Fluid Coupling Research Articles

Magnetohydrodynamic Calculation for Electromagnetic Stirring Coupling Fluid Flow and Solidification in Continuously Cast Billets

A new magnetohydrodynamic (MHD) model considering flow field and solidification is developed to simulate electromagnetic stirring (EMS) during billet continuous casting. Based on the model, the influence of fluid flow on the calculation of magnetic field, induced current, and electromagnetic force is investigated in comparison to the traditional calculation model. Furthermore, the characteristics of fluid flow affected by electromagnetic stirring, including three‐dimensional streamlines, tangential velocity, and meniscus fluctuation, are studied to evaluate the new MHD model. The MHD calculation reveals that the flow field in mold has a certain influence on the magnetic field, while the effect resulting from the interaction between flow field and magnetic field on the electromagnetic force is significant. As a consequence, increased velocity at the meniscus has been obtained compared to the traditional calculation, indicating a more intense meniscus fluctuation.

Discontinuous Finite Volume Element Method for a Coupled Non-stationary Stokes–Darcy Problem

In this paper, a discontinuous finite volume element method was presented to solve the nonstationary Stokes–Darcy problem for the coupling fluid flow in conduits with porous media flow. The proposed numerical method is constructed on a baseline finite element family of discontinuous linear elements for the approximation of the velocity and hydraulic head, whereas the pressure is approximated by piecewise constant elements. The unique solvability of the approximate solution for the discrete problem is derived. Optimal error estimates of the semi-discretization and full discretization with backward Euler scheme in standard $$L^2$$ -norm and broken $$H^1$$ -norm are obtained for three discontinuous finite volume element methods (symmetric, non-symmetric and incomplete types). A series of numerical experiments are provided to illustrate the features of the proposed method, such as the optimal accuracy orders, mass conservation, capability to deal with complicated geometries, and applicability to the problems with realistic parameters.

Modeling of Ti-W Solidification Microstructures Under Additive Manufacturing Conditions

Additive manufacturing (AM) processes have many benefits for the fabrication of alloy parts, including the potential for greater microstructural control and targeted properties than traditional metallurgy processes. To accelerate utilization of this process to produce such parts, an effective computational modeling approach to identify the relationships between material and process parameters, microstructure, and part properties is essential. Development of such a model requires accounting for the many factors in play during this process, including laser absorption, material addition and melting, fluid flow, various modes of heat transport, and solidification. In this paper, we start with a more modest goal, to create a multiscale model for a specific AM process, Laser Engineered Net Shaping (LENS™), which couples a continuum-level description of a simplified beam melting problem (coupling heat absorption, heat transport, and fluid flow) with a Lattice Boltzmann-cellular automata (LB-CA) microscale model of combined fluid flow, solute transport, and solidification. We apply this model to a binary Ti-5.5 wt pct W alloy and compare calculated quantities, such as dendrite arm spacing, with experimental results reported in a companion paper.

An incompressible immersed boundary solver for moving body flows using a cut cell discontinuous Galerkin method

Abstract We present a higher-order immersed boundary method (IBM) for moving body flows, based on a discontinuous Galerkin (DG) discretization. In our method bodies are represented by a sharp interface approach using cut cells. The position of the bodies and their velocity is prescribed by Newtons equation of motion. Furthermore, we introduce a splitting type approach of coupling fluid and rigid body solver and point out the explicit calculation of hydrodynamic forces using hierarchical moment fitting. To verify our method we compare our new approach to a range of numerical benchmarks taken from the literature. At first we compare our method with calculations using a body fitted grid. Thereafter we will focus on representing boundaries with fixed motion to point out the accuracy and flexibility of our IBM. Afterwards we show results of full coupled test cases in which the explicit coupling approach and the calculation of forces mentioned above come into play. It can be shown, that with our method we can get similar results by decreasing the number of total unknowns significantly, which is the main advantage of the proposed scheme.

Vertical jetting induced by shear horizontal leaky surface acoustic wave on 36° Y-X LiTaO3

Shear horizontal surface acoustic waves (SH-SAWs) have been regarded as good candidates for liquid sensing applications but are inefficient in fluid manipulation due to a minimal fluid coupling between the fluid and acoustic waves. However, in this letter, a vertical jetting function was realized using the SH-SAW generated from a 36° Y-X LiTaO3 SAW device. The jetting of the droplet induced by the SH-SAWs was observed nearly along the vertical direction, and the aspect ratio of the liquid beam is proportional to the applied power before breaking up, which is dramatically different from those generated from the conventional Rayleigh SAWs. By conducting theoretical simulation and experimental investigation on the SH-SAWs systematically, we concluded that the wave/energy pressure dissipated into the sessile droplets causes this vertical ejection on the device surface.

