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This paper aims to compare the performance of flow pulsation versus flow stirring in the context of mixing of a passive scalar at moderate Reynolds numbers in confined flows. This comparison has been undertaken in two limits: diffusion can be neglected as compared to convection (very large Peclet) and diffusion and convection effects are comparable. The comparison was performed both in terms of global parameters: pumping power and mixing efficiency and local flow topology.

The study has been addressed by setting up a common conceptual three-dimensional problem that consisted of the mixing of two parallel streams in a square section channel past a square section prism. Stirring and pulsation frequencies and amplitudes were changed and combined at an inlet Reynolds number of 200. The numerical model was solved using a finite volume formulation by adapting a series of open-source OpenFOAM computational fluid dynamic (CFD) libraries. For cases with flow pulsation, the icoFoam solver for laminar incompressible transient flows was used. For cases with stirring, the icoDyMFoam solver, which uses the arbitrary Lagrangian–Eulerian method for the description of the moving dynamical mesh, was used to model the prism motion. At the local flow topology level, a new method was proposed to analyze mixing. Time evolution of folding and wrinkling of sheets made up of virtual particles that travel along streak lines was quantified by generating lower rank projections of the sheets onto the spaces spanned by the main eigenvectors of an appropriate space-temporal data decomposition.

In the limit when convection is dominant, the results showed the superior performance of stirring versus flow pulsation both in terms of mixing and required pumping power. In the cases with finite Peclet, the mixing parameters by stirring and flow pulsation were comparable, but pulsation required larger pumping power than stirring. For some precise synchronization of stirring and pulsation, the mixing parameter reached its maximum, although at the expense of higher pumping power. At the local flow topology level, the new method proposed to quantify mixing has been found to correlate well with the global mixing parameter.

A new systematic comparative study of two methods, stirring and pulsation, to achieve mixing of passive scalars in the mini scale for confined flows has been presented. The main value, apart from the conclusions, is that both methods have been tested against the same flow configuration, which allows for a self-consistent comparison. Of particular interest is the fact that it has been found that accurate synchronization of both methods yields mixing parameters higher than those associated to both methods taken separately. This suggests that it is possible to synchronize mixing methods of a different nature to achieve optimum designs. The new theoretical method that has been proposed to understand the mixing performance at the local level has shown promising results, and it is the intention of the authors to test its validity in a broader range of flow parameters. All these findings could be taken as potential guidelines for the design of mixing processes in the mini scale in the process industry.

This paper aims to study the influence that the second invariant of the rate-of-strain tensor of a power law polymeric fluid (aqueous solution of hydroxyethyl cellulose [HEC]) has on convective mixing performance downstream of a 3D confined oscillating prism. Newtonian and non-Newtonian Reynolds numbers, the mass concentration of HEC and prism oscillation frequency were varied.

A conceptual problem was designed. Its objective was to analyze the convective mixing of two adjacent flow streams when they pass around a moving confined prism. The rectangular prism had a square section, and its sinusoidal motion was prescribed inside a channel with a square section too. OpenFOAM libraries were used to simulate the flow field. Regarding prism motion, the icoDyMFoam solver was used. The problem was analyzed both at the global level (mixing parameter) and local level (detailed flow topology).

For constant Reynolds number, increasing mass concentrations of HEC (in the range from 0.2% to 0.5%) led to better mixing parameters. The improvement was linked to the effect that the second invariant of the rate-of-strain tensor had on flow topology. It was found that mixing is maximum when the prism motion and its wake (the frequency of the first instability) are synchronized. In practical terms, this means that the optimum stirring frequency does not need to be very high; it suffices that it ensures that synchronization occurs. The dominant vorticity shedding pattern found was the so-called 2P mode. However, a significant difference was found when compared to the free-stream situation. While in the former, the two vorticity regions that make up the 2P pair come from the prism, in the present confined case, one came from the prism, and the other came from the wall. Another difference was that in the present case, the 2P pairs were much more elongated than in the free stream case, and this had a significant influence on the stretching and bending of streak lines and, therefore, on mixing.

The study that has been presented has a practical industrial implication for the processes industry because it provides guidelines to design active mixers that deal with aqueous power law polymeric solutions. In parallel, it opens up some new research lines in the direction of studying whether the mixing concept might be modified so as to develop a fully passive system that could be far simpler and, possibly, more attractive to industry.

