Experimental observation of shear thickening oscillation

Abstract

-We report experimental observation of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. Using density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed that well-marked vibrations of the frequency around 20 Hz appear via a Hopf bifurcation upon increasing externally applied shear stress. The parameter range and the frequency of the vibration are consistent with those expected by a simple phenomenological model of the dilatant fluid.Introduction. -Dense colloids and dense granulefluid mixtures are often called dilatant fluids and known to show severe shear thickening, i.e. its viscosity changes discontinuously by orders of magnitude upon increasing the shear rate [1][2][3][4]. This is a source of a variety of unintuitive behaviors of the media [5][6][7][8], and might be used for interesting application like a body armor [9], but often causes problems in industrial situations, such as the damage of mixer motors due to overloading [1].Although the severe shear thickening is a property that can be demonstrated easily with common material like starch and water, physicists have not reached a general agreement on its microscopic mechanism. Originally, the order-disorder transition of the dispersed particles was proposed [1,[10][11][12], but later the hydrodynamics cluster formation by the lubrication force is considered to be more consistent with experimental observations and numerical simulations [13][14][15][16]. More recently, the shear thickening transition is discussed in connection with the jamming and/or the compaction of granules [17][18][19][20].Recently, the present authors constructed a phenomenological model that describes macroscopic flowing properties of a shear thickening fluid [21,22]. By analyzing the model, they pointed out that the discontinuous thickening upon increasing the shear rate signifies that the shear thickening fluid is actually shear stress thickening, not shear rate thickening because only the shear stress thickening can produce the S-shaped flow curve with an unstable

Negative pressure in shear thickening band of a dilatant fluid

“…As for the boundaries in the rotating axis direction, however, we employ the periodic boundary condition for simplicity. We set diameter of the center rod d = 2, the flow width h = 1.5 and the fluid depth ℓ = 2.6 by the units (11). With the parameters for the present medium, they are comparable with the ones for our experimental set up.…”

Kinetic theory of shear thickening for a moderately dense gas-solid suspension: From discontinuous thickening to continuous thickening

“…In addition, the normal stress difference becomes large when the shear thickening takes place [4,5]. The mechanism of the DST can also be understood by the introduction of an order parameter which exhibits a S-shape in a plane of stress-strain rate (flow curve) [16][17][18][19][20].Although most of previous studies on shear thickening are oriented to dense suspensions, it would be convenient to consider relatively low density systems where kinetic theory tools [21][22][23][24][25] can provide a deeper understanding on the microscopic mechanisms involved in the DST. Indeed, some papers have reported that a DST-like process for the kinetic temperature can take place as a result of a saddle-node bifurcation [26][27][28][29].…”

“…In addition, the normal stress difference becomes large when the shear thickening takes place [4,5]. The mechanism of the DST can also be understood by the introduction of an order parameter which exhibits a S-shape in a plane of stress-strain rate (flow curve) [16][17][18][19][20].…”

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]. 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].…”