IPMI: Flow of yield stress fluids: stopping, starting and practical applications
Speaker: Ian Frigaard (University of British Columbia)
Date: April 7, 2017 10:30
Location: SP2 416-1
Yield stress fluids do not deform unless a stress threshold is exceeded, but are otherwise viscous. The presence of the yield stress significantly alters the stability properties of these flows. In the first place, many static flows which would be mechanically unstable for simpler Newtonian fluids can now be observed. These flows are found when the ratio of yield stress to driving stresses exceeds a critical value, say $Y Y_c$. Secondly, in the case that $Y Y_c$ the static flows appear to be energy stable (and globally energy stable in some cases). The critical value $Y_c$ is defined by an optimization problem that may be solved approximately by a number of methods that we outline. An interesting observation is that, when $YY_c$, as the transient velocity decays to zero the slowest decaying components of the solution resemble the minimizer that defines $Y_c$. Our intuitive interpretation of this is as a nonlinear eigenvalue problem. To illustrate the behaviour of these systems, we present examples from applications with particle motion and with buoyancy driven motion. Joint work with E. Chaparian, I. Karimfazli and A. Wachs.