Fluid Coupling Research Articles

Spin-thermal shear coupling in a relativistic fluid

We show that spin polarization of a fermion in a relativistic fluid at local thermodynamic equilibrium can be generated by the symmetric derivative of the four-temperature vector, defined as thermal shear. As a consequence, besides vorticity, acceleration and temperature gradient, also the shear tensor contributes to the polarization of particles in a fluid. This contribution to the spin polarization vector, which is entirely non-dissipative, adds to the well known term proportional to thermal vorticity and may thus have important consequences for the solution of the local polarization puzzles observed in relativistic heavy ion collisions.

Study on Negative Corona Discharge of the Small Spherical Metal Electrode

The negative corona discharge between a small spherical metal electrode (SSME) and a grounded plane electrode (GPE) was often a concern. The ring mode discharge and the dot mode discharge were found in the experimental study. Up until now, these two phenomena are not verified in simulation study. Simulation on the negative corona discharge between an SSME and a GPE is staged in this article. The pulse currents in negative corona discharge are analyzed under different voltages, radius of the SSME, and gap distance coupling fluid dynamic equations and Poisson equation based on the axisymmetric model. The interesting phenomenon found is that the corona discharges sequentially happen at different central angles on the surface of the SSME starting with the point nearest to the GPE. The negative corona discharges generated by the SSME and the hemispherical metal electrode are compared. The mechanism of discharge is analyzed by comparing their current pulses, electric field intensities, and changes in the concentration of ions. The ring mode discharge and the dot mode discharge are shown in our simulation. The reason for the formation of the ring mode discharge is also given.

A dual porosity poroelastic model for simulation of gas flow in saturated claystone as a potential host rock for deep geological repositories

Claystone is considered as a potential host rock for radioactive waste disposal at great depth in many countries. Considerable quantity of gas can be generated in a deep geological repository (DGR) due to several processes, which may affect the integrity of the host rock and the safety of the DGR. Thus, understanding the migration of gas through the host rock is an essential requirement in developing a safety case for a deep geological disposal of radioactive waste. In this paper, a fully coupled dual porosity poroelastic model is developed to simulate the gas transport process in initially saturated claystone. The model considers the hydro-mechanical behavior for the fractured porous medium consisting of both the porous matrix (represented by the porous continuum) and fractures (represented by the fractured continuum), which are two separate and overlapping porous media. Each continuum has its own constitutive law that imposes a superimposed effect on the behavior of the fractured porous medium. The mechanical coupling between the two continua is through total stress equilibrium and strain superimposition technique, while the fluid coupling in the two continua is through water exchange term and porosity interaction. The capability of the developed dual porosity poroelastic model is evaluated by comparing the simulated results with that recorded in the laboratory gas injection tests on claystone, in which the main experimental behaviors, i.e., the major gas breakthrough, sample volume dilation, gas induced fracturing are well represented.

RESEARCH ON PARTICLE SWARM COLLISION SEARCH AND ADVANCEMENT ALGORITHM FOR CFD-DEM COUPLING DOMAIN SOLVING

When the computational fluid dynamics discrete element method (CFD-DEM) is used for solid-liquid two-phase coupling analysis, the selection of particle calculation time step directly affects the accuracy and efficiency of the coupling calculation. For this reason, each target particle is selected as the research object, and interpolation function is introduced to calculate the motion displacement of the time step, and a variable spatial search grid is constructed. An improved particle collision search algorithm (modified discrete element method, MDEM) was proposed by selecting possible collision particles to build a search list and using reverse search Method to judge collision particles. The algorithm in particle group and fluid coupling calculation, the particle counting the initial time step selection particle collision time without limit, realization of automatic adjustment and correction by large step, calculated by the real-time update of fluid particles and fluid coupling conditions, time step, the granular computing time step selection, as a result of low computational efficiency, selection is too large too small to solve the problem of false negatives, particle collision of particles and fluid coupling numerical simulation provides a effective calculation method. Through the numerical simulation of two particles and multiple particles, the relative errors of the collision forces, collision positions and times between particles obtained are all less than 2% compared with the theoretical calculation results. Compared with the traditional DEM collision search algorithm, the three calculation time steps selected do not affect the calculation accuracy, and the calculation efficiency is higher. Through the coupling numerical simulation of multiple particles and fluid, using the traditional CFD-DEM method, the precise solution can be obtained only when the particle calculation time step is 10$^{-6}$ s or smaller, while the precise solution can be obtained by using the proposed method to take 10$^{-4}$ s, which avoids the problem of missed decision caused by particle collision with the increase of time step, and the calculation time is reduced by 16.7%.

