A numerical approach for particle-vortex interactions based on volume-averaged equations

To study the dynamics of particles in turbulence when their sizes are comparable to the smallest eddies in the flow, the Kolmogorov length scale, efficient and accurate numerical models for the particle-fluid interaction are still missing. Therefore, we here extend the treatment of the particle feedback on the fluid based on the volume-averaged fluid equations (VA simulation) in the previous study of the present authors, by estimating the fluid force correlated with the disturbed flow. We validate the model against interface-resolved simulations using the immersed-boundary method. Simulations of single particles show that the history effect is well captured by the present estimation method based on the disturbed flow. Similarly, the simulation of the flow around a rotating particle demonstrates that the lift force is also well captured by the proposed method. We also consider the interaction between non-negligible size particles and an array of Taylor-Green vortices. For density ratios $\rho_d/\rho_c\geq$ 10, the results show that the particle motion captured by the VA approach is closer to that of the fully-resolved simulations than that obtained with a traditional two-way coupling simulation. The flow disturbance is also well represented by the VA simulation. In particular, it is found that history effects enhance the curvature of the trajectory in vortices and this enhancement increases with the particle size. Furthermore, the flow field generated by a neighboring particle at distances of around ten particle diameters significantly influences particle trajectories. The computational cost of the VA simulation proposed here is considerably lower than that of the interface-resolved simulation.Comment: 54 pages, 20 figure

Effect of temperature gradient within a solid particle on the rotation and oscillation modes in solid-dispersed two-phase flows

Shintaro Takeuchi, Takaaki Tsutsumi and Takeo Kajishima, "Effect of temperature gradient within a solid particle on the rotation and oscillation modes in solid-dispersed two-phase flows," International Journal of Heat and Fluid Flow, Vol.43, pp.15-25, 2013.動画は論文出版後に追加したものである。 / The video was added after the paper was published

Role of Vortical Structures on the Forced Convective Heat Transfer in Oscillation-Controlled Coaxial-Pipe Heat Exchanger

A numerical simulation of an oscillation-controlled heat-transport coaxial pipe is carried out for studying the flow structure and heat transport characteristics. The heat-transport pipe connects the hot and cold reservoirs, and the cold and hot fluids are discharged with the anti-phase reciprocal waves through circular and annular openings at the ends of the chamber, respectively. By changing the diameter ratio of the circular opening to the inner tube, a unidirectionally circulating flow is observed to develop spontaneously. The flow rate of the unidirectional current is found to be approximately inversely-proportional to the diameter ratio. While the amount of transported heat increases with the flow rate of the unidirectional current (especially when generating strong vortices at the edge of the inner tube) for both cases of thermally-insulated and fully-conductive inner wall, the optimal heat transport performance is attained (not in association with the strongest unidirectional flow) when making zero-averaged vorticity in the cold-end region. For the case of the conductive inner wall, the heat loss across the wall is suppressed with decreasing the diameter ratio, due to the development of the strong jet and radially surrounding shear layer that separate the outer hot fluid from the inner cold fluid.This is a pre-copyedited, author-produced PDF of an article accepted for publication in Journal of Enhanced Heat Transfer following peer review

Large scale analysis of interactive behaviors of bubbles and particles in a liquid by a coupled immersed boundary and vof technique

A new approach for direct numerical simulation of three-phase (gas-liquid-solid) flows is proposed. Implementation of moving rigid surface in a fluid is based on an immersed boundary/solid-object method method developed by the present authors, and gas-liquid interface is captured by volume-of-fluid (VOF) method with an interface reconstruction scheme. The proposed coupling technique enables simulation of flow structures induced by both bubble and particle of comparable sizes, including the flow pattern around the gas-liquid and solid-liquid interfaces. In a suspension of 1024 solid particles and a bubble, some typical behaviours of bubble-particle interaction and liquid flow pattern are captured. The detailed analysis on the motion of the falling particles suggests that the particle rotation is strongly influenced by the behaviours of the rising bubble, giving rise a snap reversal of the rotating directions of the particles due to the flow induced by the bubble.This is a pre-copyedited, author-produced PDF of an article accepted for publication in Multiphase Science and Technology following peer review

Heat transfer and particle behaviours in dispersed two-phase flow with different heat conductivities for liquid and solid

Tsutsumi, T et al. Flow Turbulence Combust (2014) 92: 103. doi:10.1007/s10494-013-9498-0The final publication is available at Springer via http://dx.doi.org/10.1007/s10494-013-9498-0

Heat transfer in natural convection with finite-sized particles considering thermal conductance due to inter­particle contacts

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Computational Thermal Sciences following peer review

A conservative momentum exchange algorithm for interaction problem between fluid and deformable particles

This is the peer reviewed version of the following article:Shintaro Takeuchi, Yoshihiko Yuki, Atsushi Ueyama, Takeo Kajishima, "A conservative momentum exchange algorithm for interaction problem between fluid and deformable particles," International Journal for Numerical Methods in Fluids, Vol.64, Issue 10-12, pp.1084-1101, John Wiley & Sons, 2010, which has been published in final form at http://dx.doi.org/10.1002/fld.2272. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving

A full Eulerian finite difference approach for solving fluid-structure coupling problems

A new simulation method for solving fluid-structure coupling problems has been developed. All the basic equations are numerically solved on a fixed Cartesian grid using a finite difference scheme. A volume-of-fluid formulation (Hirt and Nichols (1981, J. Comput. Phys., 39, 201)), which has been widely used for multiphase flow simulations, is applied to describing the multi-component geometry. The temporal change in the solid deformation is described in the Eulerian frame by updating a left Cauchy-Green deformation tensor, which is used to express constitutive equations for nonlinear Mooney-Rivlin materials. In this paper, various verifications and validations of the present full Eulerian method, which solves the fluid and solid motions on a fixed grid, are demonstrated, and the numerical accuracy involved in the fluid-structure coupling problems is examined.Comment: 38 pages, 27 figures, accepted for publication in J. Comput. Phy

A direct numerical simulation method for complex modulus of particle dispersions

We report an extension of the smoothed profile method (SPM)[Y. Nakayama, K. Kim, and R. Yamamoto, Eur. Phys. J. E {\bf 26}, 361(2008)], a direct numerical simulation method for calculating the complex modulus of the dispersion of particles, in which we introduce a temporally oscillatory external force into the system. The validity of the method was examined by evaluating the storage $G'(\omega)$ and loss $G"(\omega)$ moduli of a system composed of identical spherical particles dispersed in an incompressible Newtonian host fluid at volume fractions of $\Phi=0$, 0.41, and 0.51. The moduli were evaluated at several frequencies of shear flow; the shear flow used here has a zigzag profile, as is consistent with the usual periodic boundary conditions

Boundary induced non linearities at small Reynolds Numbers

We investigate the influence of boundary slip velocity in Newtonian fluids at finite Reynolds numbers. Numerical simulations with Lattice Boltzmann method (LBM) and Finite Differences method (FDM) are performed to quantify the effect of heterogeneous boundary conditions on the integral and local properties of the flow. Non linear effects are induced by the non homogeneity of the boundary condition and change the symmetry properties of the flow inducing an overall mean flow reduction. To explain the observed drag modification, reciprocal relations for stationary ensembles are used, predicting a reduction of the mean flow rate from the creeping flow to be proportional to the fourth power of the friction Reynolds number. Both numerical schemes are then validated within the theoretical predictions and reveal a pronounced numerical efficiency of the LBM with respect to FDM.Comment: 29 pages, 10 figure