Coupled Computational Fluid Dynamics Research Articles

Accessing multidimensional mixing via 3D printing and showerhead micromixer design

AbstractWe present a 3D metal printing showerhead mixer to blend effectively two reagent streams into a confined mixing volume. Each stream is predistributed to multiple channels to increase the contact area in the mixing zone, which enables high mixing performance with smaller pressure drop. The showerhead mixer shows excellent mixing performance owing to its ability to intersperse rapidly the two streams as characterized by the diazo coupling reactions and computational fluid dynamics (CFD) simulations. Experimental results demonstrate superior performance of the showerhead mixer compared to two common commercial micro T‐mixers, especially in low Reynolds number regime. CFD results are employed to (a) help understand the mixing mechanism, (b) reproduce the experimental observations, and (c) inform the design specifications for optimal performance. Good agreement between experiments and simulations is achieved. The final design includes multiple side‐fed inlets for improved mixing performance of the showerhead mixer, as suggested by the validated CFD models.

Coupled CFD and particle resuspension models under combined effect of mechanical and aerodynamic disturbances

Particle resuspension in indoor spaces constitutes a concern to human health as it re-introduces deposited particles on surfaces into the bulk air. Resuspension can occur due to indoor human activities causing aerodynamic and mechanical vibration disturbances. The objective of the work is to develop a simplified model that can predict resuspension triggered by the simultaneous action of aerodynamics and vibration forces from hard floor material. The mathematical model was coupled with computational fluid dynamics (CFD) model to predict, through a probabilistic approach, the rates of particle resuspension from indoor surfaces due to indoor activities. The developed model accounted for the reduction of adhesive forces due to vibrations and for the lift and drag forces and moments due to the fluid flow while setting the resuspension condition to predict the resuspension rates. The resuspension model was validated by published literature data on particle resuspension due aerodynamic and mechanical disturbances and good agreement was found. Resultsshowed that particle resuspension exhibited a rapid burst during the first 25 s of the disturbance before decreasing to negligible values. Resuspension rates also increased when vibrations were accounted for with aerodynamic disturbances. For different indoor surfaces, it was found that resuspension fractions were the smallest for glass surfaces, followed by marble and linoleum. Moreover, resuspension fractions increased by 48.4%, 60.5% and 63% for glass, marble and linoleum when aerodynamic disturbances were accompanied with vibrations. A decrease in surface roughness can increase adhesive forces, and stiffness values reducing the effect of vibrations on enhancing resuspension.

Noise reduction of flow MRI measurements using a lattice Boltzmann based topology optimisation approach

In a previous work, the feasibility of coupling magnetic resonance imaging (MRI) measurements and computational fluid dynamics (CFD) was presented, called CFD-MRI. Using a lattice Boltzmann based topology optimisation approach, the method can be described as a Navier–Stokes filter for flow MRI measurements. The main objective of this article is the analysis and quantification of CFD-MRI for its ability to reduce statistical measurement noise. For this, MRI data was analysed and used as basis for synthetic data, where noise was added to a simulation result. Thus, the noise-free data is known and a thorough analysis can be performed. The results show a very high agreement with the original data, even with high statistical noise in the input data and limited information available.

A Novel, Coupled CFD-DEM Model for the Flow Characteristics of Particles Inside a Pipe

This study developed a novel, 3D coupled computational fluid dynamics (CFD)-discrete element method (DEM) model by coupling two software programs, OpenFOAM and PFC3D, to solve problems related to fluid–particle interaction systems. The complete governing equations and the flow chart of the coupling calculations are clearly presented herein. The coupled CFD-DEM model was first benchmarked using two classic geo-mechanics problems, for which the analytical solutions are available. Then, the CFD-DEM model was employed to investigate the flow characteristics of a particle heap subjected to the effects of water inside a pipe under different conditions. The results showed that particle size and pipe inclination angle can significantly affect the particle flow morphology, total kinetic energy and erosion rate for mono-sized particles, whereas polydisperse particles had a slight effect. This model can accurately describe the flow characteristics of particles inside a pipe, and the results of this study were consistent with those of previous studies. The reliability of this model was further demonstrated, which showed that this model can provide valuable references for solving similar problems such as soil erosion and bridge scour problems.

