Emergence of transient reverse fingers during radial displacement of a shear-thickening fluid

A highly sheared dense aqueous suspension of granular cornstarch particles displays rich nonlinear rheology. We had previously demonstrated the growth and onset interfacial instabilities when shear-thinning suspensions were displaced by a Newtonian fluid, suggested methods to maximise displacement efficiency [Palak, R. Sathayanath, S. K. Kalpathy Bandyopadhyay, Colloids Surf. Physicochem. Eng. Asp., 629 (2021) 127405]. In present work, we explore miscible in its discontinuous shear-thickening regime quasi-two-dimensional radial Hele-Shaw cell. systematically study kinetics inner interface between water suspension, also outer air. addition at interface, observe transient withdrawal formation fingering interface. demonstrate that these `reverse fingering' are extremely sensitive injection flow rate water, gap cell concentration {and emerge irrespective immiscibility fluid pair. believe as dilates due high shear imposed displacing suspension-air responds with restoring force, resulting penetration air into reverse fingers. note fingers significantly reduces suspension. Finally, correlation patterns computing velocity which stresses propagate confined Our findings useful understanding materials through constrained geometries can be extended stress propagation sudden imposition rate, such impact behaviour.