Study on vehicle drag reduction simulation based on Suzen–Huang model

In the past numerical simulation of plasma and fluid coupling, the usually used Suzen numerical simulation model has the defect that the error increases with the increase in excitation voltage. The static test of the ionic wind is used to modify the parameters of the Suzen simulation model, and it applied the modified Suzen model to the flow control of the automobile external flow field, which shows good consistency with the wind tunnel test results. Results show that the Suzen model modified by the static test results of the ionic wind is suitable for different excitation voltage conditions. The corrected body force and charge density distribution conform to the change trend of plasma discharge, and the error between the maximum ionic wind velocity obtained by simulation and the test result is within 4%; the modified Suzen model is successfully applied to the plasma flow control of automobile aerodynamic drag reduction. The results show that the exciter suppresses the generation of periodic separation vortices in the tail of the model, which makes the vorticity in the wake significantly decrease, thereby reducing the energy dissipation and the aerodynamic drag of the model. Through the research in this paper, the modified Suzen model reduces the simulation error. Plasma flow control technology is applied to the field of automobile aerodynamic drag reduction, which has accumulated important experience methods and data foundation for the engineering application of this technology. It also provides new methods for improving vehicle aerodynamic performance and fuel economy.

Heat transfer efficiency of hierarchical corrugated sandwich panels

As a kind of biomimetic materials, ultralight hierarchical porous structures possessing excellent mechanical properties such as load bearing, impact energy absorption, vibration reduction and noise attenuation have been exploited. Often, these porous structures exhibit continuous flow passages that allow for cooling fluids to pass through, thus enabling simultaneous load-bearing and active heat dissipation. This study investigated the convective cooling efficiency of a sandwich panel with hierarchical corrugated core subjected to heating from the face sheets and active cooling through the core. Built upon the classical fin approach, a theoretical model coupling wall heat conduction and fluid convection in the core was established for the hierarchical corrugated-core sandwich panel, covering the full range of fluid flow (from laminar, transition to turbulent). The theoretical model predictions were validated against full numerical simulations. Based on the theoretical model, an artificial intelligence optimization method (i.e., the ant colony algorithm) was adopted to find the optimal combination of key independent geometric parameters of the sandwich panel for maximized heat transfer performance. For the problem of multi-variables optimization, it was demonstrated that the ant colony algorithm is superior in terms of computational time to the traditional exhaustive search method. For a given pressure drop, a set of optimum geometric parameters corresponding to maximum cooling efficiency was found for the proposed hierarchical corrugated-core sandwich panel.

On the treatment of hydroelastic slamming by coupling boundary element method and modal superposition method

An efficient fluid and structure interaction (FSI) coupling strategy between boundary element method, i.e. BEM (fluid part), and modal superposition method (structure part) is proposed to study hydroelastic slamming of wedge sections. The coupling strategy possesses simplicity in coding construction by transmission of coordinates, velocity and pressure on the fluid-solid interface. Convergence property of grid size, time step and modal number are first investigated. After that, the accuracy of the model is verified by comparing the numerical results with published ones. Hydroelastic effect associated with plate thickness, deadrise angle, impact velocity and boundary condition is discussed by the comparison between quasi-static, decoupling and coupling solutions, where quasi-static and decoupling solutions are established by neglecting the influence of elastic response of structure on the water flow field. The results show that quasi-static solution underestimates structural maximum response under specified hydroelastic parameters, and a time-lag effect is found between results of decoupling and coupling solutions.