Numerical investigation of a double-circulation system for cuttings transport in CBM well drilling using a CFD-DEM coupled model

ABSTRACT In this study, a numerical model of a partial wellbore is developed by coupling computational fluid dynamics (CFD) with the discrete element method (DEM) in order to simulate the operation of a double-circulation system (DCS) in coalbed methane (CBM) well drilling, which is a novel technique used for cuttings transport. The values of the flow field are computed by a fluid solver and the motions of the particle phase are calculated by the DEM, for which an additional multi-sphere particle model is integrated. After verification of the model, the analysis centers on the working mechanism, the DCS parameters, and optimization of the angle θ of the injection nozzles, which is the most critical parameter affecting the efficiency of the DCS. Simulations reveal the working details of the DCS and prove its applicability to cuttings transport, especially in the curved and horizontal parts of the well. The effects of viscosity and particle size are investigated, and a low-viscosity drilling fluid is recommended. The optimal range for θ is obtained as 30° to 50°. This work provides a reference for the engineering application of DCSs, and by feedback from drilling sites the reliability of the results can be verified.

Best practices for modeling structural boundary conditions due to a localized fire

SummaryRecent studies suggest the assumption of uniform heating that is used in current structural fire design cannot be assumed conservative, especially if the fire is expected to burn locally. Aside from design equations, which have limited applicability, a common approach to simulating structural members subjected to a localized fire is modeling the fire‐structure interaction using a coupled computational fluid dynamics (CFD)‐finite element (FE) model. In the existing literature, a wide range of methods and parameters are used when determining the boundary conditions at the fire‐structure interface, specifically regarding the representation of net heat flux, heat transfer coefficient, and surface emissivity of steel. The purpose of this study is to investigate various methods for representing the boundary conditions in terms of accuracy and computational efficiency and then identify best practices. In conclusion, our study found that net heat flux predicted by adiabatic surface temperature, a nonconstant heat transfer coefficient, and a surface emissivity of 0.9 for steel was the most reliable thermal boundary condition in a coupled CFD‐FE model of a localized fire. These recommendations are based on the two cases studied here, and caution should be used when applying these results to future studies.

Coupled numerical simulations of cooling potential due to evaporation in a street canyon and an urban public square

The extent and duration of evaporative cooling, as a countermeasure to the urban heat island effect, depend on factors such as moisture availability and material liquid capacity and permeability. The present study investigates the evaporative-cooling potential of conventional urban materials and green surfaces using two case studies: an isolated street canyon and a historical public square in the city of Zurich with a particular focus on pedestrian thermal comfort. The numerical model couples computational fluid dynamics (CFD) simulations of wind flow with the heat and moisture transport (HAM) in urban materials in order to resolve storage and transport in urban settings. This way, we aim to provide a framework for the development of sustainable and resilient solutions for local heat islands.

Effect of particle size and concentration on the migration behavior in porous media by coupling computational fluid dynamics and discrete element method

Particle migration and the deposition process in porous media have received wide attention, especially in petroleum and chemical industries. Several studies have been conducted to address this issue, however, the mechanism is still ambiguous. Here we investigate the process of particle migration in porous media by coupling computational fluid dynamics and discrete element method. The classical Ergun equation and the DKT phenomenon were employed to validate our program. During the migration process, we observed that owing to the effect of particle exclusion and bridging, the behavior of suspended particles is primarily controlled by particle size. Particles will occupy the pore space and reduce the permeability of porous media gradually when the particle concentration increases. However, as the external filtration cake grows the permeability tends to be insensitive to particle concentrations. It also suggests the existence of the critical particle size which results in a remarkable decrease of permeability. Keywords: porous media; particle migration, computational fluid dynamics, discrete element method, fluid flow.

