Elasto inertia transitions in Taylor Couette flows

 

Stavroula Balabani1  & Tom Lacassagne2

1Mechanical Engineering University College London UK,

2IMT Nord Europe, University of Lille, France

 

Abstract

 

 

We present our experimental studies on elasto-inertial transitions in Taylor–Couette (TC) flows of polymer solutions. We employ solutions of polymers with different molecular weights and concentrations as well as semi dilute suspensions of particles so that we can probe the effects of elasticity, shear thinning and particulate phase on flow transitions.  We characterise these flow transitions by means of flow visualisation during ramp up, ramp down and steady state flow experiments; Particle Image Velocimetry is also used to further characterise selected flow regimes.

 

When elasticity dominates, the flow transitions from purely azimuthal Couette flow (CF) to a highly chaotic flow state referred to as elasto-inertial turbulence (EIT) via Taylor vortex flow (TVF) and elasto-inertial rotating spiral waves (RSW).  Crossing of the elastic axial waves (rotating standing waves, RSW) with Taylor vortices leads to vortex merging and splitting events; these events are random in nature, increase in frequency with Re and cause abrupt changes in the axial spatial wavelength, leading to a transition to EIT; this new mechanism to EIT occurs regardless of the existence of shear thinning. In the absence of shear thinning (Boger fluids), an increase in elasticity, alters the nature of these events to a ‘flame’ pattern formation.

 

Increasing the extent of shear thinning is found to modify, delay, or even completely suppress elasto-inertial transitions (RSW, EIT) providing thus a control mechanism to tune TC viscoelastic instabilities.  A similar stabilising mechanism is found by the addition of small particles to the polymeric fluids; the presence of particles in Boger fluids delays the transition to elasto-inertial turbulence (EIT) and alters the features of EIT.

 

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