Coupled Computational Fluid Dynamics Research Articles

Development of a dynamic external CFD and BES coupling framework for application of urban neighbourhoods energy modelling

Current building energy models are weak at representing the interactions between neighbourhoods of buildings in cities. The effect of a neighbourhood on the local microclimate is complex, varying from one building to another, meaning that neighbourhood effects on the airflow around a particular building. A failure to account for this may lead to the miss-calculation of heat transfer and energy demand. Current building energy simulation (BES) tools apply convective heat transfer coefficient (CHTC) correlations, which were developed by using a simplified model of wind flow that neglects neighbourhood effects. Computational Fluid Dynamics (CFD) techniques are able to model these neighbourhood effects and can be used to improve CHTC correlations.This work aims to develop a framework that couples CFD and BES tools to enhance the modelling of outdoor convective heat transfer in different urban neighbourhoods. A dynamic external coupling method was used to combine the benefits from both domains. Firstly, a microclimate CFD model was validated before the coupling stage using wind tunnel data. Secondly, the framework was tested using a benchmark model of a building block. Fully converged values of the surface temperature and CHTC were achieved at each time-step by the BES and CFD domains. The results highlight the importance of neighbourhood effect while the prediction of the hourly averaged external convection using coupling method can amend the simulation by up to 64% comparing to the standalone conventional BES models with DOE-2 CHTC approach.

Toward the development of a hydrofoil tailored to passively reduce its lift response to fluid load

The objective of this research is to explore the possibility of using Passive Adaptive Composite (PAC) on structures to help control the lift generated by hydrofoils on boats such as the International Moth. Introducing composite fibres oriented at off-principal axis angles, allow a foil to passively control its pitch angle to reduce the lift generated at higher boat speeds helping to achieve a stable flight in a wide range of weather conditions. PAC utilises the inherent flexibility of a composite structure to induce a twist response under bending load which could be used to minimise the use of active control systems, or even improve the dynamic response of foils in waves. However, to design flexible foils requires numerical and experimental tools to assess the complex fluid structure interactions involved. This paper evaluates a simplified hydrofoil geometry designed to reduce its lift coefficient with increased flow speed. A coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) methodology is presented to predict flexible foil performance. Validation of these numerical tools is achieved through the use of wind tunnel experiments including full field deformation measurements. Twist deformations resulted in a reduction in the effective angle of attack by approximately 30% at higher flow speeds reducing the foil lift and drag significantly.

Development of a numerical approach based on coupled CFD/FEM analysis for virtual fire resistance tests—Part A: Thermal analysis of the gas phase combustion and different test specimens

SummaryIn the present two‐parted study, a numerical approach is shown to consider fire resistance tests in virtual space, including the combustion, thermal analysis of the test specimen, and the deformation process. This part is dealing with the combustion process and thermal analysis of different building materials tested in a fire resistance furnace. Instead of using coupled computational fluid dynamics (CFD)/finite element method simulation for the combustion and thermal heat conduction in the solid, which is commonly used in literature, the present approach considers these transport phenomena in one CFD simulation. This method enables a two‐way coupling between the gas phase and the solid material, where chemical reactions and the release of volatile components into the gas phase can occur (eg, release of water vapour from gypsum). To validate the numerical model, a fire resistance test of a steel door, which is a multilayer construction, and a wall made of gypsum blocks were experimentally and numerically investigated. Due to the chemical reactions inside the gypsum, water vapour is released to the gas phase reducing the flue gas temperature about 80 K. This effect was taken into account using a two‐way coupling in the CFD model, which predicted temperatures in close accordance to the measurement.

Numerical Study of Biomass Grate Boiler with Coupled Time-Dependent Fuel Bed Model and Computational Fluid Dynamics Based Freeboard Model

In this paper, a coupled numerical model is developed to provide an advanced simulation for industrial scale grate boilers. The detailed process of biomass conversion in the grate bed is captured u...

