Inertial Finite-Time Lyapunov Exponent Analysis of a Turbulent Channel Flow

We investigate the dynamics of inertial particles in a turbulent channel flow, with a focus on their interaction with coherent vortical structures, which are known to increase skin-friction drag in wall-bounded turbulence. Heavy particles tend to accumulate in regions of low vorticity and high strain, whereas light particles or bubbles preferentially collect within vortices. We explore the behavior of "smart" particles containing drag-reducing polymers, designed to self-segregate into turbulent structures based on their density and release polymers that disrupt these structures, contributing to drag reduction. Using inertial finite-time Lyapunov exponent (iFTLE) analysis, we identify attracting and repelling flow features for particles of varying densities and Stokes numbers. This allows us to quantify flow and entrapment timescales and, in the future, to determine optimal release locations. The analysis is performed via post-processing of three-dimensional direct numerical simulation data, with parallel computation of iFTLE fields to reduce computational cost. Increased concentration of inertial particles with respect to vortices is observed at Stokes numbers close to unity. Light particles are trapped in the legs of hairpin vortices within approximately half a large-eddy turnover time, after which their concentration plateaus. Ongoing work seeks to elucidate the connection between entrapment dynamics and flow timescales that give rise to this saturation.