can be used to obtain bead-free uniform fibers, depends on a large number of parameters, including solution properties, process parameters and ambient conditions. In this study, the effect of the polymer relaxation time on electrospinning [...] Read more.
“Electrospinnability”, or the ease with which a solution can be used to obtain bead-free uniform fibers, depends on a large number of parameters, including solution properties, process parameters and ambient conditions. In this study, the effect of the polymer relaxation time on electrospinning of dilute polymer solutions is investigated numerically. It is shown that elastic stresses (ES) increase exponentially with the Deborah number ( D e ). For each polymer concentration there exists a critical D e below which the ES are insufficient to overcome capillary stresses (CS) and lead to the formation of beaded fibers. However, above the critical D e , there is a higher probability of the ES overcoming the CS and leading to the formation of uniform fibers. This analysis suggests the possibility of improved electrospinnability even with dilute polymer solutions, provided the relaxation time is sufficiently large. It is also found that changes in the drag coefficient due to change in the polymer conformation and self-concentration of polymer molecules would become significant for the electrospinning of polymer solutions with a longer relaxation time and high conductivity. Full article
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