Inward propagating chemical waves in Taylor vortices

Abstract

Advection-reaction-diffusion (ARD) waves in the Belousov-Zhabotinsky reaction in steady Taylor-Couette vortices have been visualized using magnetic-resonance imaging and simulated using an adapted Oregonator model. We show how propagating wave behavior depends on the ratio of advective, chemical and diffusive time scales. In simulations, inward propagating spiral flamelets are observed at high Damköhler number (Da). At low Da, the reaction distributes itself over several vortices and then propagates inwards as contracting ring pulses--also observed experimentally.

MRI of chemical reactions and processes

“…Since its initially contentious beginnings, this reaction has become the most studied pattern-forming reaction, and provides a useful device for observing the coupling between reaction with molecular transport [21] and other environmental factors or external stimuli [27]. The chemical waves formed in the BZ reaction, and other autocatalytic reactions, are particularly useful for characterising transport and mixing behaviour within complex flow environments [28][29][30][31][32], because only small amounts of the autocatalyst are required to enter a region, before there is a rapid amplification of the concentration of that, and associated, species.…”

“…The interplay between chemistry and flow has also been investigated in a series of counter-rotating (Taylor) vortices [29,30,85], formed in a Couette cell above a critical rotation rate. MRI has proved particularly useful for characterising the flow and intra-/intervortex mixing [93,94] characteristics for Taylor vortices, through MRI velocity and diffusion imaging ( Fig.…”

“…5(a) and (b)) and propagator measurements. When the fluid within a series of Taylor vortices is the BZ reaction, and the autocatalysis is triggered locally, a travelling chemical wave is observed, which propagates through the vortices, initially along the outer regions of each vortex, where mixing is greatest [30], before propagating inwards, into the centre of each vortex (Fig. 5(c)).…”

Front propagation in a vortex lattice: dependence on boundary conditions and vortex depth

“…Important consequences follow in the fields of combustion 1 , chemistry 2,3 or even ecology [4][5][6] . However, the actual mechanisms of front velocity enhancement as well as the whole factors on which this velocity depends call for a better understanding in both turbulent 1,[7][8][9][10][11][12] and laminar [13][14][15][16][17][18][19][20][21] contexts.…”

“…provided by neighbor vortices) and the set of separatrices was found to form a square array. In comparison, apart from a study in Taylor vortex flows 21 , experiments [18][19][20] addressed a single chain of vortices confined in a channel. Then, different boundary conditions were applied on vortex separatrices depending on whether they were a channel wall (rigid b.c.)…”