Investigation of intermittency in scalar mixing from concentrated sources by way of higher-order spectral moments

The effect of intermittency on scalar mixing is investigated by way of higher-order spectral moments.  The (hydrodynamic) flow under consideration is fully-developed turbulent channel flow and the scalar mixing within this flow is that generated by a concentrated line source within the flow.  In this work, direct numerical simulations were undertaken by way of a spectral method to solve the equations of conservation of mass and momentum, and the advection-diffusion equation was solved using a flux integral method (Germaine et al., J. Comput. Phys., 2013).  The intermittency of the scalar plume emitted by the concentrated line source is studied by way of higher-order spectral moments.  Particular attention is paid to third- and fourth-order spectral moments, using the definitions formalized by Antoni (Mech. Syst. Signal Process., 2006).  Such statistics are sensitive to transients / non-stationarities, and thus provide insight into the intermittency of the scalar field.