Viscoelastic Kolmogorov Flow at Low Reynolds Number

Flow instabilities can arise in dilute polymeric solutions even in the absence of inertia. Both experimental and theoretical investigation have identified multiple physical origins for elastic instabilities across different flow conditions which may include a combination of geometry (streamline curvature) and flow types (shear, and extension). In the case of shear flows, recent numerical work has identified different mechanisms for creating purely elastic instabilities in shear flows, namely a wall-mode and a center-mode. It is thus desirable to decouple the effects of the wall from pure shear (flow) effects. In this talk, we present two experimental platforms to achieve Kolmogorov flows at different length scales: (i) a Lorentz flow cell setup and (ii) a microfluidic device. These experimental flows allow us to achieve a range of Weissenberg numbers (up to Wi=10) while keeping the Reynolds number below 1 (Re<1). Velocimetry measurements show aperiodic fluctuations from the base flow and spatial asymmetries in the viscoelastic flows that are not present in the Newtonian case.