# Viscoelastic fluids

Tuesday, August 3, 2010 - 9:30am - 10:00am

Denis Zorin (New York University)

Vesicles are locally-inextensible fluid membranes that can

sustain bending. We consider the dynamics of flows of

vesicles suspended in Stokesian fluids. We use a boundary

integral formulation for the fluid that results in a set of

nonlinear integro-differential equations for the vesicle dynamics.

The motion of the vesicles is determined by balancing

the nonlocal hydrodynamic forces with the elastic

forces due to bending and tension. Numerical simulations

of such vesicle motions are quite challenging. On one hand,

sustain bending. We consider the dynamics of flows of

vesicles suspended in Stokesian fluids. We use a boundary

integral formulation for the fluid that results in a set of

nonlinear integro-differential equations for the vesicle dynamics.

The motion of the vesicles is determined by balancing

the nonlocal hydrodynamic forces with the elastic

forces due to bending and tension. Numerical simulations

of such vesicle motions are quite challenging. On one hand,

Tuesday, April 13, 2010 - 3:30pm - 4:15pm

Becca Thomases (University of California)

*Keywords:*Oldroyd-B, viscoelastic, instabilities,

mixing

Wednesday, October 14, 2009 - 3:30pm - 4:10pm

Sorin Mitran (University of North Carolina, Chapel Hill)

The problem of coupling microscopic and continuum-level descriptions of

complex fluids

when the microscopic system exhibits slow relaxation times is

considered. This type of

problem arises whenever the fluid exhibits significant memory effects.

The main difficulty

in this type of multiscale computation is the initialization of

microscopic configurations and

establishing the duration of microscopic evolution that has to be

computed before a continuum

time step can be taken. Density estimation theory is applied to

complex fluids

when the microscopic system exhibits slow relaxation times is

considered. This type of

problem arises whenever the fluid exhibits significant memory effects.

The main difficulty

in this type of multiscale computation is the initialization of

microscopic configurations and

establishing the duration of microscopic evolution that has to be

computed before a continuum

time step can be taken. Density estimation theory is applied to

Wednesday, October 14, 2009 - 9:00am - 9:40am

Michael Renardy (Virginia Polytechnic Institute and State University)

Traditional hydrodynamic stability studies infer stability of a flow from

a computation of eigenvalues of the linearized system. While this is well

justified for the Navier-Stokes equations, no rigorous result along these lines

is known for general systems of partial differential equations; indeed there are

counterexamples for lower order perturbations of the wave equations. This lecture

will discuss how recent results on advective equations can be applied to creeping

a computation of eigenvalues of the linearized system. While this is well

justified for the Navier-Stokes equations, no rigorous result along these lines

is known for general systems of partial differential equations; indeed there are

counterexamples for lower order perturbations of the wave equations. This lecture

will discuss how recent results on advective equations can be applied to creeping

Tuesday, October 13, 2009 - 11:00am - 11:40am

Jonathan Rothstein (University of Massachusetts)

Under the proper conditions, surfactant molecules can self-assemble into

wormlike micelles, resembling slender rods, can entangle and impart

viscoelasticity to the fluid. The behavior of wormlike micelles solutions

is similar to that of polymer solutions. The primary difference being that,

unlike covalently bound polymers, micelles are continuously breaking and

reforming under Brownian fluctuations and the imposed shear or extensional

flow field. In this talk, we will discuss the behavior of a series of

wormlike micelles, resembling slender rods, can entangle and impart

viscoelasticity to the fluid. The behavior of wormlike micelles solutions

is similar to that of polymer solutions. The primary difference being that,

unlike covalently bound polymers, micelles are continuously breaking and

reforming under Brownian fluctuations and the imposed shear or extensional

flow field. In this talk, we will discuss the behavior of a series of

Monday, October 12, 2009 - 2:00pm - 2:40pm

Satish Kumar (University of Minnesota, Twin Cities)

This talk will provide an overview of our recent work on

amplification of disturbances in channel flows of

viscoelastic fluids. Even if a standard linear stability

(i.e., modal) analysis predicts that a particular flow is

stable, the question of the sensitivity of the flow to

various disturbances remains. If disturbances to the

linearized governing equations are sufficiently amplified

over a finite time interval, then nonlinearities may become

important and cause transition to a more complex flow state.

amplification of disturbances in channel flows of

viscoelastic fluids. Even if a standard linear stability

(i.e., modal) analysis predicts that a particular flow is

stable, the question of the sensitivity of the flow to

various disturbances remains. If disturbances to the

linearized governing equations are sufficiently amplified

over a finite time interval, then nonlinearities may become

important and cause transition to a more complex flow state.

Monday, October 12, 2009 - 11:00am - 11:40am

Antony Beris (University of Delaware)

Direct Numerical Simulations (DNS) of turbulent viscoelastic channel flows

typically generate a tremendous volume of information (terabytes per run.

Data reduction is therefore essential in order to allow for an efficient

processing of the data, let alone its preservation for future studies.

However, previous attempts, using a projection of the velocity to the top

Karhunen-Loeve (K-L) modes, failed to produce velocity fields that could

generate the DNS conformation field adequately. In an effort to rectify

typically generate a tremendous volume of information (terabytes per run.

Data reduction is therefore essential in order to allow for an efficient

processing of the data, let alone its preservation for future studies.

However, previous attempts, using a projection of the velocity to the top

Karhunen-Loeve (K-L) modes, failed to produce velocity fields that could

generate the DNS conformation field adequately. In an effort to rectify

Monday, October 12, 2009 - 9:45am - 10:25am

Radhakrishna Sureshkumar (Washington University)

Ability to manipulate equilibrium self-assembly and dynamical self-organization in nonlinear systems is of central importance to the success of many emerging technologies. This seminar will focus on flow instability and pattern formation in complex fluids, i.e., fluids with internal microstructure such as solutions/melts of polymers, surfactant/colloidal gels and suspensions.

Monday, October 12, 2009 - 9:00am - 9:40am

Susan Muller (University of California, Berkeley)

*Keywords:*Elasticity, viscoelastic instability, nonlinear transitions,

drag-reducing polymers

*Abstract:*Taylor-Couette flow (i.e., flow between concentric, rotating

cylinders) has long served as a paradigm for studies of

hydrodynamic stability. For Newtonian fluids, the rich cascade

of transitions from laminar, Couette flow to turbulent flow

occurs through a set of well-characterized flow states that

depend on the Reynolds numbers of both the inner and outer

Thursday, September 17, 2009 - 9:50am - 10:35am

Robert Owens (University of Montreal)

In this talk results of pressure gradient vs. volume flow rate calculations over a wide range of oscillatory frequencies for oscillatory tube flow of healthy human blood are performed using the non-homogeneous hemorheological model of Moyers-Gonzalez et al. [M.A. Moyers-Gonzalez, R.G. Owens, J. Fang, A non-homogeneous constitutive model for human blood. Part I. Model derivation and steady flow, J. Fluid Mech. 617 (2008) 327–354]. Results at low (2 Hz) oscillatory frequencies are shown to be in close conformity to the experimental data of Thurston [G.B.