Instabilities in the oscillatory flow of a complex fluid

Abstract

The dynamics of a fluid in a vertical tube, subjected to an oscillatory pressure gradient, is studied experimentally for both a Newtonian and a viscoelastic shear-thinning fluid. Particle image velocimetry is used to determine the two-dimensional velocity fields in the vertical plane of the tube axis, in a range of driving amplitudes from 0.8 to 2.5 mm and of driving frequencies from 2.0 to 11.5 Hz. The Newtonian fluid exhibits a laminar flow regime, independent of the axial position, in the whole range of drivings. For the complex fluid, instead, the parallel shear flow regime exhibited at low amplitudes [Torralba, Phys. Rev. E 72, 016308 (2005)] becomes unstable at higher drivings against the formation of symmetric vortices, equally spaced along the tube. At even higher drivings the vortex structure itself becomes unstable, and complex nonsymmetric structures develop. Given that inertial effects remain negligible even at the hardest drivings (Re < 10(-1)), it is the complex rheology of the fluid that is responsible for the instabilities observed. The system studied represents an interesting example of the development of shear-induced instabilities in nonlinear complex fluids in purely parallel shear flow.

Experiments on the laminar oscillatory flow of wormlike micellar solutions

“…Preliminary observations reveal that this transition is highly dependent on the rate at which the driving amplitude increases. Torralba et al (2007) showed that this instability gives rise to the formation of symmetric toroidal vortices along the tube length. The study of strong nonlinearities in the flow and the transition to more complex flows falls beyond the scope of the present investigation and will be subject of future contributions.…”

Rheological properties of graphene oxide liquid crystal

“…The mechanism for such kind of instability has not been clearly understood, however, there are few reports on the oscillatory flow induced instabilities for other colloidal systems. Torralba et al [53] have reported that oscillatory flow of the Maxwell fluid is unstable at high driving frequencies. In other report, the binary mixture under horizontal vibrations have revealed the existence of a new dynamical instability due to size segregation under oscillatory shear and its connections to pattern formation in granular flows [52].…”

Chaotic component obscured by strong periodicity in voice production system

“…It is known that real fluid is very complex, and various dynamical behaviors can be found in real fluid, including asymmetry, vortices, turbulence [22,23], bifurcation [24], and spatiotemporal chaos [25,26]. These phenomena are also components of glottal airflow [27][28][29][30][31][32][33][34][35].…”