Utilize este identificador para referenciar este registo: http://hdl.handle.net/10400.6/607
Título: A numerical study of steady and unsteady viscoelastic flow past bounded cylinders
Autor: Oliveira, Paulo Jorge dos Santos Pimentel de
Miranda, Amílcar I. P.
Palavras-chave: Cylinder
Unsteady flow
Elastic instability
Flow separation at Re=0
Data: 2005
Resumo: We consider two-dimensional, inertia-free, flow of a constant-viscosity viscoelastic fluid obeying the FENE-CR equation past a cylinder placed symmetrically in a channel, with a blockage ratio of 0.5. Through numerical simulations we show that the flow becomes unsteady when the Deborah number (using the usual definition) is greater than De≈1.3, for an extensibility parameter of the model of L2 = 144. The transition from steady to unsteady flow is characterised by a small pulsating recirculation zone of size approximately equal to 0.15 cylinder radius attached to the downstream face of the cylinder. There is also a rise in drag coefficient, which shows a sinusoidal variation with time. The results suggest a possible triggering mechanism leading to the steady three-dimensional Gortler-type vortical structures, which have been observed in experiments of the flow of a viscoelastic fluid around cylinders. The results reveal that the reason for failure of the search for steady numerical solutions at relatively high Deborah numbers is that the two-dimensional flow separates and eventually becomes unsteady. For a lower extensibility parameter, L2 = 100, a similar recirculation is formed given rise to a small standing eddy behind the cylinder which becomes unsteady and pulsates in time for Deborah numbers larger than De≈4.0–4.5.
URI: http://hdl.handle.net/10400.6/607
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