Growth of viscoelastic instabilities around linear cylinder arrays

Using a linear array of cylinders in a rectangular microchannel, the development of viscoelastic instabilities at moderate viscoelastic Mach numbers is investigated. Through both flow visualization and pressure drop measurements, instabilities in these channels are shown to start on the downstream face of a cylinder and grow upstream, eventually creating a vortex of slow moving fluid in front of the most upstream cylinder. Previously considered to be independent, it is shown that the downstream and upstream flow patterns all emerge due to the same mechanism related to the creation of secondary flow due to elastic waves. Furthermore, pressure drop measurements show that the relative importance of this phenomenon in terms of the excess pressure drop is mitigated for higher elasticity fluids.