Multi-objective optimization of composite regeneration performance of a CeO2-based catalyzed diesel particulate filter

ABSTRACT The catalyzed diesel particulate filter (CDPF) is one of the best methods used to control the particulate matter from internal combustion engine. CeO2 is used as the catalyst in the CDPF due to its good redox capacity, oxygen storage capacity and anti-oxidation capacity to NOx. However, there are few studies on the effect of key factors on composite regeneration performance of CeO2-based CDPF. Therefore, a single-channel numerical model was established in this study by coupling fluid flow, mass transfer, heat transfer and chemical mechanism. In order to save computing time and computing resources, a sample space of the simulated data from the model was established by optimal space-filling method to build a surrogate model by response surface methodology. A multi-objective optimization on the composite regeneration performance of CDPF was carried out, in which the inlet NOx concentration, inlet temperature, catalyst coated amount and the N2O concentration, soot regeneration rate, pressure drop, NOx reduction rate, and peak temperature for coated catalyst are set as the design and optimization variables, respectively. Results show that the optimum inlet NOx concentration, inlet temperature and catalyst coated amounts are 0.106 mol/m3, 761.798 K and 0.428 mm, respectively. The findings of this study give useful insights into the operation of CDPF and the thermal management of after-treatment systems.

Differentiable Fluids with Solid Coupling for Learning and Control

We introduce an efficient differentiable fluid simulator that can be integrated with deep neural networks as a part of layers for learning dynamics and solving control problems. It offers the capability to handle one-way coupling of fluids with rigid objects using a variational principle that naturally enforces necessary boundary conditions at the fluid-solid interface with sub-grid details. This simulator utilizes the adjoint method to efficiently compute the gradient for multiple time steps of fluid simulation with user defined objective functions. We demonstrate the effectiveness of our method for solving inverse and control problems on fluids with one-way coupled solids. Our method outperforms the previous gradient computations, state-of-the-art derivative-free optimization, and model-free reinforcement learning techniques by at least one order of magnitude.

Non-contact photopyroelectric approach for complete thermal characterization of porous building materials

The suitability of two photopyroelectric (PPE) methods for measuring the thermal diffusivity and effusivity of porous solids is described. The main characteristic of both methods, associated with the possibility of investigating porous solids, is the absence of coupling fluid between the pyroelectric sensor and sample. The first method (proposed initially by Salazar et al., Measurement 121, 96 (2018) [1]) relies on the front detection configuration with opaque pyroelectric sensor and thermally thick sample. Based on the phase frequency scan of the PPE signal, this method leads to the direct measurement of the sample’s thermal effusivity. The second method (proposed initially by Zammit et al., J. Appl. Phys. 117, 105,104 (2015) [2]) is based on two successive measurements (frequency scans), one in back and one in front PPE configuration, followed by a self-normalization of the phase vs. modulation frequency dependence. This method uses transparent pyroelectric sensor and backing material, allowing the direct measurement of the sample thermal diffusivity. In the paper, both methods were adapted and improved for investigating some porous building materials of interest: old bricks with unknown values of thermal parameters.

Stabilization of a smoothed finite element semi-implicit coupling scheme for viscoelastic fluid–structure interaction