Frictional behaviour and friction mechanisms of rolling-sliding contact in mixed EHL

Frictional behaviour of mixed Elasto-hydrodynamic lubrication (EHL) arises from the coupling of the lubricant fluid and asperity interaction frictions. Due to the difficulties in modelling asperity interaction friction, existing approaches often use a constant friction coefficient obtained in boundary lubrication to approach the asperity interaction friction coefficient in mixed EHL. In this study, the asperity interaction friction is, for the first time, considered to result from either the boundary film friction or solid-to-solid ploughing and adhesion friction depending on the local contact and deformation conditions. The friction of mixed EHL was predicted by the combination result of lubricants fluid, boundary film, and solid-to-solid frictions. This development provides an alternative and cost effective method to estimate friction coefficient in mixed EHL.

Effect of Interdigitated Flow Field Geometry on Redox Flow Cell Performance

A large fraction of the cost of a flow battery installation comes from the high cost of separators and bipolar plates1. Optimizing the use of active area in flow batteries by maximizing power density allows cell stack engineers to reduce the amount of stack materials required. The design of flow fields has a significant impact on cell performance, including peak galvanic power density2,3. In this work, we present an experimental and computational study of interdigitated flow fields with varying dimensions. We demonstrate reduction of resistive and mass transport overpotential losses by altering the interdigitated flow field dimensions to reduce zones of mid-channel stagnant flow within the porous electrode. A two-dimensional model of an interdigitated flow field, coupling fluid dynamics and electrochemistry, is used to guide optimization of the channel, land, and electrode dimensions in the flow field. To study the influence of mass transport on performance, a flow cell is assembled with an unstructured, flow-through porous electrode, with a flat plate replacing the interdigitated flow field. Even with this simplified flow field, discrepancies persist between observed experimental results and predictions from porous electrode theory. We report our progress toward understanding and resolving these discrepancies. 1. V. Viswanathan et al., J. Power Sources, 247, 1040–1051 (2014) 2. M. L. Perry, R. M. Darling, and R. Zaffou, ECS Trans., 53, 7–16 (2013) 3. R. M. Darling and M. L. Perry, J. Electrochem. Soc., 161, A1381–A1387 (2014) Figure 1. Experimental results and computational predictions of overvoltages from a symmetric potassium ferrocyanide/ferricyanide flow cell using one of four different flow fields. The cell consists of one sheet of SGL 39-AA on each side of a Nafion 212 membrane. The active area of each flow field is 5 cm2. Figure 1

Simulation of convective flow and thermal conditions during ultrasonic treatment of an Al-2Cu alloy

Grain refinement of an Al-2Cu alloy using ultrasonic treatment was investigated numerically. A finite element model coupling fluid flow and heat transfer was 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 its influence on heat transfer. The simulations were used to study the influence of the duration of ultrasonic treatment and the associated acoustic streaming on convection and the resulting temperature distribution. It was revealed that a relatively cold sonotrode applied during ultrasonic treatment for up to 4 min created a casting environment that promoted crystal nucleation and enabled their growth and survival during transport of these grains into the bulk of the melt by strong convection. The enhanced convection established a low temperature gradient throughout the melt which favours the formation of an equiaxed grain structure. Therefore, the convection induced by acoustic streaming plays a critical role in facilitating nucleation, growth, and transport of grains.

Calculation and analysis of complex fluid flow and thermal fields in a fully air-cooled hydrogenerator

Fully air-cooled hydrogenerators are applied widely in power stations because of advantages such as high efficiency, simple structure, and easy maintenance. This study investigated fully air-cooled hydrogenerators, and a three-dimensional fluid and thermal coupling analysis model of a hydrogenerator was proposed. Using the finite volume method, the changes in complex fluid velocity in the stator and rotor zones at different times were determined. Additionally, temperature changes in metal parts and insulation in the hydrogenerator were investigated with respect to time from the start to steady state operation of a hydrogenerator. In the study, the time required for the temperatures of different hydrogenerator parts to reach a steady state was predicted. Following the starting of the hydrogenerator, the temperature distribution of different parts at the same time and the changes in the temperature distribution of parts at different times were determined in the hydrogenerator. The surface heat-transfer coefficient distribution law on the surfaces of rotor exciting winding was studied. The calculated temperature result was compared with the measured value, and the results indicated that the calculated value of temperature agreed well with the measured value. Thus, the study indicated the feasibility of designing a fully air-cooled hydrogenerator from a thermal analysis viewpoint.