Reduced-order model for robust aeroelastic control

The objective of aeroelastic control, i.e., aeroservoelasticity, is either suppression of instability, such as flutter, or impeding the effect of external excitation, e.g., due to a gust. In the present work, a robust active feedback controller for a NACA64A010 airfoil model under sub- and transonic flow conditions is designed to impede flutter. The airfoilmodel has an elastic heave and pitch suspension and is equipped with an active aerodynamic control surface. The control design is based on linear reduced-order models (ROM) derived from a coupled computational fluid dynamics (CFD)-computational structural mechanics (CSM) simulation environment. Because the control design should be robust across a range of flow conditions, a collection of ROMs, which span the desired operational envelope, is considered. For each condition, the stability region for a three-term controller is determined with a parameter space approach. Building the intersection area for certain flow regimes allows determining the area of robust stability. The possibility of shifting the flutter boundary with a robust controller compared to adaptive control designs is discussed. To determine finally a set of control parameters chosen from within the stabilizing area, an optimization approach is used. Comparisons of the response of the investigated airfoil model under control between ROM and CFD–CSM shows that the linear ROM is able to predict the response very accurately, despite nonlinearities due to shocks in the flow field.

Thermo-structural design of the European DEMO water-cooled blanket with a multiscale-multiphysics framework

The Water-Cooled Lithium-Lead (WCLL) blanket concept is one of four possible embodiments under consideration for the European Demonstration Power Plant DEMO, beyond ITER. It is based on a water-cooled first wall and blanket structure with the RAFMS (Reduced Activation Ferritic/Martensitic Steel, Eurofer 97) as structural material and PbLi as neutron multiplier and tritium breeder. We first develop a multiphysics modeling framework in order to optimize the design and achieve long blanket lifetime, maintainability, and high reliability. The approach is demonstrated by coupling Computational Fluid Dynamics (CFD), heat transfer and solid mechanics. The multiphysics framework is then utilized to provide the loading conditions for a multiscale design approach particularly focused on modeling the effects of both steady-state and operational transients on the structural integrity of the First Wall (FW). The methodology builds on the ITER Structural Design Criteria for In-Vessel Components (ISDC-IC), then extending the criteria to progressively incorporate continuum plasticity models and microstructure-based representation of deformation and fracture. We finally introduce advanced fracture mechanics concepts based on a Materials-Specific Failure Assessment Diagram (MS-FAD), in which precise calculations of the J-integral of an elasto-plastic material is required. This is especially important for the water-cooled design because of the limited fracture toughness of Eurofer 97 below 300 °C. The methodology has been applied to screen the FW/Blanket performance of a range of steady state heat flux assumed to be applied during the plasma pulse flat top, and up to 0.8 MW/m2. It has become clear that the radiation steady state load will be lower than the values screened here, while the local heat flux due to particle loads will lead to global higher values than the values investigated here. The methodology will be further fine-tuned to specific loading conditions in order to assess actual performance limits of the DEMO WCLL BB.

Fluid-structure interaction (FSI) analysis of stent-graft for aortic endovascular aneurysm repair (EVAR): Material and structural considerations

The effect of hemodynamic load on various stent-graft designs used for endovascular aneurysm repair (EVAR) in cardiovascular treatments is studied using a numerical fluid-structure interaction (FSI) analysis that couples computational fluid dynamics (CFD) and finite element analysis (FEA). Radial displacements, mechanical stresses, wall shear stress and wall compliance quantities are evaluated for four stent materials and one graft material. The strut thickness is varied from 0.3 mm to 1 mm. The materials are assumed linearly elastic and isotropic while blood is assumed as a Newtonian and incompressible medium with a pulsatile and turbulent flow profile. Time dependent pressure conditions are assumed at the inlet and outlet. Results are benchmarked against a study taken from the literature and indicate that the stent material and the strut thickness greatly influence the mechanical behavior of the structure. This computational study will serve as an additional tool to vascular surgeons when assessing the choice of material and design for stent-graft recipients.

Toward longitudinal studies of hemodynamically induced vessel wall remodeling.