Multi-Scale Multi-Field Coupled Analysis of Power Battery Pack Based on Heat Pipe Cooling

Based on the study of the relationship between micro and macro parameters in the actual microstructure of the electrodes, a new multi-scale multi-field coupling model of battery monomer is established and the heat generation rate of the battery is obtained by detailed numerical simulation. According to the parameters of a certain electric vehicle and battery selected, the structure of the power battery pack and heat pipe cooling system is designed. Through multi-field coupling computational fluid dynamics simulation, the temperature difference of the battery pack is gained. By changing the fin spacing, the cooling scheme of the heat pipe is optimized, which ensures that the temperature difference is less than 5 K and the maximum temperature of the battery system is 306.26 K. It is found that increasing the discharge rate, the temperature difference increases rapidly. Increasing the air inlet velocity can improve the thermal uniformity of the battery pack, but changing the air inlet temperature only determines the range of temperature, it cannot improve the thermal uniformity. The method proposed and results gained can provide a reference for the research of heat management systems with heat pipe of lithium-ion power battery pack for vehicles.

Coupled CFD-DEM analysis of parameters on bridging in the fracture during lost circulation

As an important preventive and remedial application of lost circulation, the optimization of lost circulation materials (LCMs) has become a crucial problem. In order to optimize the design of LCMs, the mechanism of bridging was studied. Based on the theory of solid-liquid flow, a coupled Computational Fluid Dynamics (CFD) - Discrete Element Method (DEM) model was introduced to accurately simulate the dynamic bridging process of plugging particles. The criterion of critical bridging concentration was developed to quantitatively evaluate the effects of Young's modulus, particle density, particle size distribution (PSD), friction coefficient, fracture geometry, lost circulation velocity and fluid yield stress on bridging capacity. The results show that the plugging zone will become more stable with the increase of particle angularity, Young's modulus, density of LCMs, lost circulation velocity and the decrease of fluid yield stress. The friction failure is easier to occur, because the stability of plugging zone is more sensitive to the friction between particle and fracture surface. The critical bridging concentration is more sensitive to the ratio of inlet size to outlet size (Rio) with a higher ratio of outlet size to particle size (Ro). For a small outlet size (Ro ≤ 2.5), the bridging state can be observed obviously because the large particles are dominant. When the outlet size is larger (Ro > 3), the stable plugging zone is hard to form because the dense state increases the risk of friction failure. The hindering effect of gravity on the trajectory of particles will be more significant when the fracture extension direction is perpendicular to the gravity direction.

Thermal flutter prediction at trajectory points of a hypersonic vehicle based on aerothermal synchronization algorithm

Abstract Due to orders of magnitude differences in time scale between structural heat transfer and aeroelastic responses, one-way aerothermal-aeroelastic coupling is adopted to develop a thermal flutter prediction method for a hypersonic vehicle operating along a desired trajectory. In view of the strong dependency of the heat transfer process on the unsteady hypersonic trajectory, an aerothermal synchronization algorithm is established in a non-inertial frame of reference by formulating the governing equations of fluid flow and heat transfer into a unified form. Then the heated free-vibration frequencies and mode shapes are calculated at each trajectory point by using a finite-element analysis. Consequently, the flutter computations are performed on the transiently heated structure at each trajectory point by utilizing a coupled computational fluid dynamics (CFD)/computational structural dynamics (CSD) method. Because of the mass dissimilarity caused by directly increasing the dynamic pressure of a compressible flow, the technique of variable stiffness is introduced to evaluate the flutter dynamic pressure at the point of mass similarity and the stiffness margin of flutter. The present method is applied to the thermal flutter computations of a hypersonic all-movable rudder operating along a given trajectory. The computed temperature differences between the synchronization and conventional partitioned methods, and the significant effects of aerodynamic heating on the structural modes and the flutter characteristics are analyzed in detail.

