Flow regimes of a neutrally buoyant suspension in the wake of a circular cylinder

While the rheology of suspensions has been mainly studied in the Stokes regime, fluid mechanical applications such as blood flows or sediment transport at finite particle Reynolds number require a more general understanding. From this perspective, we revisit experimentally the well-known flow around a cylinder, considering a neutrally-buoyant suspension instead of a pure fluid. Varying the particle Reynolds number, $Re$, and the solid volume fraction, $\phi$, we investigate various wake structures, from the laminar creeping flow to the Karman vortex street. We characterize the corresponding stability map as a function of $Re$ and $\phi$. The presence of particles affects the shape of the wake of the cylinder in a non-trivial way, which cannot be accounted for by a modification of the effective fluid viscosity due to particle loading. Furthermore, the presence of the particles alters the critical values of the Reynolds number at which transitions in the flow regimes occur. These results can also be interpreted by the local behavior of the particles relative to the fluid near specific features of the flow around the cylinder.