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The purpose of this study is to examine the physical processes experienced by a particle-laden gas due to various types of collisions, different heat transfer modalities and jet axis switching. Here, attention is focused on a particle-laden gas subjected to jet axis switching while experiencing fluid flow and heat transfer.

The methodology used to model and solve these complex problems is numerical simulation treated here as a two-phase turbulent flow in which the gas and the particles keep their separate identities. For the turbulent flow model, validation was achieved by comparisons with appropriate experimental data. The considered interactions between the fluid and the particles include one-way fluid–particle interactions, two-way fluid–particle interactions and particle–particle interactions.

For the fluid flow portion of the work, emphasis was placed on the particle collection efficiency and on independent variables that affect this quantity and the trajectories of the fluid and of the particles as they traverse the space between the jet orifice and the impingement plate. The extent of the effect depended on four factors: particle size, particle density, number of particles and the velocity of the fluid flow. The major effect on the heat transferred to the impingement plate occurred when direct heat transfer between the impinging particles and the plate was taken into account.

This paper deals with issues never before dealt with in the published literature: the effect of jet axis switching on the fluid mechanics of gas-particle flows without heat transfer and the effect of jet axis switching and the presence of particles on jet impingement heat transfer. The overall focus of the work is on the impact of jet axis switching on particle-laden fluid flow and heat transfer.

This study aims to modify the standard probabilistic lattice Boltzmann methodology (LBM) cellular automata (CA) algorithm to enable a more realistic and accurate computation of the ensemble rather than individual particle trajectories that need to be updated from one time step to the next (allowing, as such, a fraction of the collection of particles in any lattice grid cell to be updated in a time step, rather than the entire collection of particles as in the standard LBM-CA algorithm leading to a better representation of the dynamic interaction between the particles and the background flow). Exploitation of the inherent parallelism of the modified LBM-CA algorithm to provide a computationally efficient scheme for computation of particle-laden flows on readily available commodity general-purpose graphics processing units (GPGPUs).

This paper presents a framework for the implementation of a LBM for the simulation of particle transport and deposition in complex flows on a GPGPU. Towards this objective, the authors have shown how to map the data structure of the LBM with a multiple-relaxation-time (MRT) collision operator and the Smagorinsky subgrid-scale turbulence model (for turbulent fluid flow simulations) coupled with a CA probabilistic method (for particle transport and deposition simulations) to a GPGPU to give a high-performance computing tool for the calculation of particle-laden flows.

A fluid-particle simulation using our LBM-MRT-CA algorithm run on a single GPGPU was 160 times as computationally efficient as the same algorithm run on a single CPU.

The method is limited by the available computational resources (e.g. GPU memory size).

A new 3D LBM-MRT-CA model was developed to simulate the particle transport and deposition in complex laminar and turbulent flows with different hydrodynamic characteristics (e.g. vortex shedding, impingement, free shear layer, turbulent boundary layer). The solid particle information is encapsulated locally at the lattice grid nodes, allowing for straightforward mapping of the datastructure onto a GPGPU enabling a massive parallel execution of the LBM-MRT-CA algorithm. The new particle transport algorithm was based on the local (bulk) particle density and velocity and provides more realistic results for the particle transport and deposition than the standard LBM-CA algorithm.

The purpose of this paper is to develop a corrected unresolved CFD-DEM method that can reproduce the wake effects in modeling particulate flows at moderate Reynolds number.

First, the velocity field in the wake behind a settling particle is numerically investigated by a resolved method, in which the finite volume method (FVM) is applied to model the fluid flow, discrete element method (DEM) is applied to simulate the motion of particles and immersed boundary method (IBM) is used to tackle fluid solid interaction. Second, an analytical scaling law is given, which can effectively describe the velocity field in the wake behind the settling particle at low and middle Reynolds numbers. Third, this analytical expression is incorporated into unresolved modeling to correct the relative velocity between the particle and its surrounding fluid and enable the influence of the wake of the particle on its neighboring particles.