Autogenous arteriovenous fistula is the preferred vascular access for hemodialysis, but it has high rates of non-maturation and early failure due to vascular stenosis. Convincing evidence supports a key role of local hemodynamics in vascular remodeling, suggesting that unsteady and disturbed flow conditions may be related to stenosis formation in arteriovenous fistula. The purpose of our study was to explore the feasibility of coupling contrast-free magnetic resonance imaging and computational fluid dynamics in longitudinal studies to identify the role of local hemodynamic changes over time in inducing vessel wall remodeling in arteriovenous fistula. We acquired contrast-free magnetic resonance imaging of arm vasculature at 1 week and 6 weeks after arteriovenous fistula creation in a 72-year-old patient. We then generated three-dimensional models and evaluated lumen cross-sectional area of arteriovenous fistula limbs. We performed high-resolution computational fluid dynamics to evaluate changes in local hemodynamics over time. Our contrast-free magnetic resonance imaging protocol provided good quality images in a short scan duration. We observed a homogeneous dilatation in the proximal artery, while there was a more pronounced lumen dilatation in the venous outflow as compared to a limited dilatation in the juxta-anastomotic vein. Furthermore, we observed a slight stabilization of the flow pattern over time, suggesting that vascular outward remodeling accommodates the flow to a more helicoidally phenotype. Coupling contrast-free magnetic resonance imaging and high-resolution computational fluid dynamics represents a promising approach to shed more light in the mechanisms of vascular remodeling and can be used for prospective clinical investigations aimed at identifying critical hemodynamic factors contributing to arteriovenous fistula failure.

Numerical study on extracting energy efficiency by autorotation of elliptic cylinder from low velocity flow

A new concept of power generator using autorotation of elliptic cylinder to extract energy from fluid is proposed in the present study. Numerical simulation studies Fluid-Structure Interaction of the fixed-axis autorotation of rigid elliptic cylinder using a coupled Computational Fluid Dynamics (CFD) – Rigid Body Dynamics (RBD) solver. This solver requires no solid mesh to setup FSI (Fluid Structure Interaction) simulation. Based on solving two-dimensional unsteady incompressible N-S equations and SST k-ω turbulent governing equations, the power generator of elliptic cylinder was investigated in different axis rations, eccentric distance ratios and Reynolds number conditions. Numerical results reveal that autorotation of elliptic cylinder can achieve energy extraction. With optimal parameters, the power generator can reach maximum energy extraction efficiency of 34%. The investigation results provided fundamental support for utilization of ocean current energy.

A Coupled CFD–DEM Simulation of Slurry Infiltration and Filter Cake Formation during Slurry Shield Tunneling

Tunneling in highly permeable ground using a slurry shield machine can be challenging because it is difficult to form the so-called filter cake on the tunnel face to transport the support pressure. Consequently, destructive accidents might happen, such as face instability and water inrush. How to form an efficient filter cake in time is crucial during engineering practice, especially in ground with high permeability. Various theoretical and experimental analyses regarding the formation of filter cakes have been conducted. However, due to the complexity of this problem, which has to incorporate the mechanical and hydraulic behaviors of the fluid–solid mixture system, few numerical simulations are found in the literature. In this paper, with the aid of a newly developed numerical tool, a coupled CFD (computational fluid dynamics)–DEM (discrete element method) simulation is established to study the slurry infiltration and filter cake formation during slurry shield tunneling. The slurry infiltration process is simulated by modelling the scheme of the infiltration column test, in which sedimentation behaviors of slurry particles are captured and compared with experimental results. The results show that the sedimentation behaviors of the slurry particles and filter cake formation phenomenon are well captured by simulations and in accordance with the experiments, which indicates the robustness of the coupled CFD–DEM simulation used in present work.

Crosstalk between IGF2BP RNA-binding proteins and epigenetic regulators in pancreatic neuroendocrine tumors

It is well known that packing non-uniformity may cause peak asymmetry and limit the performance of packed-bed chromatographic columns. However, understanding of the reasons leading to packing non-uniformity is still limited. Therefore, the effect of different column packing methods, i.e. dynamic axial compression (DAC), flow packing, and combinations of both on the hydrodynamic packing heterogeneity and stability of packings composed of polymer-based compressible porous resins with a mean diameter of 90 μm was investigated experimentally as well as in-silico. Deterministic Euler-Lagrange modeling of a small chromatographic column with a diameter of 9.6 mm and a bed height of 30 mm was applied by coupling Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). Interparticle micromechanics as well as the fluid-particle and particle-wall interactions were taken into account. Experiments and simulations revealed substantial non-uniformity of compression force transmission and axial packing density distribution during both dynamic axial compression and flow packing which was related to wall support and interparticle friction. By combining both packing methods sequentially (dynamic axial compression followed by flow packing or vice versa), the compression forces were more homogeneous resulting in improved packing procedures. Repeated alternating application of flow packing and DAC (the so-called hybrid packing method) resulted in the most homogeneous packing density distribution and the highest packing stability which was kept nearly constant during long-term operation with cyclic hydrodynamic load. The hydrodynamic stability of the chromatographic column was evaluated by calculating the integral porosity deviation and packing induced flow velocity dispersion. The hybrid packing method gave the best results for both parameters.

