Stability of viscoelastic flow past rigid and flexible square posts*

Viscoelastic fluid flow can become unstable even at infinitesimal Reynolds numbers due to a purely elastic flow instability resulting from the combination of streamline curvature and fluid elasticity at large Weissenberg numbers. We have recently shown that elastic flow instabilities can drive the motion of different flexible structures including sheets and circular cylinders. The fluctuating fluid forces exerted on the structures from the elastic flow instabilities can grow large enough to result in significant motion of the flexible structure.  Here we investigate the stability of the flow of a high molecular weight polymer solution past both a rigid and a flexible micropost with a square cross section.  We will present streak images and PIV vector fields characterizing the stability of the base flow around the rigid post and study the impact of fluid rheology and flow geometry on the nature and onset criteria of the elastic flow instability.  With the base flow established a flexible post will be mounted across the channel and the viscoelastic fluid structure interactions will be investigated to determine the oscillation frequency and amplitude and to look for a lock in behavior.