On coupling fluid plasma and kinetic neutral physics models

The coupled fluid plasma and kinetic neutral physics equations are analyzed through theory and simulation of benchmark cases. It is shown that coupling methods that do not treat the coupling rates implicitly are restricted to short time steps for stability. Fast charge exchange, ionization and recombination coupling rates exist, even after constraining the solution by requiring that the neutrals are at equilibrium. For explicit coupling, the present implementation of Monte Carlo correlated sampling techniques does not allow for complete convergence in slab geometry. For the benchmark case, residuals decay with particle number and increase with grid size, indicating that they scale in a manner that is similar to the theoretical prediction for nonlinear bias error. Progress is reported on implementation of a fully implicit Jacobian-free Newton–Krylov coupling scheme. The present block Jacobi preconditioning method is still sensitive to time step and methods that better precondition the coupled system are under investigation.

Numerical schemes for the coupling of compressible and incompressible fluids in several space dimensions

We present a numerical scheme for immiscible two-phase flows with one compressible phase and one incompressible phase. Special emphasis lies in the discussion of the coupling strategy for compressible and incompressible Euler equations to simulate inviscid liquid–vapor flows. To reduce the computational effort further, we also introduce two approximate coupling strategies. The resulting schemes are compared numerically to a fully compressible scheme and show good agreement with these standard algorithm at lower numerical costs.

Numerical Investigation of Fluid Flow and Performance Prediction in a Fluid Coupling Using Large Eddy Simulation

Large eddy simulation (LES) with various subgrid-scale (SGS) models was introduced to numerically calculate the transient flow of the hydraulic coupling. By using LES, the study aimed to advance description ability of internal flow and performance prediction. The CFD results were verified by experimental data. For the purpose of the description of the flow field, six subgrid-scale models for LES were employed to depict the flow field; the distribution structure of flow field was legible. Moreover, the flow mechanism was analyzed using 3D vortex structures, and those showed that DSL and KET captured abundant vortex structures and provided a relatively moderate eddy viscosity in the chamber. The predicted values of the braking torque for hydraulic coupling were compared with experimental data. The comparison results were compared with several simulation models, such as SAS and RKE, and SSTKW models. Those comparison results showed that the SGS models, especially DSL and KET, were applicable to obtain the more accurate predicted results than SAS and RKE, and SSTKW models. Clearly, the predicted results of LES with DSL and KET were far more accurate than the previous studies. The performance prediction was significantly improved.

Multiscale Thermal Hydraulic Study under the Inadvertent Safety Injection System Operation Scenario of Typical Pressurized Water Reactor

The Reactor Pressure Vessel (RPV) inlet nozzles and downcomer wall in Pressurized Water Reactors (PWR) may suffer serious thermal shock caused by cold water from reactor Safety Injection System (SIS) in some unexpected accident scenarios. It implies the formation of great temperature gradient on the inlet nozzles and RPV wall, leading to the localized stresses and propagation of possible flaws that appeared in the material. In this paper, the multiscale thermal hydraulic analysis was performed for Chashma Nuclear Power Plant (NPP) under the inadvertent SIS operation scenario. The primary loop and SIS were modeled using one-dimensional method, while the three-dimensional models of reactor cold leg, RPV inlet nozzles, and downcomer were established. Then, the inadvertent Safety Injection System operation scenario was simulated using RELAP5 code, providing the boundary conditions for three-dimensional Computational Fluid Dynamics (CFD) analysis. The fluid and solid coupling heat transfer simulation method was employed. Results show that the maximum temperature difference was about 80 K in the most conservative condition and the RPV inlet nozzle region was the most critical region during the accident. This work could provide in-depth understanding on the effect of cold coolant injection along the main pipes and RPV wall during the accident scenario.

Ultrasonic Inspection and Data Analysis of Glass- and Carbon-Fibre-Reinforced Plastics

