  Two kinds of nonlinearities coexist in viscoelastic fluid flows, i.e.,
inertia and elasticity, which can engender different types of chaotic states
including IT, DRT, ET and EIT. The state of MDR, the ultimate state of DRT
induced by adding polymers to Newtonian IT, is recently regarded as EIT. This
letter quantitatively demonstrates the role of IT and EIT in DRT via the
contributions of RSS and the nonlinear part of ESS to flow drag. The nature of
DRT is re-examined in a wide range of flow conditions covering a series of flow
regimes from the onset of DR to MDR. We argue that EIT related dynamics appears
in DRT long before settling to MDR regime and competitively coexists with IT in
both spatial and temporal domain at moderate and high Re. More specifically, at
low DR condition, EIT firstly emerges close to the channel walls. With the
increase of elasticity, low-drag EIT gradually replaces high-drag IT from
channel walls to center, resulting in a drastic decrease of flow drag comparing
with IT. When EIT dynamics dominates the whole channel, MDR phenomenon is
formed. Our findings provide evidences that DRT phenomenon is the result of IT
and EIT interaction.
