RESEARCH

Numerical simulation of particle breakage for wet fiber systems using discrete element method

The present project is proposed to develop a powerful in-house code involving the capabilities to simulate/study a wide range of applications in powder technology, well known as granular flows. All features related to particulate solid including dry and/or wet, rigid and/or flexible, unbreakable and/or breakable capabilities are covered in the unique developed code. Followings are simulation examples showing the developed features and their combination.

Video 1: Wet flexible fibers (left) vs. Dry flexible fibers (right) in a 3D shear cell

Video 2: Packing of dry deformable elongated particles (fibers) in a cylindrical container

Video 3: Breakage of dry deformable elongated particles during compaction

• N. Thai-Quang, Y. Guo, C. Wassgren, B. Hancock, W. Ketterhagen, A. Sarkar, J. Curtis (2015, February 10-12): Towards simulating breakage of wet fiber systems. CPaSS Spring 2015 IAB Meeting, University of Florida, Gainesville, Florida, United States.

Particulate suspension in bi-sliding periodic domain

Video 1: Drafting-kissing-tumbling of two settling particles in a closed box filled by fluid - Vorticity

• N. Thai-Quang, N. Mai-Duy, C.-D. Tran, T. Tran-Cong (2014): A direct forcing immersed boundary-compact integrated radial basis function approach for fluid-solid interactions in particulate fluids. Submitted to supervisors.

Heat transfer and fluid flow simulations by integrating compact integrated-RBFs scheme into direct forcing immersed boundary method

In this work, we present a numerical scheme, based on the direct forcing immersed boundary (DFIB) approach and compact integrated radial basis function (CIRBF) approximations, for solving the Navier-Stokes equations in two dimensions. The problem domain of complicated shape is embedded in a Cartesian grid containing Eulerian nodes. Non-slip conditions on the inner boundaries, represented by Lagrangian nodes, are imposed by means of the DFIB method, in which a smoothed version of the discrete delta functions is utilised to transfer the physical quantities between two types of nodes. The velocities and pressure variables are approximated locally on Eulerian nodes using 3-node CIRBF stencils, where first- and second-order derivative values of the field variables are also included in the RBF approximations. The present DFIB-CIRBF scheme is verified through the solution of several test problems including Taylor-Green vortices, rotational flow, lid-driven cavity flow with multiple solid bodies, flow between rotating circular and fixed square cylinders, and natural convection in an eccentric annulus between two circular cylinders. Numerical results obtained using relatively coarse grids are in good agreement with available data in the literature.

Figure 1: Natural convection in an eccentric circular-circular annulus, unsymmetrical flows: Contour plots for the temperature (a) and stream function (b) fields for ε ∈ {0.25, 0.50, 0.75} (from top to bottom) and φ = −45 ◦ . Each plot contains 22 contour lines whose levels vary linearly from the minimum to maximum values.

• N. Thai-Quang, N. Mai-Duy, C.-D. Tran, T. Tran-Cong (2013): A direct forcing immersed boundary method employed with compact integrated RBF approximations for heat transfer and fluid flow problems. Computer Modeling in Engineering and Sciences (CMES), vol. 96, no. 1, pp. 49-90.

Steady/unsteady fluid flows simulations using a numerical scheme based on compact integrated-RBFs and Adams-Bashforth/Crank-Nicolson

This work presents a high-order approximation scheme based on compact integrated radial basis function (CIRBF) stencils and second-order Adams–Bashforth/Crank–Nicolson algorithms for solving time-dependent problems in one and two space dimensions. We employ CIRBF stencils, where the RBF approximations are locally constructed through integration and expressed in terms of nodal values of the function and its derivatives, to discretise the spatial derivatives in the governing equation. We adopt the Adams–Bashforth and Crank–Nicolson algorithms, which are second-order accurate, to discretise the temporal derivatives. The performance of the proposed scheme is investigated numerically through the solution of several test problems, including heat transfer governed by the diffusion equation, shock wave propagation and shock-like solution governed by the Burgers' equation, and torsionally oscillating lid-driven cavity flow governed by the Navier–Stokes equation in the primitive variables. Numerical experiments show that the proposed scheme is stable and high-order accurate in reference to the exact solution of analytic test problems and achieves a good agreement with published results for other test problems.

Figure 1: Torsionally oscillating lid-driven cavity flow, 129 × 129: Evolution

of streamlines during a half-cycle of the lid motion at Re = 1000 and ω = 1.

• N. Thai-Quang, K. Le-Cao, N. Mai-Duy, C.-D. Tran, T. Tran-Cong (2013): A numerical scheme based on compact integrated-RBFs and Adams-Bashforth/Crank-Nicolson algorithms for diffusion and unsteady fluid flow problems. Engineering Analysis with Boundary Elements, vol. 37, no. 12, pp. 1653-1667.

• N. Thai-Quang, N. Mai-Duy, C.-D. Tran, T. Tran-Cong (2012): High-order alternating direction implicit method based on compact integrated-RBF approximations for unsteady/steady convection-diffusion equations. Computer Modeling in Engineering and Sciences (CMES), vol. 89, no. 3, pp. 189-220.

• N. Thai-Quang, K. Le-Cao, N. Mai-Duy, T. Tran-Cong (2012): A high-order compact local integrated-RBF scheme for steady-state incompressible viscous flows in the primitive variables. Computer Modeling in Engineering and Sciences (CMES), vol. 84, no. 6, pp. 528-557.

• N. Thai-Quang, K. Le-Cao, N. Mai-Duy, T. Tran-Cong (2011): Discretisation of the velocity-pressure formulation with integrated radial-basis-function networks. Structural Longevity, vol. 6, no. 2, pp. 77-92.

Cavitating flows in centrifugal pump using 2D cascade approach

A CFD code with 2-D cascade model was developed to predict the cavitation behavior around the impeller blades of impeller in a centrifugal pump. The governing equations are the two-phase Reynolds Averaged Navier-Stokes equations in a homogeneous form in which both liquid and vapor phases are treated as incompressible fluid. To close the model, a standard k-ɛ turbulence model is introduced. And the mass transfer rates between liquid and vapor phases are implemented as well. The validations are carried out by comparing with reference data in impeller of a centrifugal pump impeller. The cavitation characteristics of current centrifugal pumps is tested at an ondesign point (V=8 m/s) and two off-design points (V=20 m/s and V=30 m/s), respectively. The criteria of cavitation and flow instability around blades are presented. The results show that the current centrifugal pump can safely operate without cavitation at on-design point. Also, the simulation shows cavitation develops inhomogeneously among the blades at off-design points. Moreover, the effects of additional blades in the impeller are studied as well. From the numerical results, it is expected that a half-length blade is the optimum configuration as additional blades in cavitation point of view.

• Quangnha Thai, Changjin Lee (2010): The cavitation behavior with short length blades in centrifugal pump. Journal of Mechanical Science and Technology, vol. 24, no. 10, pp. 2007-2016.

• Quangnha Thai, Changjin Lee (2009): Cavitation in fuel pump with 2D cascade modeling. Journal of the Korean Society for Aeronautical and Space Sciences, vol. 37, no. 5, pp. 483-489.