Jieke Yao; Chengwen Zhong; Kebing Tang

An adaptive mesh refinement technique for lattice Boltzmann method (LBM) is proposed in this paper. It combines hierarchical linked-list data structure and the LBM calculation. Based on uniform meshes, the adaptive algorithm refines the meshes by constructing the linked-lists of nodes, cells and levels for mesh levels refined. To guarantee the stability of numerical scheme, quadratic bubble function for the nodal momentum is used to interpolate in the LBM calculation of different mesh levels. For the flows of relatively higher <i>Re</i>, large Eddy simulation (LES) is adopted to solve turbulence problems. Because of the use of adaptive technique, the computational time can be cut and accurate flow field information can be captured. OpenMP parallel for linked-list data structure is used to improve computational efficiency. To verify the present method, flows over circular cylinder at <i>Re</i> = 40, 300, 500, 1,000 and 3,900 and NACA0012 airfoil at <i>Re</i> = 10<SUP align=right>5</SUP> for AOA = 4° are simulated. ]]>

Saurabh Bhardwaj; Pitambar Randive; Amaresh Dalal

The present work numerically analyses the interfacial dynamics of coalescence of two droplets on a rectangular channel wall considering wetting effects. The two-phase lattice Boltzmann Shan-Chen model has been incorporated to explore the physics of coalescence of two droplets on channel wall. The main focus of the study is to analyse the time taken by the two droplets to initiate merging into a single droplet and the displacement of immiscible droplets subjected to gravitational forces. The impact of the centre distance between the two droplets (i.e., <i>C</i><SUB align="right"><i>d</i> = 47-55 <i>lu</i>) and capillary number (i.e., Ca = 0.35, 0.50 and 0.81) on droplet dynamics have been examined. The investigation revealed that the two droplets do not merge completely into a single spherical droplet in mixed wettability case but stretched at the junction of hydrophilic and hydrophobic region. It is further revealed that the two droplets coalesce faster on mixed wettable surface compared to uniform hydrophilic surface at a fixed capillary number.]]>

Evan M. Smuts; David A. Deglon; Chris J. Meyer

This paper describes the development of a numerical model used to study the rheology of particulate suspensions. A combination of computational fluid dynamics (CFD) and the discrete element method (DEM) was used to model the fluid and particulate phases, respectively. Initially, CFD models of different rheometer geometries were tested for both a Newtonian and a non-Newtonian fluid. Once the single-phase model had been validated, a coupled model combining CFD and DEM was created. This coupled model is currently capable of modelling spherical particles in a suspending liquid. DLVO forces were included to account for the surface charge on particles. Different numerical parameters were evaluated for their suitability for this problem. These parameters were used to test the models response to changes in solids volume concentration and different particle surface charge. When compared to experimental data, the model produced similar trends.]]>

Unal Akdag; Selma Akcay; Dogan Demiral

In this study, the heat transfer characteristics of CuO-water-based nanofluids in a trapezoidal-corrugated channel under pulsating inlet flow conditions are investigated numerically. The simulations are performed for different Reynolds numbers, pulsating frequencies and amplitudes via a control volume-based CFD solver. The nanoparticle volume fraction and the other parameters are kept constant. The flow develops both thermally and hydrodynamically while the corrugated-channel walls are kept at a constant temperature. The results indicate a good potential in promoting the thermal performance enhancement by using the nanoparticles under pulsating flow. Because of the flow periodicity, the secondary flow structures occur in the corrugated walls, and improve the mixture between hot and cold fluids. Furthermore, the pulsating flow has the advantage of preventing the sedimentation of nanoparticles in the base fluid. A comparison is presented between the heat transfer coefficients for nanofluids under steady flow conditions and the existing results. The use of nanoparticles under the pulsating flow conditions increases the heat transfer rate compared with the steady flow case. The obtained results are given as a function of dimensionless parameters.]]>

Houda Benlaalam Bouchtout; Amina Mataoui; Faiza Kendil Zidouni

Flow control over a backward-facing step (BFS) by continuous suction/blowing is numerically investigated. This study examines the influence of blowing/suction rate, and slot size on the detachment process. Fluid flow is assumed turbulent, incompressible, 2D and steady in average. The governing equations are discretised by the finite volume method based on the <i>k-ε</i> RNG one point closure turbulence model. The investigations were performed for a Reynolds number of 3.5 10<SUP align="right">4</SUP> with respect to the step height (<i>h</i>). Several blowing/suction rates are checked (-0.035 < <i>C</i><i><SUB align="right"><i>q</i></i> < +0.035) for four slot size cases namely (<i>a</i> = 0.95 mm, 2.25 mm, 3 mm and 5 mm). All results indicate that suction/blowing shortens the reattachment length and reduces the turbulence energy. The detailed flow structure suggests a way of shortening of the recirculation length with increasing the blowing/suction rate. Through different flow conditions, two correlations for reattachment length related to blowing or suction rate are proposed. The smallest slot size produces greatest turbulence kinetic energy and maximum friction all considered suction/blowing rates.]]>

Pankaj K. Gupta

The work reveals an interesting and contra-intuitive observation in numerically simulating the solid-liquid flow field through a straight rotating channel. A previous study (Gupta and Pagalthivarthi, 2007) showed that at moderate rotation rates, increase in rotational speed results in an asymmetric velocity profile, because the Coriolis acceleration tends to increase the level of turbulence on the pressure-side and decrease on the suction-side. The present work contra-intuitively shows that higher rotation rates enhance centrifugal acceleration that pushes the velocity maxima towards the pressure-side of the channel. Centrifugal acceleration is also seen to play a prominent role with increase in inlet concentration. ]]>