I shall describe some recent table-top experiments that we have performed in our laboratory. In the first experiment, millimeter-sized steel balls are dropped in aqueous clay suspensions. We observe that balls of larger diameters fail to achieve terminal velocity over the entire duration of the experiment. We propose a toy model that correctly predicts the time-dependence of the ball velocity for a range of ball sizes and clay concentrations. In another experiment, we record and analyze the interfacial fingering patterns that emerge when a Newtonian fluid displaces aqueous cornstarch suspensions in a radial Hele-Shaw cell. Increasing the viscosity of the displacing fluid and the concentration-dependent elasticity of the outer viscoelastic fluid both lead to significant suppression of interfacial instabilities. By performing a linear stability analysis of the interface, we predict a dominant wavelength of interfacial perturbation that closely matches with the spacing between fingers measured experimentally at the onset of instability.
Zoom link: https://zoom.us/j/92784092384?pwd=b3dDbUt6Y2M4ZmNPaVJ6aVBQbjArUT09
Meeting ID: 927 8409 2384