Two numerical examples, the sedimentation of dual particles, a list of particles and even more particles are provided to show the effectiveness of the presented velocity corrected unresolved method (VCUM). It is found that, in both examples simulated with VCUM, the relative positions of the particles changed, and drafting & kissing phenomenon and particle clustering phenomenon were clearly observed.

The developed VCUM can be highly beneficial for modeling industrial particulate flows with DKT and particle clustering phenomena.

VCUM innovatively incorporates the wake effects into unresolved CFD-DEM method. It improves the computational accuracy of conventional unresolved methods with comparable results from resolved modeling, while the computational cost is greatly reduced.

Experiments to investigate the characteristic distribution of nanoparticle-laden gas flow around a circular cylinder were performed with a fast mobility particle spectrometer. The paper aims to discuss these issues.

The fast mobility particle sizer spectrometer is used to measure quasi-instantaneous particle number density. The acquired particle number density, total concentration, and geometric mean diameter at free stream and in the wake were used to discuss the particle characteristic distribution. The time-averaged velocity field detected by particle imaging velocimetry was used to investigate the effect of carried phase on nanoparticles distribution.

Results show that the total particle concentration in the free stream is larger than that in the wake. However, the geometric mean diameter of particle in the free stream is smaller than that in the wake for different Re. The total particle concentration and geometric mean diameter in the free stream and the wake both change in the same way, but with an obvious lag which increases with Re. Despite particle deposition, the number density of particles with electrical-mobility-equivalent diameters in the range from 220.7 to 523.3 nm in the wake is still higher than that in the free stream.

Though the particles-laden gas flow around a circular cylinder had been studied experimentally and numerically before, where particles are larger than one micrometer, investigators paid little attention on the nanoparticles-laden gas flow where particles are smaller than one micrometer, especially at high Reynolds number, because numerical methods so far cannot deal these problems completely and satisfactorily. However, this issue is widely existing in nature and engineering application, such as superfine dust or microorganism captured by a circular cylinder model.

Numerical results are reported for a dilute turbulent liquid‐solid flow in an axisymmetric sudden‐expansion pipe with an expansion ratio 2:1. The two‐phase flow has a mass‐loading ratio low enough for particle collision to be negligible. The numerical predictions for the dilute two‐phase flow are based on a hybrid Eulerian‐Lagrangian model. A nonlinear k‐ε model is used for the fluid flow to account for the turbulence anisotropy and an improved eddy‐interaction model is used for the particulate flow to account for the effects of turbulence anisotropy, turbulence inhomogeneity, particle drift, and particle inertia on particle dispersion. The effects of the coupling sources, the added mass, the lift force and the shear stress on two‐phase flow predictions are separately studied. The numerical predictions obtained with the improved and conventional particle dispersion models are compared with experimental measurements for the mean and fluctuating velocities at the different measured planes.

The purpose of this paper is to study nanoparticles diffusion and coagulation processes in a twin-jet.

Large eddy simulation (LES) and Taylor-series expansion moment method (TEMOM) are employed to deal with a nanoparticle-laden twin-jet flow.

The numerical results show that the interaction of the two jets and turbulence eddy structures rolling-up, paring and shedding in flow sharply affects particles number concentration. Particle diameter grows quickly at the interfaces of jets. Coagulation shows more obvious effect at initial stage than that in the subsequent period. Then diffusion makes the particle diameter distribution much more uniform.

In recent years a great number of attentions have been focussed on the issue of particulate dynamics processes including diffusion, coagulation and deposition, etc. However, up to now few works have been focus on the nanoparticles coagulation and dispersion in turbulent flows. The investigation on the diffusion and coagulation process of nanoparticles using TEMOM in a twin-jet flow has not been found.

This paper aims to derive a reduced-order model for the heat transfer across the interface between a millimetric thermocapillary liquid bridge from silicone oil and the surrounding ambient gas.

Numerical solutions for the two-fluid model are computed covering a wide parametric space, making a total of 2,800 numerical flow simulations. Based on the computed data, a reduced single-fluid model for the liquid phase is devised, in which the heat transfer between the liquid and the gas is modeled by Newton’s heat transfer law, albeit with a space-dependent Biot function Bi(z), instead of a constant Biot number Bi.