Accelerated heat transfer simulations using coupled DEM and CFD

This work presents an accelerated simulation of heat and mass transfer by coupling Discrete Element Methodologies (DEMs) and Computational Fluid Dynamics (CFD), utilising Graphics Processing Unit (GPU) technology. The presented model is a continuation of previous work from Hobbs (2009) [1] and focuses on demonstrating the capabilities and effectiveness of implementing the GPU combined with the Central Processing Unit (CPUs) technologies to run a complex industrial simulation. Furthermore, different flighting configurations have been used to investigate the influence of the design to the drying process. A model of an aggregate drum dryer was used to produce hot mix asphalt and different computing configurations have been implemented to investigate the effect of GPU-CPU technology in such a complex simulation. Commercial codes from ANSYS and DEM Solutions were coupled to simulate heat transfer from the hot gases to the aggregate particles. Fluid flow and particle-fluid interactions are solved by the CFD solver which exchanges information at regular intervals. The results showed that the coupled model captures accurately the convective heat transfer from the fluid to the solid phase and demonstrated significant improvement in terms of simulation time. The proposed model has significant impact in industrial applications as it provides insight on how to simulate large-scale applications rapidly and accurately.

Coupled unsteady computational fluid dynamics with heat and mass transfer analysis of a solar/heat-powered adsorption cooling system for use in buildings

In recent years, considerable interest has been given to the application of solar-powered cooling technology for use in buildings. Solar cooling systems look like to be a suitable substitution to the traditional vapour-compression electrical-driven machines. Solar systems have the advantage of using harmless working fluids, especially water. They also have the capacity to decrease the peak loads for electricity utilities and can contribute to a substantial reduction of the harmful CO2 emissions, which produce the notorious greenhouse effect that in turn is responsible for global warming and its devastating consequences. Amongst cooling technologies, low-temperature, solar-powered adsorption chillers/heat pumps are arising as a sustainable alternative to electrical vapour-compression systems.This study aims at examining the impact of design and operating factors on an adsorption cooling system’s performance in a residential application. An unsteady Computational Fluid Dynamics (CFD) combined with a heat and mass transfer model of the adsorption cooling system using adsorbent/water pair, was created in order to predict the following: (1) Flow behaviour; (2) Pressure; (3) Temperature; and (4) Water adsorption distributions. For possible adsorbents, both silica gel and zeolite 13X were considered; however, it is worth mentioning that silica gel was used at a lower working temperature range, as required by the operation. This makes silica gel an efficient option for solar/heat driven residential cooling applications. For the CFD model implemented equations, two geometries found in literature were employed for validation. Validation of the unsteady simulation results with experimental data found in literature showed favourable agreements. In a parametric study, various computation cases underwent simulation over the duration of the adsorption mode, which considered the following set of factors: heat transfer fluid (HTF) velocity (v); adsorbent bed thickness (lbed); heat exchanger tube thickness (b); and adsorbent particle diameter (dp) in order to perform a detailed investigation for main geometrical and operating parameters’ influence upon system performance. Results obtained from CFD disclosed the significance of v, lbed and dp whereas b was found having relatively minor modifications within the system performance. Additionally, the development of CFD combined with heat and mass transfer model serves as an effective tool for both simulation and optimisation of adsorption cooling systems as well as for performance predicting purposes.

Structural signature of binary sphere mixtures under air impact

Packings of binary spheres formed under air impact were simulated using the coupled computational fluid dynamics (CFD) and discrete element method (DEM) approach. The effects of particle size ratio (PSR) on structural properties of the packings before and after air impact were analysed. The results showed that the air impact condensed the packings. The second peak in the RDF curves became more apparent and the third peak gradually disappeared in the final packings with increasing PSR. The number of contacts between large spheres decreased, while the contacts between large and small spheres increased under the effect of air impact. The orientation of the contacts tended to be more directional for the final packings. Radical tessellation analyses indicated that for both initial and final packings, two peaks were always formed in the distributions of face number per cell, face area and relative volume, while only one peak appeared in the distributions of edge number and perimeter. Furthermore, the average metrical properties for large particles hardly changed with PSR in the final packings, while those for small or all particles decreased after air impact.