Hydrocarbons for the next generation of jet fuel surrogates

Fuel surrogates are a critical component for the detailed combustion modeling of real transportation fuels. Indeed, the numerical study of engine combustion requires the coupling of computational fluid dynamics and chemical kinetic models, and therefore a limited number of chemical species and reactions can be employed due to current numerical capabilities. As a consequence, surrogates are adopted to simulate the behavior of real fuels. In this study, we evaluate various hydrocarbon molecules that can be employed as next generation surrogate components for conventional and alternative jet fuels. Species considered in this study have smaller number of kinetic data as compared to molecules that are currently used in jet fuel surrogates, but they possess greater physical relevance and the potential to achieve closer emulation of properties when used as jet fuel surrogate components. Using a surrogate optimizer model, we analyze various mixtures that can emulate a petroleum-derived jet fuel (Jet-A POSF-4658) and a coal-derived jet fuel (IPK POSF-5642). The results show that n-tetradecane and n-dodecane are suitable normal alkane representatives for jet fuels. Also, the use of three C9 alkylbenzenes (n-propyl-, 1,2,4-trimethyl-, 1,3,5-trimethyl-benzene) leads to surrogate mixtures with an aromatic content and a distillation curve that matches the experimental values of Jet-A much better than mixtures that contain toluene or C10 alkylbenzenes. In addition, the optimization results with three new branched alkanes for the target IPK show that 2,2,4,6,6-pentamethylheptane is a promising surrogate component for representing low ignition quality highly-branched alkanes in jet fuels. This study highlights the need for experimental studies and further kinetic model development for these molecules, which will benefit the surrogate development for the wide variety of jet fuels in the future.

Development of a Methodology for Interface Boundary Selection in the Multiscale Road Tunnel Fire Simulations

The simulation of large complex dynamical systems such as a fire in road tunnels is necessary but costly. Therefore, there is a crucial need to design efficient models. Coupling of computational fluid dynamics (CFD) models and 1D network modeling simulations of a fire event, a multiscale method, can be a useful tool to increase the computational efficiency while the accuracy of simulations is maintained. The boundary between a CFD model (near field) and a 1D model (far field) plays a key role in the accuracy of simulations of large systems. The research presented in this paper develops a novel methodology to select the interface boundary between the 3D CFD model and a 1D model in the multiscale simulation of vehicle fire events in a tunnel. The development of the methodology is based on the physics of the fluid structure, turbulent kinetic energy of the dynamical system, and the vortex dynamics. The methodology was applied to a tunnel with 73.73 m2 cross section and 960 m in length. Three different vehicle fire scenarios were investigated based on two different heat reslease rates (10 MW and 30 MW) and two different inlet velocities (1.5 m/s and 5 m/s). all parameters upstream and downstream of the fire source in all scenarios were investigated at t = 900 s. The effect of changes in heat release rate (HRR) and air velocity on the selection of an interface boundary was investigated. The ratio between maximum longitudinal and transversal velocities was within a range of 10 to 20 in the quasi-1D region downstream of the fire source. The selected downstream interface boundary was 12Dh m downstream of the fire for the simulations. The upstream interface boundary was selected at 0.5 Dh m upstream the tip of the object when the velocity was greater than equal to the Vc. In the simulations with backlayering (V < Vc), the interface boundary was selected 10 m further from the tip of the backlayering (1.2 Dh). An indirect coupling strategy was utilized to couple CFD models to 1D models at the selected interface boundary; then, the coupled models results were compared to the full CFD model results. The calculated error between CFD and coupled models for mean temperature and velocity at different cross sections were calculated at less than 5%. The findings were used to recommend a modification to the selection of interface boundary in multiscale fire simulations in the road tunnels and more complex geometries such as mines.