We propose in this work a stabilization approach for semi-implicit coupling of viscoelastic fluid–structure interaction (VFSI) using the cell-based smoothed finite element method (CS-FEM). The viscoelastic fluid and nonlinear solid equations are spatially discretized by the CS-FEM and then are semi-implicitly coupled via a partitioned solution strategy. The current semi-implicit coupling framework depends on a second-order characteristic-based split (CBS(B)) scheme that solves the Navier–Stokes equations together with the Oldroyd-B constitutive model in the fractional-step manner. To enhance the stability of the semi-implicit coupling algorithm, the discrete elastic-viscous split stress-gradient (DEVSS-G) procedure is introduced into the explicit stage while the stabilized pressure gradient projection (SPGP) is earmarked for the implicit stage. Moreover, the iterated end-of-step velocity begins with the intermediate velocity during the subiterations. The DEVSS-G/CBS(B)-SPGP technique is readily applied to the CBS-based partitioned semi-implicit coupling algorithm for VFSI. Visible improvements in stabilization and efficiency are revealed in a benchmark test. • A semi-implicit coupling scheme is proposed for viscoelastic fluid–structure interaction. • DEVSS-G/CBS(B)-SPGP stabilization is presented for the semi-implicit scheme. • VFSI system is entirely formulated by cell-based smoothed finite element method. • The developed technique boosts the stability and efficiency considerably.

Evaluation of the sound reduction index of flat panels through FE models accounting for fluid-structure interaction: Stochastic versus plane wave superposition methods

This work presents an efficient procedure to predict the sound reduction index (SRI) of a flat panel of arbitrary internal complexity starting from numerical finite element (FE) simulations. This hybrid analytical-FE procedure allows to perform narrow band calculations considering fluid coupling up to high frequencies. The exciting sound field is synthesised considering a series of uncorrelated plane waves impinging on the panel. A stochastic approach based on the sinc function is also considered. A test case is presented in which the hybrid approach is applied to a glass panel. Computation time and memory consumptions are compared for the different implementations, showing that the stochastic approach requires considerably larger resources than the plane wave formulations. The method is validated against predictions by analytical methods and experimental data from sound transmission suites. To match the experimental results, the angle of incidence is limited to the value of 75∘, whose origin is discussed by means of ray-tracing simulations of the sound field distribution in the source room. It is found that the quality of the predictions can be improved by including the actual characteristics of the sound field in the plane wave formulation. If compared to a commercial full FE software, the proposed hybrid procedure features greatly reduced computational time, and results closer to the experimental values in the entire frequency range of interest.

Theoretical and experimental study of bulge formation in laser polishing of 304 stainless steel

Abstract As an emerging surface treatment process, laser polishing is dedicated to reducing the surface roughness of the sample, but some new surface structures (such as ripples, undercuts, bulges, step structures, and martensite needles) may be introduced into the polished surface, affecting the effect of laser polishing. This work aims to reveal the formation mechanism of bulges in the center of the polished track. The effect of laser polishing process parameters on the size parameters of bulges was studied through experiments of laser polishing. And a two-dimensional numerical model was developed by coupling heat transfer and fluid flow. The evolution of bulges, the temperature field, and the velocity field was presented with this model. Furthermore, through the analysis of the surface forces and surface velocities of the molten pool, it was found that the thermocapillary force affected by surface-active elements (oxygen, sulfur, and phosphorus) is the main driving force for the formation of bulges. And some measures to reduce or eliminate bulges were proposed to improve the surface finish of laser polishing. In addition, the final surface profile of the bulges after laser polishing was simulated, which was in good agreement with the experimental results. And this model can be extended to predict the evolution of surface topography in laser polishing, guiding the optimization of process parameters in laser polishing.

Torque Converter Launch and Lock with Multi-Input Multi-Output Control

<div class="section abstract"><div class="htmlview paragraph">A torque converter is a type of fluid coupling device used to transfer engine power to the gearbox and driveline. A bypass clutch equipped in a torque converter assembly is a friction element which when fully engaged, can directly connect the engine to the gearbox. The torque converter is an important launch device in an automatic transmission which decouples engine speed from gearbox input speed while providing torque multiplication to drive the vehicle. During partial pedal launch, it is desired to engage the bypass clutch early and reduce the converter slippage in order to reduce power loss and achieve better fuel economy. However, engaging the bypass clutch early and aggressively may disturb the wheel torque and cause unpleasant driving experiences. This paper describes a multi-input multi-output (MIMO) control method to coordinate both engine and converter bypass clutch to simultaneously deliver desired wheel torque and reduce converter slippage. The proposed control method leverages a feedforward control derived from a standard converter hydrodynamic model and a Linear-quadratic regulator (LQR) feedback control. It considers the desired gearbox input torque and converter slippage as two control targets and engine torque and bypass clutch capacity as two control inputs to achieve the targets. This method enables aggressive converter lock-up without degrading driveability and will potentially improve calibration efficiency.</div></div>

