Gautam Vatsa

The implications of shear dilatancy in slow granular flows

We first examine the velocity and density fields in a granular medium composed of polydisperse circular disks in a quasi-2D annular shear device. By video imaging the flow in the dense, slow flow regime, we extract the radial variation of the azimuthal velocity u_θ and the area fraction φ_a in the steady state. Most continuum models for slow granular flow assume the granular material to be incompressible. Our experimental results question the validity of this assumption. A recently proposed non-local continuum model by Dsouza and Nott (J. Fluid Mech., 2020) incorporates shear dilatancy (change in density due to shear). We applied the model to the problem of quasi-2D annular shear flow and found an excellent agreement between the model predictions and the experimental data. We next apply the model to the problem of a 2D plane shear in the presence of gravity and show that dilatancy in combination with gravity can lead to sustained secondary flows. Krishnaraj and Nott (Nature Communication, 2016) were the first to show this phenomenon through their discrete particle simulations. Our results are in qualitative agreement with the results of Krishnaraj and Nott.