scholarly journals Influence of granular temperature and grain rotation on the wall friction coefficient in confined shear granular flows

2021 ◽  
Vol 249 ◽  
pp. 03026
Author(s):  
Cheng-Chuan Lin ◽  
Riccardo Artoni ◽  
Fu-Ling Yang ◽  
Patrick Richard
Keyword(s):  
Friction Coefficient ◽  
Granular Matter ◽  
Scaling Law ◽  
Three Dimensional ◽  
Granular Flows ◽  
Force Sensor ◽  
Wall Friction ◽  
Granular Temperature ◽  
Research Perspective ◽  
Dense Granular Flows

A depth-weakening wall friction coefficient, µw, has been reported from three-dimensional numerical simulations of steady and transient dense granular flows. To understand the degradation mechanisms, a scaling law for µw/ f and χ has been proposed where f is the intrinsic particle-wall friction and χ is the ratio of slip velocity to square root of granular temperature (Artoni & Richard, Phys. Rev. Lett., vol. 115 (15), 2015, 158001). Independently, a friction degradation model has been derived which describes a monotonically diminishing friction depends on a ratio of grain angular and slip velocities, Ω (Yang & Huang, Granular Matter, vol. 18 (4), 2016, 77). In search of experimental evidence for how these two parameters degrade the µw, an annular shear cell experiment was performed to estimate the bulk granular temperature, angular and slip velocities at sidewall through image-processing. Meanwhile, µw was measured by a force sensor to confirm the weakening towards the creep zone. The measured µw/ f − χ and µw/ f − Ω were both well-fitted to the corresponding models showing that both granular temperature and angular velocity are significant mechanisms to degrade the µw which broadens the research perspective on modeling the boundary condition of dense granular flows.

scholarly journals Self-diffusion scalings in dense granular flows

Soft Matter ◽  
2021 ◽  
Author(s):  
Riccardo Artoni ◽  
Michele Larcher ◽  
James T. Jenkins ◽  
Patrick Richard
Keyword(s):  
Shear Rate ◽  
Solid Fraction ◽  
Granular Flows ◽  
The Self ◽  
Granular Temperature ◽  
Restitution Coefficient ◽  
Self Diffusion ◽  
Diffusivity Tensor ◽  
Dense Granular Flows

The self-diffusivity tensor in homogeneously sheared dense granular flows is anisotropic. We show how its components depend on solid fraction, restitution coefficient, shear rate, and granular temperature.

Discrete Element Studies of Gravity-Driven Dense Granular Flows in Vertical Cylindrical Tubes

2016 ◽  
Author(s):  
Yesaswi N. Chilamkurti ◽  
Richard D. Gould
Keyword(s):  
Granular Flows ◽  
Discrete Element ◽  
Current Paper ◽  
Wall Friction ◽  
Geometrical Parameters ◽  
Soft Particle ◽  
Flow Physics ◽  
Cylindrical Tubes ◽  
Gravity Driven ◽  
Dense Granular Flows

The current paper focusses on the characterization of gravity-driven dry granular flows in cylindrical tubes. With a motive of using dense particulate media as heat transfer fluids (HTF), the main focus was to address the characteristics of flow regimes with a packing fraction of ∼60%. In a previous work [1], experimental and computational studies were conducted to understand the effects of different geometrical parameters on the flow physics. The current paper is an extension of that work to gain more insights into the granular flow physics. The three-dimensional computer simulations were conducted by implementing the Discrete Element Method (DEM) for the Lagrangian modelling of particles. Hertz-Mindilin models were used for the soft-particle formulations of inter-particulate contacts. Simulations were conducted to examine the particulate velocities and flow rates to understand the rheology in the dense flow regime. Past studies suggested the existence of a Gaussian mean velocity profile for dense gravity-driven granular flows. These observations were further analyzed by studying the influence of geometrical parameters on the same. The current work thus focusses on studying the rheology of dense granular flows and obtaining a better understanding of the velocity profiles, the wall friction characteristics, and the particle-wall contact behavior.

scholarly journals Experimental and Computational Studies of Gravity-Driven Dense Granular Flows

2015 ◽  
Author(s):  
Yesaswi N. Chilamkurti ◽  
Richard D. Gould
Keyword(s):  
Three Dimensional ◽  
Granular Flows ◽  
Packing Fraction ◽  
Velocity Shear ◽  
Spherical Particles ◽  
Tube Length ◽  
Soft Particle ◽  
Mean Velocity ◽  
Gravity Driven ◽  
Dense Granular Flows

The current paper focusses on the characterization of gravity-driven dry granular flows in cylindrical tubes. With a motive of using dense particulate media as heat transfer fluids (HTF), the study was primarily focused to address the characteristics of flow regimes with a packing fraction of ∼60%. Experiments were conducted to understand the effects of different flow parameters, including: tube radius, tube inclination, tube length and exit diameter. These studies were conducted on two types of spherical particles — glass and ceramic — with mean diameters of 150 μm and 300 μm respectively. The experimental data was correlated with the semi-empirical equation based on Beverloo’s law. In addition, the same flow configuration was studied through three-dimensional computer simulations by implementing the Discrete Element Method for the Lagrangian modelling of particles. A soft-particle formulation was used with Hertz-Mindilin contact models to resolve the interaction forces between particles. The simulation results were used to examine the velocity, shear rate and packing fraction profiles to study the detailed flow dynamics. Curve-fits were developed for the mean velocity profiles which could be used in developing hydrodynamic analogies for granular flows. The current work thus identifies the basic features of gravity driven dense granular flows that could form a basis for defining their rheology.

