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International audience ; The transition to turbulence in cylindrical pipes is still not fully understood despite extensive studiessince the Reynolds experiment in the early 1880s [1], even more for non-Newtonian fluids, see recentreviews [2,3]. We focused here on the mechanism leading to the transition to turbulence in pipe for yield-stress shear-thinning fluids. This transition occurs for purely shear-dependant viscosity fluids (withoutelastic effects) due to their rheological behaviors, so called here rheo-inertial transition to turbulence. Anexperimental setup allowed us to identify flow regimes in a cylindrical pipe, by combining flow structuresvisualisations and pressure drops measurements. We observed a new regime in the rheo-inertial laminar-turbulent transition, triggered below the turbulent puffs onset. This pre-transition regime is characterisedby a flow asymmetry [4,5,6] in which its position and degree evolve with the Reynolds number [7]. Theorigin for the rheo-inertial regime stability could be due to a favourable competition between the non-linear contributions of rheological behavior and flow inertia. Beyond this regime, we quantified the pufftransit intermittence. It revealed the delay to turbulence caused by the yield stress. It also revealed for thefirst time a different rheo-inertial transitional behavior in the intermittency evolution versus Reynolds,with a smoother transition on a broader Reynolds hydrodynamical range. Finally the increasing delay tothe onset of turbulent puffs with the yield stress is highlighted.References1. O. Reynolds, Philosophical Transactions, 174, 935–982 (1883).2. B. Eckhardt, Physica A : Statistical Mechanics and its Applications, 504, 121-129 (2018).3. M. Avila, D. Barkley, B. Hof, Annual Review of Fluid Mechanics, 5, 575-602 (2022)4. M. P. Escudier, R. J. Poole, F. Presti, C. Dales, C. Nouar, C. Desaubry, L. Graham, L. Pullum, Journal ofNon-Newtonian Fluid Mechanics, 127, 143-155 (2005)5. J. Peixinho, C. Nouar , C. Desaubry, B. Th´eron, J. of Non-Newtonian Fluid ... |