Effects of polymer additives on the energy injection, transfer and dissipation rates in turbulent flow*

We report an experimental study of polymer’s effect on the energy transport process in a Von Karman swirling flow system (VKS) with smooth disks. By simultaneous measurement of the torque exerted on the disks and the the three components of the velocity at the center of VKS in a plane along its diameter with high spatial resolution, we determined the energy injection, transfer and dissipation rate independently. It is found that the flow is more isotropic with polymer additives. With increasing poymer concentration, the torque decreases continuously, while the energy transfer and dissipation rate first experience a sharp and then a slow decrease. Besides, the energy dissipation rate is larger than the transfer rate, and their difference is nearly constant. We also studied the Weissenberg number （Wi） effect. It is found that the energy dissipation rate is equal to the transfer rate at small Wi, and becomes larger than the transfer rate at a critical Wi.