Fluid-cloth coupling algorithm based on PBD and CCD

In order to simulate the interaction between cloth and fluid, we use Smooth Particle Hydrodynamics (SPH) as a method in fluid simulation, we propose a Continuous collision detection (CCD) and position-based dynamics (PBD) collision constrained iterative flow coupling method. By analyzing the parallelism of the algorithm, we implement a low storage and load balanced fluid and cloth coupling algorithm parallel computing is used to accelerate the simulation. The experimental results show that our method realizes the bidirectional coupling of fluid and cloth, and improves the simulation performance.

Energy Efficiency Analysis of Copper Ore Ball Mill Drive Systems

Milling is among the most energy-consuming technological stages of copper ore processing. It is performed in mills, which are machines of high rotational masses. The start of a mill filled to capacity requires appropriate solutions that mitigate the overloading. One method for increasing the energy efficiency of ball mills is to optimize their drive systems. This article looks at two variants of drive systems with efficiencies higher than the already existing solutions. The first variant is a low-speed synchronous motor with permanent magnets without a gearbox, and the second variant is an asynchronous high-efficiency motor with a gearbox and a fluid coupling. The energy performance analysis of the three solutions was based on the average energy consumption indicator per mass unit of the milled material and on the energy consumption per hour. The investigations required models of the drive systems and analyses with the use of the Monte Carlo methods. The highest energy efficiency is observed in the case of the solution based on the permanent magnet motor. However, the drive system with the high-speed motor offers a gentle start-up possibility owing to the fluid coupling.

Multi-phase lattice Boltzmann (LB) simulation for convective transport of nanofluids in porous structures with phase interactions

PurposeA combination of highly conductive porous media and nanofluids is an efficient way for improving thermal performance of relevant applications. For precisely predicting the flow and thermal transport of nanofluids in porous media, the purpose of this paper is to explore the inter-phase coupling numerical methods.Design/methodology/approachBased on the lattice Boltzmann (LB) method, this study combines the convective flow, non-equilibrium thermal transport and phase interactions of nanofluids in porous matrix and proposes a new multi-phase LB model. The micro-scale momentum and heat interactions are especially analyzed for nanoparticles, base fluid and solid matrix. A set of three-phase LB equations for the flow/thermal coupling of base fluid, nanoparticles and solid matrix is established.FindingsDistributions of nanoparticles, velocities for nanoparticles and the base fluid, temperatures for three phases and interaction forces are analyzed in detail. Influences of parameters on the nanofluid convection in the porous matrix are examined. Thermal resistance of nanofluid convective transport in porous structures are comprehensively discussed with the models of multi-phases. Results show that the Rayleigh number and the Darcy number have significant influences on the convective characteristics. The result with the three-phase model is mildly larger than that with the local thermal non-equilibrium model.Originality/valueThis paper first creates the multi-phase theoretical model for the complex coupling process of nanofluids in porous structures, which is useful for researchers and technicians in fields of thermal science and computational fluid dynamics.