Non-destructive testing (NDT) helps to find material defects without having an influence on the material itself. It is applied as a method of quality control, for online structural health monitoring, and for inspection of safety related components. Due to the ability of automation and a simple test setup ultrasonic testing is one major NDT technique next to several existing options. Whereas contact technique allows the use of higher frequencies of some MHz and phased array focusing, air-coupled ultrasonic testing (ACUT) shows different advantages. Most significant for ACUT is the absence of any coupling fluid and an economical test procedure respective time and costs. Both contact technique and ACUT have been improved and enhanced during the past years. One important enhancement is the development of airborne transducers based on ferroelectrets, like charged cellular polypropylene (cpp), which makes the application of any matching layers being mandatory in conventional piezoelectric transducers unnecessary. In this contribution we show ultrasonic inspection results of specimens made of carbon- and glass-fibre-reinforced plastic. These specimens include defects represented by drill holes and artificial delaminations of various size and depth. We compare inspection results achieved by using contact technique to those achieved by ACUT. For ACUT, conventional piezoelectric transducers and transducers based on cpp were used, both focused as well as non-focused types. Contact inspections were performed with a multi-channel matrix array probe. Once the inspection data is recorded it can be analysed in order to detect and evaluate defects in the specimen. We present different analysing strategies and compare these regarding detection rate and sizing of defects.

FE-simulation of the Cutting Process under Consideration of Cutting Fluid

High pressure lubricoolant supply has mechanical and thermal effects on chip formation in cutting processes. Until now, chip formation simulations are mainly performed without consideration of coolant. This paper presents a 2D FE-model coupling fluid simulation and structure simulation through a novel fluid-structure interaction (FSI) in one simulation model. The chip formation simulation is based on a coupled Eulerian-Lagrangian (CEL) formulation. The Johnson-Cook material and damage model have been used for serrated chip formation of TiAl6V4. Based on this model the effects of coolant application on chip formation were investigated in experiments and simulations.

自動車用トルクコンバータのロックアップクラッチの動特性解析

The torque converter is a kind of fluid coupling that is widely used as a start-up device for automobiles equipped with an automatic transmission. A lock-up clutch is often incorporated in the torque converter in order to improve vehicle fuel economy in the higher speed ratio range. This improvement is obtained because the lock-up clutch can reduce fluid losses by engaging the input and output shafts to rotate at relative speeds with only a small amount of slip. Operation of the lock-up clutch is controlled mainly by supply and discharge oil pressure of the torque converter. The purpose of this study was to better understand clutch behavior under the influence of oil flow. Flow through the lock-up clutch was computed by using a commercial CFD code at three speed ratios of 0.8, 1.0 and 1.2 under the prescribed supply and discharge oil pressure sequence. Unsteady computations were conducted under the assumption that the flow was weakly coupled with the solid mass motion. Quasi-steady computations were also conducted under the assumption that a dynamically equilibrium state was maintained when the clutch moved. The results showed that the response time of the lock-up clutch increased with a higher speed ratio and that flow through the clutch changed directions from outward to inward in the engagement process in all cases. The computed response time coincided reasonably well with the experimental data obtained with the actual machine. It was also found that the quasi-steady analysis results showed an unreasonable or meaningless tendency regarding the response time.

Fluid and structure coupling analysis of the interaction between aqueous humor and iris.

BackgroundGlaucoma is the primary cause of irreversible blindness worldwide associated with high intraocular pressure (IOP). Elevated intraocular pressure will affect the normal aqueous humor outflow, resulting in deformation of iris. However, the deformation ability of iris is closely related to its material properties. Meanwhile, the passive deformation of the iris aggravates the pupillary block and angle closure. The nature of the interaction mechanism of iris deformation and aqueous humor fluid flow has not been fully understood and has been somewhat a controversial issue. The purpose here was to study the effect of IOP, localization, and temperature on the flow of the aqueous humor and the deformation of iris interacted by aqueous humor fluid flow.MethodsBased on mechanisms of aqueous physiology and fluid dynamics, 3D model of anterior chamber (AC) was constructed with the human anatomical parameters as a reference. A 3D idealized standard geometry of anterior segment of human eye was performed. Enlarge the size of the idealization geometry model 5 times to create a simulation device by using 3D printing technology. In this paper, particle image velocimetry technology is applied to measure the characteristic of fluid outflow in different inlet velocity based on the device. Numerically calculations were made by using ANSYS 14.0 Finite Element Analysis. Compare of the velocity distributions to confirm the validity of the model. The fluid structure interaction (FSI) analysis was carried out in the valid geometry model to study the aqueous flow and iris change.ResultsIn this paper, the validity of the model is verified through computation and comparison. The results indicated that changes of gravity direction of model significantly affected the fluid dynamics parameters and the temperature distribution in anterior chamber. Increased pressure and the vertical position increase the velocity of the aqueous humor fluid flow, with the value increased of 0.015 and 0.035 mm/s. The results act on the iris showed that, gravity direction from horizontal to vertical decrease the equivalent stress in the normal IOP model, while almost invariably in the high IOP model. With the increased of the iris elasticity modulus, the equivalent strain and the total deformation of iris is decreased. The maximal value of equivalent strain of iris in high IOP model is higher than that of in normal IOP model. The maximum deformation of iris is lower in the high IOP model than in the normal IOP model.ConclusionThe valid model of idealization geometry of human eye could be helpful to study the relationship between localization, iris deformation and IOP. So far the FSI analysis was carried out in that idealization geometry model of anterior segment to study aqueous flow and iris change.