The originality and value of the study are associated to the systematic approach that has been followed. It has allowed to establish a clear pattern regarding the active mixing behavior of HEC solutions in confined flows. To the best of authors’ knowledge, this could be the first study of this type in the literature. Also, the study has contributed to understand the vorticity shedding patterns that appear in these types of problems and how they shape wake topology and, consequently, mixing performance. The finding that optimum mixing requires synchronization of stirring motion frequency and wake first natural frequency of instability may help to improve the design and operation of industrial mixers dealing with polymeric aqueous solutions.

Friction stir welding (FSW) butt-joining involving the use of a dissimilar filler metal insert between the retreating and advancing portions of the workpiece is investigated computationally using a combined Eulerian-Lagrangian (CEL) finite element analysis (FEA). The emphasis of the computational analysis was placed on the understanding of the inter-material mixing and weld-flaw formation during a dissimilar-material FSW process. The paper aims to discuss these issues.

The FEA employed is of a two-way thermo-mechanical character (i.e. frictional-sliding/plastic-work dissipation was taken to act as a heat source in the energy conservation equation), while temperature is allowed to affect mechanical aspects of the model through temperature-dependent material properties. Within the analysis, the workpiece and the filler-metal insert are treated as different materials within the Eulerian subdomain, while the tool was treated as a conventional Lagrangian subdomain. The use of the CEL formulation within the workpiece insert helped avoid numerical difficulties associated with excessive Lagrangian element distortion.

The results obtained revealed that, in order to obtain flaw-free FSW joints with properly mixed filler and base materials, process parameters including the location of the tool relative to the centerline of the weld must be selected judiciously.

To the authors’ knowledge, the present work is the first reported attempt to simulate FSW of dissimilar materials.

The purpose of this paper is to describe how electromagnetic stirring during continuous casting of ferrous and non‐ferrous metals is applied in order to increase the homogeneity and the material properties by improving the grain refinement in the solidification process. The fluid flow and thermal modeling was performed for studying the metal wire pulling process, where melt is being stirred at the solidification front (SF) by electromagnetic forces. Transient simulation has been carried out in order to investigate the periodical character of the process.

The numerical analysis was performed in 2D utilizing the rotational symmetry of the problem. First the electromagnetic fields were estimated using FEM and were subsequently exported as source terms in a coupled thermal and flow simulation with FVM.

The presented numerical model estimated the most suitable position between the stirring coil and the SF to achieve high flow velocities which improve the grain refinement process.

This work enables estimation of the melt solidification in an electromagnetic stirred continuous casting process with oscillating pull velocities.

To produce a controlled stirring in a low conducting liquid thanks to a new kind of multiphase inductor.

An experimental pilot consisting of a cylindrical salt water pool surrounded by an innovative multiphase inductor configuration, based on the single phase asynchronous motor principle, is setup. The maximum bulk stirring velocities are measured and compared with the estimate by numerical modelling.

Shows the possibility of controlling the stirring of a low conducting liquid thanks to a multiphase inductive system. The corresponding measurement results give a significant bulk velocity of a few centimetres per second.

This new kind of multiphase inductor, working with a single phase induction generator, seems a promising way to produce a controlled stirring in low conducting media which cover a large range of induction applications.

Such an innovative inductor configuration has already been tested successfully for metal alloys stirring in the middle frequency area. In this paper, an extension of this kind of multiphase inductive system for electromagnetic stirring of low conducting liquids like electrolytes in the high frequency area is presented.

Stir casting is a promising technique used for the manufacture of Al-SiC metal matrix composites. The clustering of reinforcement particles is a serious concern in this production method. In this work, mushy-state solidification characteristics in stir casting are numerically simulated using computational fluid dynamics techniques to study the clustering of reinforcement particles.

Effects of process parameters on the distribution of particles are examined by varying stirrer speed, volume fraction of reinforcement, number of blades on stirrer and diameter ratio (ratio of crucible diameter to stirrer diameter). Further, investigation of characteristics of cooling curves during solidification process is carried out. Volume of fluid method in conjunction with a solidification model is used to simulate the multi-phase fluid flow during the mushy-state solidification. Solidification patterns thus obtained clearly indicate a strong influence of process parameters on the distribution of reinforcement particles and solidification time.

From the simulation study, it is observed that increase in stirrer speed from 50 to 150 rad/s promotes faster solidification rate. But, beyond 100 rad/s, stirrer speed limit, clustering of reinforcement particles is observed. The clustering of reinforcement particles is seen when volume fraction of reinforcement is increased beyond 10 per cent. When number of blades on stirrer are increased from three to five, an increase in solidification rate is observed, and an uneven distribution of reinforcement particles are observed for five-blade geometry. It is also seen from the simulation study that a four-blade stirrer gives a better distribution of reinforcement in the molten metal. Decrease in diameter ratio from 2.5 to 1.5 promotes faster solidification rate.