An explicit robust fit of Bi(z) is obtained covering the whole range of parameters considered. The single-fluid model together with the Biot function derived yields very accurate results at much lesser computational cost than the corresponding two-phase fully-coupled simulation required for the two-fluid model.

Using this novel Biot function approach instead of a constant Biot number, the critical Reynolds number can be predicted much more accurately within single-phase linear stability solvers.

The Biot function for thermocapillary liquid bridges is derived from the full multiphase problem by a robust multi-stage fit procedure. The derived Biot function reproduces very well the theoretical boundary layer scalings.

The aims of this study were to investigate the effect of using a wall‐normal, 2D micro zero‐net‐mass‐flux (ZNMF) jet located at the leading edge of a NACA 0015 airfoil to actively control flow separation and enhance lift.

Experiments were conducted over a two‐dimensional airfoil in a water tunnel at a Reynolds number of 3.08 × 10⁴ for the parametric investigation and the detailed multigrid cross‐correlation digital particle image velocimetry (MCCDPIV) measurements. Flow visualisation experiments were carried out at a lower Reynolds number of 1.54 × 10⁴.

The largest lift increase was observed when a non‐dimensional frequency of 1.3 and an oscillatory momentum blowing coefficient of 0.14 per cent was employed. Under these forcing conditions the stall angle of the airfoil was mitigated from an angle of attack of 10^o to one of 18^o, resulting in a maximum lift coefficient increase of 46 per cent above the uncontrolled lift coefficient. Planar laser induced fluoroscopy and MCCDPIV revealed that the lift increments were the result of the generation of a train of large‐scale, spanwise lifting vortices that convected over the suction surface of the airfoil. The presence of these structures resulted in the flow seemingly remaining attached to the upper surface of the airfoil for a wider range of angles of attack.

This study is significant as it provides quantitative experimental data, which clearly demonstrates the effectiveness of a 2D micro ZNMF jet in controlling flow separation of a NACA 0015 airfoil at high angles of attack and thus, enhancing lift. Furthermore, the flow visualisations and MCCDPIV measurements have provided insight into the mechanisms responsible for the improvement in lift. This new understanding has applications beyond the NACA 0015 airfoil used in this study.

The purpose of this paper is to present two different methods for the imposition of thermal boundary conditions (BCs) in the framework of two-phase flows: an immersed boundary method (IBM) and a Ghost cell method. Both methods are able to handle Dirichlet as well as Neumann BCs.

Direct numerical simulations of two-phase flows are performed where the thermal BCs at the phase boundary is accounted for with two different approaches.

Both methods are validated with the results obtained on a body-fitted mesh. Simulations of the three-dimensional flow and temperature field around a sphere demonstrate versatility and accuracy of both methods.

This is the first time Neumann BCs are imposed by means of an IBM with a direct heating approach employing regularized delta functions. The test cases considered may also serve as benchmarks for other studies.

In the process of conveying the solid–liquid two-phase medium of the centrifugal slurry pump, the wear of the flow-passing parts is an important problem affecting its life and safe operation. Therefore, a numerical investigation on the wear characteristics of the centrifugal slurry pump under different particle conditions was conducted.

A solid-liquid two-phase model based on CFD-DEM coupling is established and used to analyze the flow field and the wear characteristics of the flow-passing parts with different particle densities, volume fractions and sizes.

Particle conditions will affect the pump flow field. To analyze the pump wear characteristics, the wear distribution, wear value and cumulative force laws of flow-passing parts under different particle conditions are obtained. In each flow-passing part, with the increase of particle density, volume fraction and size, the wear area is concentrated and the wear depth increases. Under different particle conditions, the wear is mainly on the volute chamber and the blade pressure surface, and the tangential cumulative force of flow-passing parts is much larger than the normal cumulative force.

An accurate model and a coupled simulation method for predicting the wear of the slurry pump are obtained, and the wear characteristic law can provide a reference for the design of the slurry pump to reduce friction.