Fluid Coupling Research Articles

Impact damage assessment in biocomposites by micro-CT and innovative air-coupled detection of laser-generated ultrasound

The increasing use of natural fibre composites in at least semi-structural applications along with a demand for a fast and accurate damage detection for quality purpose and in-service reliability promote a need for non-contact non-destructive testing techniques. To this purpose, ultrasound is probably one of the most widely used testing techniques but the need of a coupling fluid like water limits its use with natural fibre composites. In this work, a novel non-contact set-up based on laser excitation of ultrasound and detection with a broadband, air-coupled optical microphone is presented and tested on flax/PLA laminates. This material system has been characterized in terms of quasi-static mechanical properties and low velocity impact response. The outcomes of this study demonstrate the potential of this non-contact and nondestructive system for quality and damage inspection purposes of natural fibre composites.

Partitioned simulation of multi‐field problems – efficient and robust coupling of fluids and structures

AbstractStrongly coupled multifield problems arise in various engineering applications. Fluid‐structure interaction problems are one of the most prominent examples, especially in maritime applications. Choosing a partitioned solution approach allows to reuse existing software that was specialized to solve the underlying structural and fluid dynamics subproblems. In this work, the general partitioned solution approach is applied to investigate the hydrodynamics around an elastic marine‐propeller. The software library comana is used to steer the solution process. It allows to couple a boundary element solver for the fluid subproblem with a finite element solver for the structural subproblem. It is shown that novel convergence acceleration methods ensure a stable and efficient simulation for different coupling algorithms.

Modified mathematical model for variable fill fluid coupling

Variable fill fluid couplings are used in the speed control units. Also, variation in coupling oil volume is used in adapting one size of coupling to a wider range of power transmission applications. Available model for the partially filled fluid couplings, has a good performance for couplings with fixed amount of oil but their performance will be degraded if they are used for the variable fill couplings. In this paper, the current model for partially filled fluid couplings is modified to have better performance for variable fill couplings. For this purpose, the circulation loss calculation is modified and also, the effect of oil temperature variations and blade thickness are included in the model. The effect of these modification on the model performance are investigated in couple of simulations. Comparing the simulation results with the available experimental data shows that the suggested modifications can improve the model performance very well.

Magnetocapacitance and magnetoelectric coupling effect of Ni0.5Cu0.5Fe2O4/BaTiO3 mixed multiferroic fluids

Ni0.5Cu0.5Fe2O4/BaTiO3 (NCFO/BTO) mixed multiferroic fluids were prepared by distributing surfactant treated NCFO and BTO particles in to a highly-insulating base fluid, the magnetocapacitance and magnetoelectric coupling effect were investigated. The results indicate that the sample shows strong magnetoelectric coupling effect, in which both the coercive field Ec and remanent polarization Pr enhance obviously under the action of magnetic field, while the dielectric constant decreases with increasing the magnetic field, revealing negative magnetocapacitance phenomenon. Large direct magnetolectric coupling coefficient was estimated to be α ∼ 76 V/(cm−1.Oe), which is several orders of magnitude larger than that of conventional magnetoelectric composite ceramics. Further analysis indicates that the possibility of movement, aggregation and chain-like structure of the particles in the presence of external field is believed to be responsible for the observed negative magnetocapacitance and strong magnetoelectric coupling effect. The results show that the strong room temperature magnetoelectric effect of the mixed magnetoelectric fluids is the product of the deformation of the particle distribution and the utilization of clamping force under external field. This magnetoelectric coupling effect is different from that of conventional composite materials which is directly coupled via the interface interaction, which will be advantageous for practical applications.

The photothermoelectric effect of liquid thermoelectrics as a tool for the detection of ferro–paraelectric phase transitions in solids

A new application of the liquid thermoelectrics (LTE) is proposed: the detection of phase transitions in ferroelectric solids. Concretely, the Seebeck effect generated in a known LTE material (dodecanol + 10−1 mol L−1 tetrabutylammonium nitrate) was used as a tool for the detection of the antiferro–paraelectric phase transition of triglycine sulphate (TGS). TGS was selected as a sample because it is a ferroelectric solid with a convenient Curie point close to room temperature (about 49 °C). The advantages of the present method (compared with previously reported investigations performed with solid thermoelectric materials as sensors) are two: (1) no coupling fluid between the sensor and sample is necessary (the liquid sensor–solid sample thermal contact is perfect); (2) the liquid sensor allows for investigations of samples with irregular geometry. Based on the recently developed theory of the photothermoelectric method, the behaviour of the static volume specific heat and dynamic thermal diffusivity, conductivity and effusivity of TGS around the Curie point has been obtained.

