Electroosmosis of a viscoelastic fluid over non-uniformly charged surfaces: Effect of fluid relaxation and retardation time

2020 ◽  
Vol 32 (3) ◽  
pp. 032005 ◽  
Author(s):  
Bimalendu Mahapatra ◽  
Aditya Bandopadhyay
Keyword(s):  
Viscoelastic Fluid ◽  
Retardation Time ◽  
Charged Surfaces

Near-Critical Swirling Flow of Viscoelastic Fluids in a Pipe

2002 ◽  
Author(s):  
Zvi Rusak ◽  
John A. Tichy
Keyword(s):  
Relaxation Time ◽  
Viscoelastic Fluid ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Equations Of Motion ◽  
Fluid Viscosity ◽  
Retardation Time ◽  
Flow Perturbation ◽  
Boger Fluids ◽  
Flow Inertia

The interaction between flow inertia and elasticity in high Reynolds number, axisymmetric, and near-critical swirling flows of an incompressible and viscoelastic fluid in a straight circular pipe is studied. The stresses of the viscoelastic fluid are described by the Oldroyd-B constitutive model (representing the low constant-viscosity Boger fluids). A nonlinear small-disturbance analysis is developed from the governing equations of motion in order to understand the complicated interactions between flow inertia and fluid viscosity and elasticity. The effects of the fluid viscosity, relaxation time, and retardation time on the flow development in the pipe and on the critical swirl for vortex breakdown are explored. It is found that increasing the relaxation time with other parameters being fixed increases the critical swirl for vortex breakdown whereas increasing the retardation time with other parameters being fixed decreases the critical swirl for breakdown. Also, when the relaxation and retardation times are the same the critical swirl is the same as that of a Newtonian fluid. The viscoelastic characteristic times also effect the size of the flow perturbation. These results may explain the changes in the appearance of breakdown zones as function of Reynolds numbers (swirl level) that have been recently observed in the experiments by Stokes et al. (2001) where Boger fluids were used. This work extends for the first time the theory of vortex stability and breakdown to include effects of non-Newtonian fluids.

Existence and stability of steady flows of weakly viscoelastic fluids

1991 ◽  
Vol 119 (1-2) ◽  
pp. 137-158 ◽  
Author(s):  
Colette Guillopé ◽  
Jean-Claude Saut
Keyword(s):  
Constitutive Equation ◽  
Steady Flow ◽  
Linear Stability ◽  
Viscoelastic Fluid ◽  
Viscoelastic Fluids ◽  
Steady Flows ◽  
Retardation Time ◽  
Newtonian Flow ◽  
Existence And Stability ◽  
Stable Flow

SynopsisWe consider steady flows of viscoelastic fluids for which the extrastress tensor is given by a differential constitutive equation and is such that the retardation time is large (weakly viscoelastic fluids).We show the existence of a unique viscoelastic steady flow close to a given Newtonian flow and investigate its linear stability.As an example, we consider the Bénard problem for viscoelastic fluids and we prove that there exists a nontrivial linearly stable flow of a weakly viscoelastic fluid in a container heated from below.

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