Characteristics and formation mechanism of Changxing Formation-Feixianguan Formation reef-shoal reservoirs in Yuanba Gasfield

AbstractTaking advantage of the successful experience in exploring and discovering the Puguang Gasfield, and targeting the Changxing Formation-Feixianguan Formation organic reef and shoal lithological trap, SINOPEC drilled Well Yuanba 1 in the Bazhong area in Northeast Sichuan in 2006, and discovered the Yuanba Gasfield with a high-production commercial gas flow of 503×103m3/d. As a normal-pressured lithological gas reservoir with high H2S content, Yuanba Gasfield is characterized by weak tectonic deformation and deep burial, with an average depth of 6,600m in the central part of the gas reservoir, and is the deepest marine gas field in the Sichuan Basin. Yuanba Gasfield is dominated by large-scale reef-shoal reservoirs of Changxing Formation. The formation of the reservoirs was primarily controlled by early meteoric freshwater dissolution and dolomitization, and less affected by deep-burial dissolution and tectonic movement. A comparative analysis was made on the characteristics of deep reef-shoal reservoirs in the Yuanba and Puguang gas fields so as to explore their formation mechanisms. It is concluded that the reservoir size and early pore development was controlled by early depositional-diagenetic environment. Fracture formation and dissolution were controlled by structure–fluid coupling, pore reworking and preservation is determined by fluid–rock interaction.

Dynamic coupling of phase-heat and mass transfer in porous media and conjugate fluid/porous domains

A dynamically varying technique for phase heat and mass transfer in porous media and fluid/porous domains has been developed and incorporated into a conjugate finite volume CFD framework. The local interstitial phase mass exchange within porous zones is estimated by comparison of the resistances to moisture transport within the solid and void constituents of the porous material; the higher resistance expression being used as rate-determining. Based on the mass transfer expression, a local estimate of the Biot number is used to physically apportion the withdrawal of vaporization energy from the solid and fluid constituents of the porous medium. A similar approach is used for coupling of the clear fluid and porous CFD cells at the clear fluid/porous interface. A phase ratio concept is introduced at these interfaces to be able to couple the different phases in heat and mass transfer. The model is generic, involving details that allow application to a wide range of cases and is one of the least empirically-adjusted models. The microscopic coupling approach has been validated for Coal packed bed drying. Results show good agreement with experimental data in terms of the matching trends and the small margins for temporal moisture and temperature variation. The macroscopic coupling technique has been tested using the cases of drying of an apple slice and the dehydration of mineral plaster. Investigating the two cases showed a clear difference in behavior as the apple slice case is material-side-resistance dominant – i.e. diffusively dominant – and the plaster case is air-side-resistance dominant – i.e. convectively dominant. The results are physically reasonable and compare well to available experiments and reported results from the literature. The comparisons indicate the capability of the present approach to model the dynamic coupling accurately in a computationally time-efficient manner.

Comparative analysis on spatiotemporal pore pressure evolution under surface–wave perturbations

The near surface spatiotemporal pore pressure fluctuations in a porous half space induced by seismic surface–wave perturbations in different poroelastic regimes are analytically compared. The results for the pore pressure in the space–time domain are derived by inverse transforms of the fundamental solutions of dynamic poroelasticity in the frequency–wavenumber domain. Different poroelastic regimes depend on the different low frequency approximation for Biot's multi wave mode physical behaviors. In low seismic frequency band, whereas the fast wave mode inference can generate surface wave along the interface, fluid pressure is also significantly perturbated as in solid phase, but behaves as a slow P2 mode reflected by the R surface wave. It is also shown that the amount of induced pore pressure fluctuations are different by P2 diffusivity (dispersion–difusivity regime, DD and non–dispersion–diffusivity regime, NDD) and P2 wave (full–wave regime, FW). The strong solid and fluid coupling on the interface generates the transferred RP2 mode. Therefore, the decoupled viscoleastic approximation (VA) does not represent these near surface fluid characteristics. The results can be applied to predict near surface pore pressure responses under seismic perturbations, or as a benchmark for other numerical approaches for pressure solutions in a dynamic poroelastic half space, and also favor a potential interpretation for near surface soil liquefaction failure.