Modeling sterilization value and nutrient degradation in the thermal processing of liquid foods under diffusive laminar flow with associations of tubular heat exchangers

AbstractThermal processing of a liquid food under diffusive laminar flow was modeled coupling fluid flow, heat transfer, diffusion, and inactivation/degradation kinetics. Model considers associated countercurrent tubular exchangers for heating and cooling and the holding tube. Axial and radial distributions of temperature and concentration in the food product (non‐Newtonian power‐law flow) were accounted and parameters for effective diffusion of heat and mass were used to model enhanced transfer from corrugate tubes or coils. Heat exchanged with environment was included. A case study of 40.2 °Brix blackberry juice pasteurization is presented, and results discussed. Influence of effective diffusivities, inlet heating media temperature and product flow rate were analyzed, and it was possible to minimize anthocyanin degradation while meeting food safety requirements (5‐log reduction on yeasts) considering the contributions from the whole process.Practical applicationsMathematical modeling of a chemical process based on first principles, also called physical or phenomenological models, is a powerful tool to couple fluid flow, heat transfer, mass diffusion, and reaction kinetics, thus creating a virtual prototype of the process that is useful for design, analysis, control, and optimization. The model presented considers important features that are often neglected in process design, but without unnecessarily increasing complexity and computational requirements, such as in a CFD model (computational fluid dynamics) that requires a detailed representation of the geometry and specialized software and hardware for simulation. Lower computational times allow the use of this model to solve optimization or predictive control problems with a reliable representation of transport phenomena and reaction kinetics.

Numerical study of Low Salinity Water Alternating CO2 injection for enhancing oil recovery in a sandstone reservoir: Coupled geochemical and fluid flow modeling

The combination of low salinity water with gas in the form of water alternating CO2 injection (CO2-LSWAG) is a promising EOR method that could simultaneously benefit from gas mobility control and also rock wettability alteration to more water-wet as consequence of geochemical interaction between rock and reservoir fluids. This paper aims to investigate the EOR potential of CO2-LSWAG under miscible conditions in a sandstone oil reservoir by coupling fluid flow and geochemical modeling. The wettability alteration of the rock surface was described by a series of relevant geochemical reactions between rock and low salinity water in a compositional simulator. The concept of ion equivalent fraction was used as the wettability index during CO2-LSWAG injection. It consists mainly of the effects of ion exchange and clay properties on oil-water relative permeability functions. Also, the effect of calcite mineral dissolution was studied as result of interaction with low salinity water and CO2 gas using relevant geochemical reactions. Results showed that salinity difference between injected and formation water triggers ion exchange processes between water and rock. Also, the rate of calcite dissolution increased due to the CO2 partitioning into the aqueous phase. The calcite dissolution caused the increase of calcium ions in the reservoir leading to more water-wet condition. However, results indicated that the rate of calcite dissolution decreased far from the injection well most likely due to reduced interaction time between low salinity water with dissolved CO2 and the reservoir rock. The oil recovery results showed that CO2-LSWAG is capable of producing incremental oil as much as 10% of the initial oil in place on top of high salinity CO2-WAG. The results of this numerical study support the potential application of CO2-LSWAG as an efficient EOR method in sandstone reservoirs.

Simple analytic model for optimally sizing thermoelectric generator module arrays for waste heat recovery

Thermoelectric generators (TEGs) are commonly used in waste heat recovery (WHR) applications. Counter-intuitively, recent studies have demonstrated that there is an optimal number of TEG modules to use in a WHR system for maximum power output. General rules for identifying this limit have not yet been proposed. In this study, a simple analytic model is derived to describe WHR systems, and predict the optimal TEG module array size. This model incorporates a new thermal-fluid figure of merit (HT), which accounts for coupled effects of TEG module thermal conductance, heat exchanger performances, and coupling fluid stream thermal capacity rates. The model is experimentally validated with data from a small-scale test facility. The model is used to predict performance trends of (1) TEG arrays with varying module counts at low and high fluid thermal capacity rates, (2) TEG arrays with fixed overall heat exchanger conductances (UAs) and UAs proportional to module-count, and (3) multi-row TEG arrays. Guidelines for selecting optimal numbers of TEG modules are recommended for these cases. The application of this model is illustrated through analysis of a vehicle WHR system. This analytic model can guide preliminary WHR system designs, which can be refined with sophisticated computational and experimental approaches.