Analysis of Pollutant Dispersion in a Realistic Urban Street Canyon Using Coupled CFD and Chemical Reaction Modeling

Studies in actual urban settings that integrate chemical reaction modeling, radiation, and particular emissions are mandatory to evaluate the effects of traffic-related air pollution on street canyons. In this paper, airflow patterns and reactive pollutant behavior for over 24 h, in a realistic urban canyon in Osaka City, Japan, was conducted using a computational fluid dynamics (CFD) model coupled with a chemical reaction model (CBM-IV). The boundary conditions for the CFD model were obtained from mesoscale meteorological and air quality models. Inherent street canyon processes, such as ground and wall radiation, were evaluated using a surface energy budget model of the ground and a building envelope model, respectively. The CFD-coupled chemical reaction model surpassed the mesoscale models in describing the NO, NO2, and O3 transport process, representing pollutants concentrations more accurately within the street canyon since the latter cannot capture the local phenomena because of coarse grid resolution. This work showed that the concentration of pollutants in the urban canyon is heavily reliant on roadside emissions and airflow patterns, which, in turn, is strongly affected by the heterogeneity of the urban layout. The CFD-coupled chemical reaction model characterized better the complex three-dimensional site and hour-dependent dispersion of contaminants within an urban canyon.

Predicting the performance of pressure filtration processes by coupling computational fluid dynamics and discrete element methods

To obtain a fundamental understanding of the various factors affecting pressure filtration performance, we developed a coupled computational fluid dynamics (CFD) and discrete element method (DEM) model for simulating the effect of solvent flow through the solid particle cake. The model was validated using data collected by filtering mixtures of spherical glass beads and deionized water through a dead-end cell over a range of applied pressures. Numerical experiments were performed to study the effects of particle properties, liquid properties and operating conditions on filtration performance. The model predicted that the filtrate flow rate could be strongly affected by the mean size of the particles, the presence of small particles (i.e. fines) in the particle distribution, the viscosity of the liquid, and particle deformation leading to cake compression. Our study demonstrated that CFD-DEM modeling is a powerful approach for understanding cake filtration processes and predicting filtration performance.

Influence of particle shape on microstructure and heat transfer characteristics in blast furnace raceway with CFD-DEM approach

Coupled computational fluid dynamics and discrete element method (CFD-DEM) simulations are conducted to investigate the influence of particle shape on microstructure and heat transfer characteristics in a blast furnace (BF) raceway. Spherical and non-spherical particles including tetrahedron-like and octahedron-like shapes are involved in this work. The applicability of the coupled approach and the accuracy of combined sphere method (CSM) to investigate the kinetic and thermodynamic behaviors are validated firstly based on the experimental results. Then, the influences of particle shape on raceway formation, microstructure, and particle temperature evolution are comprehensively explored. The numerical results show that the tetrahedron-like particle system presents a relatively stronger interlocking efficiency and thus leads to a smaller raceway size. Additionally, the non-uniform performance of temperature in this system is more striking than the other two cases. However, the bigger raceway size exists in the octahedron-like particle system and the average particle temperature is also higher than other cases; meanwhile, this system possesses more powerful rotational kinetic energy but lower drag force required to form and maintain the raceway than tetrahedron-like system under the same inlet velocity. These findings could be beneficial for the in-depth understanding of microstructure and heat transfer characteristics within a BF raceway.