There is 90 per cent closeness in results for simulation study and the published experimental results.

The purpose of this study is to develop a novel rectangular linear induction motor as an electromagnetic stirrer (EMS) using analytical followed by a numerical approach. The rectangular linear electromagnetic stirrer (RLEMS) is mainly developed for rectangular slab and billet as the end product.

A two-dimensional analytical approach for evaluating flux density distribution within the mold is established for RLEMS structure. Subsequently, the average stirring force within the mold is estimated from those field variables. The paper presents an analytical and numerical model for calculating the stirring force and counters the end and edge effects of linear-type EMS. Magnetic field and force profile within the mold due to polyphase rectangular stator distribution has been done with the help of Maxwell’s equation with appropriate boundary conditions by using Fourier transform and inverse Fourier transform. Subsequently, a numerical study has been carried out using a coupled thermal and electromagnetic model.

The present study investigates the physical phenomena during the solidification process because of an induced electromagnetic field and is able to extract all the electromagnetic field variables under different operating conditions, and, subsequently, provides an insight into the actual happening within the mold.

It provides the analytical method for solving the stirring force of the proposed new RLEMS structure by addressing the smooth and efficient variation of field and velocity profile near the corner of the mold and improves the quality of end product.

The friction stir welding (FSW) process comprises several highly coupled (and non‐linear) physical phenomena: large plastic deformation, material flow transportation, mechanical stirring of the tool, tool‐workpiece surface interaction, dynamic structural evolution, heat generation from friction and plastic deformation. This paper aims to present an advanced finite element (FE) model encapsulating this complex behaviour and various aspects associated with the FE model such as contact modelling, material model and meshing techniques are to be discussed in detail.

The numerical model is continuum solid mechanics‐based, fully thermo‐mechanically coupled and has successfully simulated the FSW process including plunging, dwelling and welding stages.

The development of several field variables are quantified by the model: temperature, stress, strain. Material movement is visualized by defining tracer particles at the locations of interest. The numerically computed material flow patterns are in very good agreement with the general findings from experiments.

The model is, to the best of the authors' knowledge, the most advanced simulation of FSW published in the literature.

The numerical simulation of two‐dimensional incompressible complex flows of viscoelastic fluids is presented. The context is one, relevant to the food industry (dough kneading), of stirring within a cylindrical vessel, where stirrers are attached to the lid of the vessel. The motion is driven by the rotation of the outer vessel wall, with various stirrer locations. With a single stirrer, both a concentric and an eccentric configuration are considered. A double‐stirrer eccentric case, with two symmetrically arranged stirrers, is also contrasted against the above. A parallel numerical method is adopted, based on a finite element semi‐implicit time‐stepping Taylor‐Galerkin/pressure‐correction scheme. For viscoelastic fluids, constant viscosity Oldroyd‐B and two shear‐thinning Phan‐Thien/Tanner constitutive models are employed. Both linear and exponential models at two different material parameters are considered. This permits a comparison of various stress, shear and extensional properties and their respective influences upon the flow fields generated. Variation with increasing speed of vessel and change in mixer geometry are analysed with respect to the flow kinematics and stress fields produced. Optimal kneading scenarios are commended with asymmetrical stirrer positioning, one‐stirrer proving better than two. Then, models with enhanced strain‐hardening, amplify levels of localised maxima in rate‐of‐work done per unit power consumed. Simulations are conducted via distributed parallel processing, performed on work‐station clusters, employing a conventional message passing protocol (PVM). Parallel results are compared against those obtained on a single processor (sequential computation). Ideal linear speed‐up with the number of processors has been observed.

Friction stir processing (FSP) is overviewed with the process variables, along with the thermal aspect of different metals.

With its inbuilt advantages, FSP is used to reduce the failure in the structural integrity of the body panels of automobiles, airplanes and lashing rails. FSP has excellent process ability and surface treatability with good corrosion resistance and high strength at elevated temperatures. Process parameters such as rotation speed of the tool, traverse speed, tool tilt angle, groove design, volume fraction and increase in number of tool passes should be considered for generating a processed and defect-free surface of the workpiece.

FSP process is used for modifying the surface by reinforcement of composites to improve the mechanical properties and results in the ultrafine grain refinement of microstructure. FSP uses the frictional heat and mechanical deformation for achieving the maximum performance using the low-cost tool; the production time is also very less.

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