Dissipative Coupling of Fluid and Immersed Objects for Modelling of Cells in Flow.

Modelling of cell flow for biomedical applications relies in many cases on the correct description of fluid-structure interaction between the cell membrane and the surrounding fluid. We analyse the coupling of the lattice-Boltzmann method for the fluid and the spring network model for the cells. We investigate the bare friction parameter of fluid-structure interaction that is mediated via dissipative coupling. Such coupling mimics the no-slip boundary condition at the interface between the fluid and object. It is an alternative method to the immersed boundary method. Here, the fluid-structure coupling is provided by forces penalising local differences between velocities of the object's boundaries and the surrounding fluid. The method includes a phenomenological friction coefficient that determines the strength of the coupling. This work aims at determination of proper values of such friction coefficient. We derive an explicit formula for computation of this coefficient depending on the mesh density assuming a reference friction is known. We validate this formula on spherical and ellipsoidal objects. We also provide sensitivity analysis of the formula on all parameters entering the model. We conclude that such formula may be used also for objects with irregular shapes provided that the triangular mesh covering the object's surface is in some sense uniform. Our findings are justified by two computational experiments where we simulate motion of a red blood cell in a capillary and in a shear flow. Both experiments confirm our results presented in this work.

Stochastic dynamics of fluid–structure interaction in turbulent thermal convection

The motion of a free-moving plate atop turbulent thermal convection exhibits diverse dynamics that displays characteristics of both deterministic and chaotic motions. Early experiments performed by Zhong & Zhang (Phys. Rev. E, vol. 75 (5), 2007, 055301) found an oscillatory and a trapped state existing for a plate floating on convective fluid in a rectangular tank. They proposed a piecewise smooth physical model (ZZ model) that successfully captures this transition of states. However, their model was deterministic and therefore could not describe the stochastic behaviours. In this study, we combine the ZZ model with a novel approach that models the stochastic aspects through a variational inequality structure. With the powerful mathematical tools for stochastic variational inequalities, the properties of the Markov process and corresponding Kolmogorov equations could be studied both numerically and analytically. Moreover, this framework also allows one to compute the transition probabilities. Our present work captures the stochastic aspects of the two aforementioned boundary–fluid coupling states, predicts the stochastic behaviours and shows excellent qualitative and quantitative agreements with the experimental data.

A unified Lagrangian formulation for solid and fluid dynamics and its possibility for modelling submarine landslides and their consequences

Consequences of submarine landslides include both their direct impact on offshore infrastructure, such as subsea electric cables and gas/oil pipelines, and their indirect impact via the generated tsunami. The simulation of submarine landslides and their consequences has been a long-standing challenge majorly due to the strong coupling among sliding sediments, seawater and infrastructure as well as the induced extreme material deformation during the complete process. In this paper, we propose a unified finite element formulation for solid and fluid dynamics based on a generalised Hellinger–Reissner variational principle so that the coupling of fluid and solid can be achieved naturally in a monolithic fashion. In order to tackle extreme deformation problems, the resulting formulation is implemented within the framework of the particle finite element method. The correctness and robustness of the proposed unified formulation for single-phase problems (e.g. fluid dynamics problems involving Newtonian/Non-Newtonian flows and solid dynamics problems) as well as for multi-phase problems (e.g. two-phase flows) are verified against benchmarks. Comparisons are carried out against numerical and analytical solutions or experimental data that are available in the literature. Last but not least, the possibility of the proposed approach for modelling submarine landslides and their consequences is demonstrated via a numerical experiment of an underwater slope stability problem. It is shown that the failure and post-failure processes of the underwater slope can be predicted in a single simulation with its direct threat to a nearby pipeline and indirect threat by generating tsunami being estimated as well.

Simulation of Fluid-Thermal Field in Oil-Immersed Transformer Winding Based on Dimensionless Least-Squares and Upwind Finite Element Method

In order to study the coupling fluid and thermal problems of the local winding in oil-immersed power transformers, the least-squares finite element method (LSFEM) and upwind finite element method (UFEM) are adopted, respectively, to calculate the fluid and thermal field in the oil duct. When solving the coupling problem by sequential iterations, the effect of temperature on the material property and the loss density of the windings should be taken into account. In order to improve the computation efficiency for the coupling fields, an algorithm, which adopts two techniques, the dimensionless LSFEM and the combination of Jacobi preconditioned conjugate gradient method (JPCGM) and the two-side equilibration method (TSEM), is proposed in this paper. To validate the efficiency of the proposed algorithm, a local winding model of a transformer is built and the fluid field is computed by the conventional LSFEM, dimensionless LSFEM, and the Fluent software. While the fluid and thermal computation results of the local winding model of a transformer obtained by the two LSFEMs are basically consistent with those of the Fluent software, the stiffness matrix, which is formed by the dimensionless scheme of LSFEM and preconditioned by the JPCGM and TSEM, has a smaller condition number and a faster convergence rate of the equations. Thus, it demonstrates a broader applicability.

