(518e) Helicity and Coherent Structures in Turned to Channel FLOW through Lagrangian Computations.

Helicity is important for understanding the relationship between coherent structures and turbulent kinetic energy. There has been an argument that coherent structures at different scales are associated with regions in which helicity is large and dissipation is low. Low dissipation means that these coherent structures could survive for a long time leading to significant impacts on the flow. In this study, direct numerical simulations of turbulent Poiseuille and Couette flow were used in combination with Lagrangian Scalar Tracking at various Schmidt number of 0.7, 6 and infinite (i.e., fluid particles), and the friction Reynolds number for both simulations was 300 to probe the correlation between helicity and dissipation, and the role of helicity in the regions of coherent structures in anisotropic turbulence. Passive scalar markers were released at different locations within the flow field, including the viscous wall sublayer, the transition layer, the logarithmic region and the outer flow. The two different flow configurations were employed in order to explore the effects of different flow structures on helicity and to investigate the possible effects of very large scale structures appearing in plane Couette flow on the correlation between helicity, dissipation and coherent structures. The autocorrelation coefficients, the cross-correlation coefficients and the joint probability density function are employed to investigate the relation between helicity to dissipation and helicity to vorticity, vertical velocity in Lagrangian frame. In addition, conditional statistics for scalar markers are evaluated in flow regions of high dissipation or coherent structure regions based on vortex identification criteria. On the other hand, scalar markers that dispersed most or least in the flow field were also calculated to provide more evidence for the role of helicity in transport in turbulent flow.