scholarly journals Stability analysis of rapid granular chute flows: formation of longitudinal vortices

2002 ◽  
Vol 467 ◽  
pp. 361-387 ◽  
Author(s):  
YOËL FORTERRE ◽  
OLIVIER POULIQUEN
Keyword(s):  
Stability Analysis ◽  
Kinetic Theory ◽  
Three Dimensional ◽  
Granular Flows ◽  
Granular Temperature ◽  
Instability Mechanism ◽  
Longitudinal Vortices ◽  
Spontaneous Formation ◽  
Wide Range ◽  
Inclined Planes

In a recent article (Forterre & Pouliquen 2001), we have reported a new instability observed in rapid granular flows down inclined planes that leads to the spontaneous formation of longitudinal vortices. From the experimental observations, we have proposed an instability mechanism based on the coupling between the flow and the granular temperature in rapid granular flows. In order to investigate the relevance of the proposed mechanism, we perform in the present paper a three-dimensional linear stability analysis of steady uniform flows down inclined planes using the kinetic theory of granular flows. We show that in a wide range of parameters, steady uniform flows are unstable under transverse perturbations. The structure of the unstable modes is in qualitative agreement with the experimental observations. This theoretical analysis shows that the kinetic theory is able to capture the formation of longitudinal vortices and validates the instability mechanism.

scholarly journals Compressibility regularizes the 𝜇(I)-rheology for dense granular flows

2017 ◽  
Vol 830 ◽  
pp. 553-568 ◽  
Author(s):  
J. Heyman ◽  
R. Delannay ◽  
H. Tabuteau ◽  
A. Valance
Keyword(s):  
Friction Coefficient ◽  
Acoustic Waves ◽  
Compressible Flows ◽  
Granular Flows ◽  
Potential Candidate ◽  
Volume Changes ◽  
Ill Posed ◽  
The Stability ◽  
Well Posed ◽  
Dense Granular Flows

The $\unicode[STIX]{x1D707}(I)$-rheology was recently proposed as a potential candidate to model the incompressible flow of frictional grains in the dense inertial regime. However, this rheology was shown to be ill-posed in the mathematical sense for a large range of parameters, notably in the low and large inertial number limits (Barker et al., J. Fluid Mech., vol. 779, 2015, pp. 794–818). In this rapid communication, we extend the stability analysis of Barker et al. (J. Fluid Mech., vol. 779, 2015, pp. 794–818) to compressible flows. We show that compressibility regularizes the equations, making the problem well-posed for all parameters, with the condition that sufficient dissipation be associated with volume changes. In addition to the usual Coulomb shear friction coefficient $\unicode[STIX]{x1D707}$, we introduce a bulk friction coefficient $\unicode[STIX]{x1D707}_{b}$, associated with volume changes and show that the problem is well-posed if $\unicode[STIX]{x1D707}_{b}>1-7\unicode[STIX]{x1D707}/6$. Moreover, we show that the ill-posed domain defined by Barker et al. (J. Fluid Mech., vol. 779, 2015, pp. 794–818) transforms into a domain where the flow is unstable but remains well-posed when compressibility is taken into account. These results suggest the importance of taking into account dynamic compressibility for the modelling of dense granular flows and open new perspectives to investigate the emission and propagation of acoustic waves inside these flows.

High speed granular flows down inclines

2020 ◽  
Author(s):  
Zhu Yajuan ◽  
Renaud Delannay ◽  
Alexandre Valance
Keyword(s):  
High Speed ◽  
Scaling Law ◽  
Granular Flows ◽  
Side Wall ◽  
Flow Regimes ◽  
Secondary Flows ◽  
Wall Friction ◽  
Restitution Coefficient ◽  
Longitudinal Vortices ◽  
Gap Width

<p>We investigate numerically high speed granular flows down inclines. Recent numerical works have<br>highlighted that the presence of lateral frictional walls allows to produce novel Steady and Fully<br>Developed (SFD) flow regimes at high angle of inclination where accelerated regimes are usually<br>expected (Brodu et al., 2015). These SFD regimes present non-trivial features, including secondary flows<br>with longitudinal vortices and “supported“ flows characterized by a central and dense core supported by<br>a very agitated dilute layer.<br>We present a review of these new regimes and provide their domain of existence in the parameter space<br>including the mass hold-up M, the inclination angle θ and the gap width between the lateral walls. We<br>also investigate the sensitivity of these states to the mechanical parameters of particles such as the<br>restitution coefficient e for binary collisions.<br>We emphasize two salient outcomes. (I) First, our simulations reveal that the emergence of the<br>supported flows is favored by low restitution coefficient (i.e., high dissipation). Surprisingly, increasing<br>the dissipation leads to faster flows. This is explained by a contraction of the flow, resulting in a lower<br>contribution of the side-wall friction. (ii) Second, despite the diversity of the supported flow regimes, the<br>simulations bring to the light that the mass flow rate Q obeys a simple scaling law with the mass hold-up<br>and the gap width: Q~M3/4W1/4.<br>Bibliography<br>Brodu et al., 2015, Journal of Fluid Mechanics, 2015, 769, 218-228</p>

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