Thermophysical Parameters Evaluation by Pyroelectric Detection

The different configurations of the photopyroelectric calorimetry which can be adopted for the evaluations of the thermophysical parameters in liquids and in solids, and the advantages, with respect to other calorimetric techniques, are briefly described. A review of the recent results obtained by the photopyroelectric back-detection configuration for the determination of the different thermophysical properties in various materials is presented with particular attention to the cases where the temperature dependence of such parameters is studied. The results concerning the studies carried out by performing simultaneous calorimetric and imaging evaluations are also described. Finally, the possibility of performing “absolute” measurements of the thermal parameters, eliminating the influence of eventual coupling fluid, is discussed.

Determination of mechanical properties of biofilms by modelling the deformation measured using optical coherence tomography

The advantage of using non-invasive imaging such as optical coherence tomography (OCT) to asses material properties from deformed biofilm geometries can be compromised by the assumptions made on fluid forces acting on the biofilm. This study developed a method for the determination of elastic properties of biofilms by modelling the biofilm deformation recorded by OCT imaging with poroelastic fluid-structure interaction computations. Two-dimensional biofilm geometries were extracted from OCT scans of non-deformed and deformed structures as a result of hydrodynamic loading. The biofilm geometries were implemented in a model coupling fluid dynamics with elastic solid mechanics and Darcy flow in the biofilm. The simulation results were compared with real deformed geometries and a fitting procedure allowed estimation of the Young's modulus in given flow conditions. The present method considerably improves the estimation of elastic moduli of biofilms grown in mini-fluidic rectangular channels. This superior prediction is based on the relaxation of several simplifying assumptions made in past studies: shear stress is not anymore taken constant over the biofilm surface, total stress including also pressure is accounted for, any biofilm shape can be used in the determinations, and non-linear behavior of mechanical properties can be estimated. Biofilm elastic moduli between 70 and 700 Pa were obtained and biofilm hardening at large applied stress due to increasing flow velocity was quantified. The work performed here opens the way for in-situ determination of other mechanical properties (e.g., viscoelastic properties, relaxation times, plastic yields) and provides data for modelling biofilm deformation and detachment with eventual applications in biofilm control and removal strategies.

Evolution of the As‐Cast Grain Microstructure of an Ultrasonically Treated Al–2Cu Alloy

The evolution of the grain structure of an Al–2Cu alloy is investigated numerically during its solidification while being subjected to ultrasonic treatment. A CAFE (Cellular Automation Finite Element) model coupling fluid flow, heat transfer, nucleation, and grain growth is developed and validated by comparing the results of both numerical simulations and physical experiments. The model successfully describes hydrodynamic fields generated by ultrasonic treatment and their influence on microstructural evolution. This validated model is then used to study the influence of the duration of ultrasonic treatment on temperature distribution and grain structure. A predominantly equiaxed grain structure developed due to the low temperature gradient throughout the melt is a result of the enhanced convection. These results highlight the critical role played by the convection induced by acoustic streaming during casting, that is, facilitating nucleation and grain growth.

Parametric resonance of a fluctuation fluid flow heat exchanger system

The tubes in a component-cooling water heat exchanger are frequently affected by shock waves that occur due to fluid flow in a nuclear power plant. Thus, the tubes often wear out. Such a fluid flow may alter the dynamic characteristics of a water heat exchanger and cause instability in it. In this study, the dynamics and instabilities in a component cooling water heat exchanger are examined. Because of the presence of fluid coupling between tubes, periodic tubes were used to realize a periodic coupling system. It is found that each tube is coupled to the adjacent tube through the fluid, and the system is weakly coupled. The dynamic equations of the heat exchanger system with consideration for the effect of fluid flow were derived using Galerkin method. Numerical results revealed that fluctuations in fluid flow may significantly affect the dynamics and instability of a component cooling water heat exchanger.

