Robert Poole - Fellow, Elected 2026

Prof. Rob Poole has made significant scientific contributions to the field of rheology and has been a leader in our community. Rob has been a council member of the British Society of Rheology (2009-2018) and serves as President of that organization (2025-2027). He was one of three lead organizers for the AERC meeting held in Leeds (UK) in 2024. Since 2019, Rob has been co-Editor in Chief of the Journal of Non-Newtonian Fluid Mechanics. One of the hallmarks of Rob’s scientific work is the combination of experimental, numerical, and theoretical approaches to rheology. Rob is well-known in the field of non-Newtonian fluid mechanics and for his work on purely elastic instabilities and turbulence.

Purely elastic instabilities, drag reduction, and elastic turbulence: At low Reynolds (Re) numbers, instabilities can arise in complex fluids that are totally absent in the corresponding low Re flow of Newtonian fluids. Early work was motivated by experiments from the Arratia group that showed a steady symmetry-breaking instability in a “cross-slot” geometry for a flexible polymer solution even in the limit of vanishing inertia. Rob (in collaboration with Manuel Alves and Paulo Oliveria) showed how such a symmetry-breaking bifurcation could be captured numerically with the very “simple” Oldroyd B model even in two-dimensional simulations. Subsequent numerical work showed such steady symmetry-breaking instabilities were endemic to a range of related geometries, including flow-focusing devices and the so-called “mixing separating” geometry. A taxonomy for understanding the various instabilities that can be observed in shear-dominated, extension-dominated, and “mixed” kinematics flows was published by Rob as a “Purely-Elastic Instability Flow Map” (PEFIM). More recent work on the cross-slot geometry, which combined simulations and experiments, showed how instability onset could be controlled by the addition of a cylinder at the stagnation point. This addition was especially important in understanding the root cause of the instability, as its introduction completely changes the dynamics of the stagnation point yet, for small enough diameters, did not affect critical conditions.

Other important work in this area, once again in collaboration with Alves but also with the Lindner group, has been undertaken on the “serpentine” channel and in particular in illustrating how instability onset, this time to a time-dependent flow, scales with the aspect ratio of the geometry, how shear thinning stabilizes the onset, and how this geometry can be used as a microfluidic rheometer for measuring relaxation times. Rob and his group also used this geometry to illustrate the significant enhancement in heat transfer that can be observed by inducing an elastic instability and then elastic turbulence. Rob’s group was also the first to use elastic turbulence to generate emulsions. Finally, by deliberately exploiting the polymer degradation observed during classical turbulent drag reduction by polymers and studying pipe, channel and square duct flows, Rob and his team were the first to tie a measurable fluid property (the “CaBER” relaxation time) to the degree of drag reduction thus allowing for an a priori quantitative prediction of drag reduction from a knowledge of polymer relaxation time, flow rate and geometric length scale.