Helicity and dissipation correlation in anisotropic turbulent flow fields

Abstract

The relation between the helicity and the rate of dissipation of turbulent kinetic energy in turbulent flows has been a matter of debate. Herein, direct numerical simulations of turbulent Poiseuille and Couette flow were used in combination with the tracking of helicity, helicity density, and dissipation along the trajectories of passive scalar markers to probe the correlation between helicity and dissipation in anisotropic turbulence. The Schmidt number of the scalar markers varied between 0.7, 6, and infinite (i.e., fluid particles), while the friction Reynolds number for both simulations was 300. The probing tools were the autocorrelation coefficients, the cross correlation coefficients between helicity and dissipation, and the joint probability density function calculated in the Lagrangian framework along the positions of the scalar markers. These 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. In addition, conditional statistics for scalar markers that dispersed most or least in the flow field were also calculated. It was found that helicity and dissipation changed along the trajectories of scalar markers; however, helicity and dissipation were not correlated in the Lagrangian framework. There was anticorrelation between helicity and dissipation in the near wall region, which was less obvious in the logarithmic region. More importantly, helicity could be used to characterize the alignment of the fluctuating velocity and vorticity vectors along the trajectories of scalar markers that disperse the farthest in the direction normal to the channel wall.