Effects of previously created fracture on the initiation and growth of subsequent fracture during TPMSF

Temporary plugging multi-cluster staged fracturing (TPMSF), using multi-cluster perforations and self-degradable diverting agents, is a novel technique to develop oil and gas reservoirs in deep wells. In this paper, the effects of previously created fractures on the initiation and growth of subsequent fracture were numerically investigated by utilizing XFEM-based CZM (i.e., cohesive zone model based on the extended finite element method). A 2D plane-plain model (coupling fluid flow and solid deformation) was established and truss model (truss elements distributed on the previous fracture surfaces) was used to maintain the different width of previously created fracture. Based on the model, multiple fracture simultaneous propagation was firstly simulated and then parametric studies were conducted for different fracture spacing, the propped width of the previous fracture, fracture created sequence, horizontal differential stress, Young’s modulus, and rock tensile strength. Numerical results show that multiple fractures cannot propagate uniformly because of fracture interaction even with equal flow rate distributions. During TPMSF, the propped width of the previous fracture, fracture spacing, and Young’s modulus primarily control the injection pressure of subsequent fractures; while rock tensile strength has a relatively weaker influence and horizontal stress contrast plays a negligible role. Moreover, the growth of subsequent fractures is dominated by fluid pressure, initial horizontal stresses and induced stresses.

Revised partial coupling in fluid–particulate systems

Fluid equations in Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) simulations solve the volume-averaged Navier–Stokes equations. Full coupling between the dispersed phase and continuous phase is made by the exchange of source terms as well as the void fraction. The void fraction is calculated from the presence of the particles in the computational fluid cells while the source terms are calculated from the point mass force models of the fluid–particle interaction forces. Dense particulate system with large spatiotemporal variations in the void fraction shows hard convergence behavior. This can impact the robustness of the solver during the time integration process. One option is to use partial coupling by neglecting the explicit effect of void fraction in the fluid momentum equations while retaining its effect on force models. Although the partial coupling is more stable and shows better convergence behavior, the mobility of the particles is found to be reduced as compared to the full-coupling approach. In the current work, we propose a revised partial coupling in which a modified fluid velocity is used in point mass force models to compensate for the omission of the void fraction in the fluid governing equations. The effectiveness of this method is demonstrated in a fluidized bed and in sediment transport simulations. In both cases it is shown that the use of the proposed method gives very good comparisons with the fully coupled simulations while reducing the fluid calculation time by factors ranging from 1.35 to 4.35 depending on the flow conditions. The revised partial coupling is not recommended as a substitute for full coupling in dense systems but as an alternate approach when full coupling leads to numerical difficulties.

Water surface wavelets

The current state of the art in real-time two-dimensional water wave simulation requires developers to choose between efficient Fourier-based methods, which lack interactions with moving obstacles, and finite-difference or finite element methods, which handle environmental interactions but are significantly more expensive. This paper attempts to bridge this long-standing gap between complexity and performance, by proposing a new wave simulation method that can faithfully simulate wave interactions with moving obstacles in real time while simultaneously preserving minute details and accommodating very large simulation domains. Previous methods for simulating 2D water waves directly compute the change in height of the water surface, a strategy which imposes limitations based on the CFL condition (fast moving waves require small time steps) and Nyquist's limit (small wave details require closely-spaced simulation variables). This paper proposes a novel wavelet transformation that discretizes the liquid motion in terms of amplitude-like functions that vary over space, frequency, and direction , effectively generalizing Fourier-based methods to handle local interactions. Because these new variables change much more slowly over space than the original water height function, our change of variables drastically reduces the limitations of the CFL condition and Nyquist limit, allowing us to simulate highly detailed water waves at very large visual resolutions. Our discretization is amenable to fast summation and easy to parallelize. We also present basic extensions like pre-computed wave paths and two-way solid fluid coupling. Finally, we argue that our discretization provides a convenient set of variables for artistic manipulation, which we illustrate with a novel wave-painting interface.

Numerical Simulation of V-shaped Segregation in Continuous Casting Blooms Based on a Microsegregation Model

This study establishes a volume-averaged model for transport phenomena to study V-shaped segregation in continuous casting blooms with different superheating and cooling rates by coupling fluid flow, macro-scale heat transfer, and solute transport. The results demonstrate that the modified Won–Thomas model considering back diffusion in the solid phase corresponds well with the measured carbon segregation. V-shaped segregation decreases with decreasing superheating and increases slightly with decreases in the cooling rate. The results of original position statistical distribution analysis correspond well with the simulation results. This phenomenon can be exploited to improve the quality of bloom.