Modelling of reactor pressure vessel subjected to pressurized thermal shock using 3D-XFEM

We describe the model developed for integrity assessment of a reactor pressure vessel (RPV) subjected to pressurized thermal shock (PTS). The assessment is based on a multi-step simulation scheme, which includes the thermo-hydraulic, thermo-mechanical and fracture mechanics analyses. The thermo-mechanical model uses the three-dimensional finite element method (FEM) to calculate the stress fields of the reactor pressure vessel (RPV) subjected to the thermal load and pressure during large break loss of coolant accident (LBLOCA). In this contribution, the multistep simulation scheme is extended to the analysis of two-phase steam-water flow occurring in the LBLOCA situation and the fracture analysis of postulated cracks under this accident event. It is demonstrated that the principle of the combined one-way coupled system code, CFD and structural mechanics codes can be used for the fracture analysis in case of a transient accident, which involves two-phase flow. The prediction of the temperature field is achieved by using two-phase computational fluid dynamics (CFD) simulation. To perform the stress analysis, an appropriate finite element discretization of the RPV wall is used, which considered the cladding and the ferritic low allow steel. The calculation of the stress intensity factor (SIF) in mode I for hypothetical cracks located in critical positions of the RPV is based on the linear elastic fracture mechanics (LEFM).The fracture mechanics model is based on the node-based submodeling technique in combination with XFEM in Abaqus. This is used to refine the mesh required by the fracture analysis in the region of interest, especially those regions under the cooling plume formed during the LBLOCA. The submodel may contain three types of cracks: axial, circumferential and inclined. The performed integrity assessment compares the stress intensity factor calculated in the deepest point of a surface crack with the material’s fracture toughness. Two approaches to extract the stress intensity factor were applied in the present paper, namely, the classical FEM and eXtended FEM or XFEM. The classical FEM and XFEM solutions are compared. Both techniques give similar results. However, XFEM is more convenient as it is mesh independent.

Efficient FORM-based extreme value prediction of nonlinear ship loads with an application of reduced-order model for coupled CFD and FEA

In this paper, a method for predicting the extreme value distribution of the vertical bending moment (VBM) in a ship under a given short-term sea state is presented. To predict the extreme value distribution of the VBM, the first-order reliability method (FORM), by which the most probable wave episodes (MPWEs) leading to given VBMs are identified, is introduced. The coupled computational fluid dynamics (CFD) and finite-element analysis (FEA) are used to provide the high-fidelity numerical solutions for the wave-induced and whipping components of the VBM. Then, a Reduced-Order Model (ROM) which can yield the predictions equivalent to the coupled CFD–FEA results in a relatively short time is developed. The ROM is incorporated into FORM to identify the MPWEs, in lieu of the coupled CFD–FEA. The accuracy of the ROM is verified by comparing with the coupled CFD–FEA results under identified MPWEs, in terms of both the wave-induced and whipping VBM. Then, a series of tank tests using a scaled container ship is conducted. In the first series of the tests, the VBM measurements under the MPWEs identified from the FORM-based approach using the ROM are made, to validate the accuracy of the ROM. The extreme value distribution of the combined wave-induced and whipping VBM is also measured by performing the second series of the tests, in random waves. The validity of the FORM-based extreme value prediction using the ROM is investigated by comparing with the second series of the tests.

Numerical investigation into combined global and local hydroelastic response in a large container ship based on two-way coupled CFD and FEA

In this study, for efficient safety assessment of a ship’s hull girder subjected to a combination of the global vertical bending moment (VBM) and the local double-bottom bending moment (DBM), a numerical method based on a coupled computational fluid dynamics (CFD) and finite-element analysis (FEA) is first developed. The mutual two-way coupled CFD and FEA in which the elastic deformation of the ship is taken over to the CFD solutions is employed. The present two-way coupled method is developed in two steps, in a weakly coupled manner and a strongly coupled manner. The developed two-way coupled methods are validated via a comparative study against the available experimental results and the straightforward one-way coupled CFD and FEA in terms of the rigid body motion, VBM, and local water pressure. Using the present strongly coupled method, the added mass with regards to the elastic deformation of the ship is reflected in the results of a decrease in the frequency of 2-node vibration mode of the ship or the vibratory (hydroelastic) component in the water pressure. Then, the DBM is evaluated using the estimated water pressure on the ship bottom. An investigation is finally made into the effect of the hydroelastic component in the DBM on the total DBM and the hull girder ultimate strength.