arXiv subjects

Deepak R. Tunuguntla

Publications and source records attributed to Deepak R. Tunuguntla.

2 recordsLinked to original sources

arXiv2019

Surface flow profiles for dry and wet granular materials by Particle Tracking Velocimetry; the effect of wall roughness

Two-dimensional Particle Tracking Velocimetry (PTV) is a promising technique to study the behaviour of granular flows. The aim is to experimentally determine the free surface width and position of the shear band from the velocity profile to validate simulations in a split-bottom shear cell geometry. The position and velocities of scattered tracer particles are tracked as they move with the bulk flow by analyzing images. We then use a new technique to extract the continuum velocity field, applying coarse-graining with the postprocessing toolbox MercuryCG on the discrete experimental PTV data. For intermediate filling heights, the dependence of the shear (or angular) velocity on the radial coordinate at the free surface is well fitted by an error function. From the error function, we get the width and the centre position of the shear band. We investigate the dependence of these shear band properties on filling height and rotation frequencies of the shear cell for dry glass beads for rough and smooth wall surfaces. For rough surfaces, the data agrees with the existing experimental results and theoretical scaling predictions. For smooth surfaces, particle-wall slippage is significant and the data deviates from the predictions. We further study the effect of cohesion on the shear band properties by using small amount of silicon oil and glycerol as interstitial liquids with the glass beads. While silicon oil does not lead to big changes, glycerol changes the shear band properties considerably. The shear band gets wider and is situated further inward with increasing liquid saturation, due to the correspondingly increasing trend of particles to stick together.

cond-mat.soft↗

arXiv2015

From discrete elements to continuum fields: Extension to bidisperse systems

To develop, calibrate and/or validate continuum models from experimental or numerical data, micro-macro transition methods are required. These methods are used to obtain the continuum fields (such as density, momentum, stress) from the discrete data (positions, velocities, forces). This is especially challenging for non-uniform and dynamic situations in the presence of multiple components. Here, we present a general method to perform this micro-macro transition, but for simplicity we restrict our attention to two-component scenarios, e.g. particulate mixtures containing two types of particles. We present an extension to the micro-macro transition method, called \emph{coarse-graining}, for unsteady two-component flows. By construction, this novel averaging method is advantageous, e.g. when compared to binning methods, because the obtained macroscopic fields are consistent with the continuum equations of mass, momentum, and energy balance. Additionally, boundary interaction forces can be taken into account in a self-consistent way and thus allow for the construction of continuous stress fields even within one particle radius of the boundaries. Similarly, stress and drag forces can also be determined for individual constituents of a multi-component mixture, which is essential for several continuum applications, \textit{e.g.} mixture theory segregation models. Moreover, the method does not require ensemble-averaging and thus can be efficiently exploited to investigate static, steady, and time-dependent flows. The method presented in this paper is valid for any discrete data, \textit{e.g.} particle simulations, molecular dynamics, experimental data, etc.

cond-mat.soft↗