Helicity and rate of turbulent kinetic energy dissipation in a Lagrangian framework.

The relation between the helicity and the dissipation of turbulent kinetic energy in turbulent flows has been a matter of debate. In this study, Direct Numerical Simulations (DNS) of turbulent Poiseuille and Couette flow were used in combination with Lagrangian Scalar Tracking (LST) at Schmidt numbers of 0.7, 6 and infinite (i.e., fluid particles) to probe the correlation between helicity of the fluctuating velocity field and the dissipation. The 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 autocorrelation coefficients, the cross-correlation coefficients and the joint probability density function were employed to investigate the relation between helicity and dissipation along the trajectories of the Lagrangian scalar markers. There was anticorrelation between helicity and dissipation in the near wall region, which was less obvious in the logarithmic region. Helicity was found to characterize flow structures that contribute to the dispersion of scalar markers.