Negative pressure in shear thickening band of a dilatant fluid

Abstract

We perform experiments and numerical simulations to investigate spatial distribution of pressure in a sheared dilatant fluid of the Taylor-Couette flow under a constant external shear stress. In a certain range of shear stress, the flow undergoes the shear thickening oscillation around 20 Hz. We find that, during the oscillation, a localized thickened band rotates around the axis with the flow. Based upon experiments and numerical simulations, we show that a major part of the thickened band is under negative pressure even in the case of discontinuous shear thickening, which indicates that the thickening is caused by Reynolds dilatancy; the dilatancy causes the negative pressure in interstitial fluid, which generates contact structure in the granular medium., then frictional resistance hinders rearrangement of the structure and solidifies the medium.

Uncovering Instabilities in the Spatiotemporal Dynamics of a Shear-Thickening Cornstarch Suspension

“…Three-dimensional simulations of dense suspensions were recently performed based on a fluid dynamics model for dilatant fluids where the inertia of the fluid plays a central role [27,46]. This approach accounts for the large and fast "shear-thickening oscillation" observed in the wide-gap Taylor-Couette flow of potato-starch suspensions [47] and predicts localized shear-thickened bands that bear negative pressures but that do not seem to organize or propagate along the vorticity direction [27].…”

“…Three-dimensional simulations of dense suspensions were recently performed based on a fluid dynamics model for dilatant fluids where the inertia of the fluid plays a central role [27,46]. This approach accounts for the large and fast "shear-thickening oscillation" observed in the wide-gap Taylor-Couette flow of potato-starch suspensions [47] and predicts localized shear-thickened bands that bear negative pressures but that do not seem to organize or propagate along the vorticity direction [27]. The case of a small-gap Taylor-Couette flow with much smaller inertia and more homogeneous shear rate and volume fraction conditions still remains to be explored numerically as well as experimentally through local wall or particle pressure measurements [48][49][50].…”

“…For instance, it is unclear whether particle migration, free-surface instability, vorticity shear banding, and/or gradient shear banding are at play [26][27][28], and whether the instability involves truly chaotic dynamics [20,29] as contained in early phenomenological models [30,31]. Therefore, a full spatiotemporal picture of such unstable flows is required from experiments that rely on sufficiently long and statistically stationary measurements.…”

Constitutive relation for the system-spanning dynamically jammed region in response to impact of cornstarch and water suspensions

“…The corresponding stress-strain curve exhibits a gradual increase in stress without a delay, and the stress remains mostly lower than in the steady-state, with an occasional overshoot of the steady-state by about a factor of 2. Strong fluctuations in stress have been observed around the steady state behavior [34,35], although these have not been observed to exceed the order of magnitude of the steady-state average at the higher stress end of the shear thickening regime.…”

Density waves in shear-thickening suspensions

“…If short-range repulsive forces exist between the particles, the contacts are lubricated at low shear rate. At high shear rate, high normal stresses are developed, the repulsive forces are overcome, and the contacts are frictional leading to an increase of the viscosity (10)(11)(12)(13)(14)(15)(16)(17)(18). When strong, this effect creates a discontinuous transition that comes with complex temporal fluctuations of the macroscopic shear rate under constant applied shear stress (19).…”