Effects of Polymer Additives on Intermittency in Forced Homogeneous Isotropic Turbulence

The drag-reducing phenomenon in forced homogeneous isotropic turbulence (FHIT) with polymer additives was realized in large eddy simulation (LES) results, which causes the variation of turbulent characteristics. Study on intermittency of turbulence is of great importance in investigating turbulent drag-reduction mechanism, because the intermittency has close relationship with coherent structures (CSs) and the transfer of energy in turbulent flows. In the present work, the influences of polymers on intermittency in FHIT were analyzed in detail by extracting CSs, researching the flatness factor based on high-order correlation function of velocity derivative and wavelet transform, surveying local intermittence measure, and discussing four rotational invariants consisting of velocity-strain tensor and vorticity tensor. From the viewpoint of the results, it can be perceived that the intermittency occurs in both the Newtonian fluid and polymer solution flows; moreover polymer additives behave inhibitive effect on the intermittency in turbulent drag-reducing flows.