Experimental study on symmetry breaking in a swirling free-surface cylinder flow influenced by viscoelasticity

In this study, we have investigated the influence of viscoelasticity on symmetry breaking of swirling cylinder flows with free surface driven by the constant rotation of bottom wall. Particle-image velocimetry was used to measure the in-plane velocity field in the meridional plane and horizontal planes at different heights for a constant aspect ratio (H/R = 2) cylinder flow. The tested fluids were water and aqueous solutions of CTAC/NaSal (CTAC - cetyltrimethyl ammonium chloride; NaSal - sodium salicylate) with 30 ppm (ppm - part per million), 100 ppm and 200 ppm weight concentration of CTAC. For water and 30 ppm CTAC solution (with very weak viscoelasticity) flows, symmetry breaking at the state of azimuthal rotating waves occurred from an onset Reynolds number. For 100 ppm and 200 ppm CTAC solutions (with relatively strong viscoelasticity), the flow never became steady at the presently measured conditions: Reynolds number ranging from 750 to 4000 and Wessenberg number ranging from 0.25 to 2.20; no organized vortex structures and clear symmetry-breaking mode as appeared in water flow were observed. If any, the symmetry breaking influenced by relatively strong viscoelasticity was in a random mode.