Mixing of passive scalar and polymer concentration in turbulent viscoelastic planar jets and wakes analysed by direct numerical simulations

Direct numerical simulations (DNS) of spatially evolving turbulent planar jets and wakes of FENE-P viscoelastic fluids is performed in order to study the small scale mixing and large scale stirring of passive and active scalars in free turbulent viscoelastic flows. The DNS are based on a highly accurate numerical algorithm employing pseudo-spectral and 6th order compact finite differences, and the shock-capturing Kurganov-Tadmor scheme. The details of the numerical methods and code validation can be found in our previous works (Guimarães et al., J. Fluid Mech., vol. 899, 2020, p. A11; Guimarães et al., J. Fluid Mech., 2022, in press). For the non-uniform polymer concentration cases, a viscoelastic fluid issues into a Newtonian environment, while for the uniform cases the fluid is viscoelastic everywhere. We show that viscoelasticity suppresses small scale mixing, but large and intermediate scale stirring can be suppressed or enhanced depending on the fluid rheological parameters and flow region in consideration.