Fluid acceleration in the bulk of turbulent dilute polymer solutions

Abstract

We studied the effects of long-chain polymers on the small scales of turbulence by experimental measurements of Lagrangian accelerations in the bulk of turbulent flows of dilute polymer solutions. Lagrangian accelerations were measured by following tracer particles with a high-speed optical tracking system. We observed a significant decrease in the acceleration variance in dilute polymer solutions as compared with in pure water. The shape of the normalized acceleration probability density functions, however, remained the same as in Newtonian water flows. We also observed an increase in the turbulent Lagrangian acceleration autocorrelation time with polymer concentration. The decrease of acceleration variance and the increase of acceleration autocorrelation time are consistent with a suppression of viscous dissipation, and cannot be explained by a mere increase of effective viscosity due to the polymers.