The validity of the Taylor frozen flow hypothesis in a chaotic flow of a dilute polymer solution in a regime of elastic turbulence is investigated experimentally. By accurate time-dependent measurements of the flow field we study the velocity coherence between pairs of points displaced both in time and space and quantify the degree of applicability of the Taylor hypothesis. Alternatively, the frozen flow assumption is assessed by comparison of the

We investigate experimentally the statistics of a chaotic flow of a dilute polymer solution in a regime of elastic turbulence by using the Lagrangian coordinates approach. We show that due to flow smoothness at small scales the Finite Time Lyapunov Exponent (FTLE) technique can be successfully used to investigate the statistics of particle pair separations at different scales. We compare the measured FTLE with the characteristics of statistical description

The onset of the {em wave resistance}, via generation of capillary gravity waves, of a small object moving with velocity $V$, is investigated experimentally. Due to the existence of a minimum phase velocity $V_c$ for surface waves, the problem is similar to the generation of rotons in superfluid helium near their minimum. In both cases waves or rotons are produced at $V>V_c$ due to {em Cherenkov radiation}. We find that the transition to the wave

The onset of the wave resistance via the generation of capillary-gravity waves by a small object moving with a velocity V is investigated experimentally. Due to the existence of a minimum phase velocity Vc for surface waves, the problem is similar to the generation of rotons in superfluid helium near their minimum. In both cases, waves or rotons are produced at V>Vc due to Cherenkov radiation. We find that the transition to the wave drag state is

The existence of internal viscoelastic waves below the elastic instability threshold in the circular Couette flow of a polymer solution is predicted. We present results of calculations of the dispersion relation of the waves. These weakly attenuating waves are sustained by a nonuniform elastic stress distribution and should occur in the region of stable stratification of the hoop elastic stresses in any viscoelastic fluid flow with curvilinear trajectories.

Microscopic flows are almost universally linear, laminar, and stationary because the Reynolds number, Re, is usually very small. That impedes mixing in microfluidic devices, which sometimes limits their performance. Here, we show that truly chaotic flow can be generated in a smooth microchannel of a uniform width at arbitrarily low Re, if a small amount of flexible polymers is added to the working liquid. The chaotic flow regime is characterized

By using high molecular weight fluorescent passive tracers with different diffusion coefficients and by changing the fluid velocity we study the dependence of a characteristic mixing length on the Peclet number, Pe, which controls the mixing efficiency. The mixing length is found to be related to Pe by a power law, Lmix / Pe0:260:01, and increases faster than expected for an unbounded chaotic flow. The role of the boundaries in the mixing length