Direct Numerical Simulations of Small Particles in Wall-Bounded Turbulence*

Wall-bounded turbulence is characterized by hairpin-like structures near the wall. These structures are known to increase skin friction drag, so one method of drag reduction is to disrupt these structures using, for example, polymer additives or microbubbles. The current study seeks to find out how very small particles (on the order of the Kolmogorov scale) which release polymer behave near these structures to determine if there is an optimal particle one can design to target them. We have performed direct numerical simulations of various particles in a turbulent channel flow to better understand their clustering properties. The flow is simulated using a pseudo-spectral solver, and the particles are modeled as massless point particles using modified Maxey-Riley equations. The flow is driven by a constant pressure gradient with no gravity in order to figure out if certain particles are preferentially drawn to hairpin vortices found in turbulent wall-bounded flows. Hairpin vortex locations—identified by the λ-2 criterion—are correlated with particle locations to show the capturing capabilities by these structures.