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

We investigate the dynamics of inertial particles in a turbulent channel flow. Coherent vortical structures are known to increase the skin-friction drag in wall bounded turbulence. It is also known that heavy particles collect in regions of low vorticity and high strain rate whereas light particles or bubbles accumulate in vortices. We intend to study the dynamics of smart particles containing drag reducing polymers. These particles would segregate themselves into coherent turbulent structures based on their density and release a polymer disrupting these structures and contributing to overall drag reduction. We use inertial finite-time Lyapunov exponents (iFTLE) analysis to identify the attracting and repelling fluid structures for particles of varying densities and Stokes numbers, attempt to determine optimal locations for their release and quantify the entrapment timescales. The analysis is carried out as a post-processing of three-dimensional direct numerical simulation (DNS) results of a turbulent channel flow and the iFTLE analysis is done in parallel to reduce computational time. Preliminary results on an analytical double-gyre flow show good agreement with literature. Preferential concentration of light particles in the vortical structures of the turbulent channel at Re_τ=180 has also been observed for tests carried out on two-dimensional slices of the DNS data.