Experimental observation of the origin and structure of elastoinertial turbulence

Turbulence generally arises in shear flows if velocities and hence, inertial forces are sufficiently large. In striking contrast, viscoelastic fluids can exhibit disordered motion even at vanishing inertia. Intermediate between these cases, a state of chaotic motion, elastoinertial turbulence (EIT), has been observed in a narrow Reynolds number interval. We here determine the origin of EIT in experiments and show that characteristic EIT structures can be detected across an unexpectedly wide range of parameters. Close to onset, a pattern of chevron-shaped streaks emerges in qualitative agreement with linear and weakly nonlinear theory. However, in experiments, the dynamics remain weakly chaotic, and the instability can be traced to far lower Reynolds numbers than permitted by theory. For increasing inertia, the flow undergoes a transformation to a wall mode composed of inclined near wall streaks and shear layers. This mode persists to what is known as the maximum drag reduction limit, and overall EIT is found to dominate viscoelastic flows across more than three orders of magnitude in Reynolds number.

Automated summary

Turbulence generally occurs in shear flows when velocities and inertial forces are large, but viscoelastic fluids can exhibit disordered motion even with low inertia. Elastoinertial turbulence (EIT) is observed in a narrow Reynolds number interval, showing weakly chaotic dynamics in experiments and instability at lower Reynolds numbers than predicted by theory. EIT structures can be detected in a wide range of parameters, dominating viscoelastic flows across a significant range of Reynolds numbers.