Achieving complete reaction while the solid volume increases: A numerical model applied to serpentinisation

Solid volume increases during the hydration of mantle rocks. The fluid pathways necessary to feed the reaction front with water can be filled by the low density reaction products. As a result, the reaction front dries out and the reaction stops at low reaction progress. This process of porosity clogging is generally predicted to dominate in reactive transport models, even when processes such as reaction-induced fracturing are considered. These predictions are not consistent with observations at mid-ocean ridges where dense mantle rocks can be completely replaced by low density serpentine minerals. To solve this issue, we develop a numerical model coupling reaction, fluid flow and deformation. High extents of reaction can only be achieved when considering that the increase in solid volume during reaction is accommodated through deformation rather than porosity clogging. The model can generate an overpressure that depends on the extent of reaction and on the boundary conditions. This overpressure induces viscoelastic compaction that limits the extent of the reaction. The serpentinisation rate is therefore controlled by the accommodation of volume change during reaction, and thus by deformation, either induced by the reaction itself or by tectonic processes.

Geochemistry of vapor-dominated hydrothermal vent deposits in Yellowstone Lake, Wyoming

Yellowstone Lake hydrothermal vent systems have been studied using ROV assets to better understand the chemical and mineralogical evolution of the sublacustrine sediments through which the hot spring fluids discharge to the lake floor. Here we focus on the deposits/alteration and coexisting vent fluid chemistry associated with the Deep Hole on the lake floor, east of Stevenson Island. Remote in its location, at 120 m below the lake surface, this region in the northeast portion of Yellowstone Lake is associated with numerous hydrothermal vents and hot springs, providing evidence of high-temperature fluid-mineral interaction and phase separation phenomena. Vapor-dominated hydrothermal fluids issuing from Deep Hole vents attain temperatures in excess of 150 °C and are enriched in magmatically derived H2S and CO2. Upon mixing with lake water in the root zone of the hydrothermally active vents, the dissolved gases render the mixed fluid, both acidic and reducing, effectively transforming diatomaceous sediment, with detritally sourced Al and Fe components, to an alteration assemblage dominated by kaolinite, pyrite, and lesser boehmite. These alteration processes have been modeled by computer based simulations, coupling fluid flow and mineral dissolution kinetics, to provide insight on the temporal evolution of the vent system. Results predict rapid dissolution of amorphous silica. The magnitude and rate of silica loss, facilitated by the continuous influx of acidic source fluids, yields an increasingly silica poor alteration mineral sequence with time, characterized by quartz, followed by kaolinite and ultimately boehmite. These data are consistent with the observed decrease in SiO2/Al2O3 ratio of the vent deposits with increasing abundance of trace immobile elements, suggesting significant mass loss with reaction progress. Pyrite is predicted to form from sulfidation of magnetite, with noteworthy decrease in magnetic intensity, as measured for hydrothermally altered sediment in the near-field vent environment. Moreover, hydrogen isotope compositional data for kaolinite, together with δD vent fluid data, suggest temperatures in keeping with the high temperatures measured for the vent deposits and discharging fluid, while supporting the potential use of kaolinite as a geothermometer. The predicted and observed transformation of silica-rich protolith to kaolinite, boehmite, and pyrite underscores the large scale dissolution and removal of silica, with possible implications for the temporal evolution of vent deposits on the lake floor in the Stevenson Island Deep-Hole region.

Effect of nozzle type on fluid flow, solidification, and solute transport in mold with mold electromagnetic stirring

The mathematical model of coupling fluid flow, heat transfer, solidification, solute transport, and the electromagnetic field of the bloom in the upper part of the strand was established with three nozzle types. Then, the flow field, distribution of the temperature, solidification, and macrosegregation of carbon were investigated and compared by numerical modeling. In the case of the straight submerged entry nozzle (SEN), the molten steel flows down deep into the liquid pool, and the depth of the jet flow reaches about 1.0 m beneath the meniscus. The jetting zone is the high-temperature zone. In the case of two-port SEN and four-port SEN, the flow patterns and distribution of temperature in the central longitudinal section are similar. The jet flow impinges directly on the initially solidified shell and then it is divided into two longitudinal circulations. The heat of molten steel is dissipated along with the longitudinal circulations. The negative segregation band was generated near the bloom surface due to the washing effect by the rotating flow at the solidification front with three nozzle types. The negative segregation deteriorates gradually with the number of ports decreasing.