Utilize este identificador para referenciar este registo: http://hdl.handle.net/10400.6/592
Título: Bifurcation phenomena in viscoelastic flows through a symmetric 1: 4 expansion
Autor: Rocha, Gerardo N.
Poole, R. J.
Oliveira, Paulo Jorge dos Santos Pimentel de
Palavras-chave: Planar symmetric expansion
Asymmetric flow
Viscoelastic fluid
FENE–CR model
FENE–MCR model
Finite volume method
Data: 28-Abr-2010
Resumo: In this work we present an investigation of viscoelastic flow in a planar sudden expansion with expansion ratio D/d = 4. We apply the modified FENE–CR constitutive model based on the non-linear finite extensibility dumbbells (FENE) model. The governing equations were solved using a finite volume method with the high-resolution CUBISTA scheme utilised for the discretisation of the convective terms in the stress and momentum equations. Our interest here is to investigate two-dimensional steady-state solutions where, above a critical Reynolds number, stable asymmetric flow states are known to occur.We report a systematic parametric investigation, clarifying the roles of Reynolds number (0.01 < Re < 100),Weissenberg number (0 < We < 100) and the solvent viscosity ratio (0.3 < β < 1). For most simulations the extensibility parameter of the FENE model was kept constant, at a value L2 = 100, but some exploration of its effect in the range 100–500 shows a rather minor influence. The results given comprise flow patterns, streamlines and vortex sizes and intensities, and pressure and velocity distributions along the centreline (i.e. y = 0). For the Newtonian case, in agreement with previous studies, a bifurcation to asymmetric flow was observed for Reynolds numbers greater than about 36. In contrast viscoelasticity was found to stabilise the flow; setting β = 0.5 and We = 2 as typical values, resulted in symmetric flow up to a Reynolds number of about 46. We analyse these two cases in particular detail.
URI: http://hdl.handle.net/10400.6/592
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