Significant influence of fluid viscoelasticity on flow dynamics past an oscillating cylinder

Abstract

This study presents a numerical investigation of how fluid viscoelasticity influences the flow dynamics past a transversely forced oscillating cylinder in the laminar vortex shedding regime at a fixed Reynolds number of 100. In particular, we examine how fluid viscoelasticity influences the boundary between the lock-in and no lock-in zones and the associated wake topology compared to that seen in a simple Newtonian fluid. All in all, we find that the fluid viscoelasticity facilitates the synchronization of the vortex street with the cylinder motion at lower oscillation frequencies than that required for a Newtonian fluid. Consequently, the boundary of the lock-in region for a viscoelastic fluid differs from the Newtonian one and broadens in the non-dimensional cylinder oscillation amplitude and frequency plane. Furthermore, we propose that excess strain generated due to the stretching of polymer molecules in a viscoelastic fluid results in a marked difference in the wake structure from that seen in a Newtonian fluid. For a Newtonian fluid, only 2S (two single vortices) and P+S (a pair and a single vortex) vortex shedding modes are detected in the primary synchronization region. However, a 2P(two pairs of vortices) vortex mode is detected for a viscoelastic fluid in this region. We also employ the data-driven dynamic mode decomposition (DMD) reduced order modeling technique to extract and analyze underlying coherent flow structures and their associated frequencies to understand the differences in the flow dynamics of Newtonian and viscoelastic fluids past an oscillating cylinder.