CFD–DEM simulation and experimental investigation of the flow behavior of lunar regolith JSC-1A

Rovers on Mars and the Moon analyze the local geology by collecting samples of the upper layer in containers and ovens. After the analysis, the complete discharge of samples from the reservoir must be ensured. Because of the low atmospheric pressure, reduced gravity, and different grain shapes of the bulk material, the discharge process is very different compared to that on Earth. In this study, the behavior of lunar regolith JSC-1A in closed containers during discharge was investigated by analyzing the flow in an hourglass under the Earth’s atmosphere. Reproducible fluidization of the top particle layer was observed during the outflow of the upper half of the hourglass. These particles were fluidized by the displacement flow initiated by falling particles in the completely closed container. This complex problem was simulated by coupling computational fluid dynamics (CFD) with the discrete element method (DEM). A CFD–DEM simulation with 1million particles was performed. Because billions of particles are present in the actual system, the use of a coarse graining approach was required. In addition, high-speed camera measurements were used to determine the velocities of individual particles to validate the simulation. The fluidization effect was successfully simulated using the coupled method.

Multiscale Modeling and Simulation of Macromixing, Micromixing, and Crystal Size Distribution in Radial Mixers/Crystallizers

Continuous-flow tubular crystallization in which seed crystals are continuously generated is of interest due to its enabling of tighter control of crystal properties. This article is the most detailed simulation study on the design and operation of continuous-flow crystallizers using radial mixers, which have potential for inducing rapid and intense turbulent mixing and having easy construction, high reliability, and low operating costs. A multiscale model is employed that couples computational fluid dynamics (CFD), micromixing modeling, energy balance, and population balance equation (PBE) using the open-source CFD package OpenFOAM. The approach is demonstrated for the methanol–water antisolvent crystallization of lovastatin. A new crystallizer design with multiple radial inlets is proposed and shown to deliver improved mixing compared to one radial inlet. The effects of varying operating conditions on micromixing and crystal size distribution are analyzed. A systematic approach is provided for the desig...

Fluid dynamic characterization of a fluidized‐bed perfusion bioreactor with CFD–DEM simulation

AbstractBACKGROUNDIn the recent development of regenerative medicine, the low yields of progenitor cells have limited the large‐scale clinical applications. To overcome the limitation, a novel fluidized bed bioreactor has emerged. However, a detailed understanding of its fluid dynamics is still lacking.RESULTSA 3D modeling approach that couples computational fluid dynamics (CFD) and a discrete element method (DEM) was used to simulate the liquid and solid flows in a bioreactor being designed for stem cells expansion. The model was validated by comparing the simulation results with literature experimental data [Chem Eng Sci 60:1889–1900 (2005)], which showed a good agreement. Using the validated model, the effects of the superficial liquid velocity, particle size and particle density on the solids volume fraction, shear stress on the particles and liquid–solid mass transfer coefficient of dissolved oxygen and glucose were analyzed.CONCLUSIONSSimulation results show that particle size and density have an important impact on the shear stress distribution, and that the liquid velocity affects the shear stress distribution rather modestly when its value is beyond the minimum fluidization velocity. The liquid–particle mass transfer coefficient of dissolved oxygen and glucose can be improved by raising the liquid velocity, and the adoption of a high‐density material allows the reactor to operate with higher liquid velocities before reaching shear stress heterogeneities. Furthermore, the two objectives, (i) maintaining lower and homogeneously distributed shear stress and (ii) improving mass transfer, pose conflicting requirements on certain design parameters which need to be carefully considered in the reactor design. © 2018 Society of Chemical Industry

Transient CFD/Monte-Carlo Neutron Transport Coupling Scheme for simulation of a control rod extraction in TRIGA reactor

The computational model of the JSI TRIGA Mark II, coupling Monte-Carlo neutron transport code TRIPOLI and computational fluid dynamics code CFX was used to reproduce the behaviour of the reactor after extraction of a control rod. To tackle the time dependent Boltzmann equation, a quasistatic approach has been used and compared with point kinetic. Qualitative assessment of the model was performed by comparison with measured fuel temperature and power. Time evolutions of power and fuel temperature were reproduced. The quasistatic approximation was justified by updating the shape function at different time intervals. The quasistatic approach successfully reproduces the experimental results obtained with the TRIGA reactor. It was shown that most of the local effects (temperature, power density) were due to the control rod and that local effects of coupling were small.

Simulating the human body's microclimate using automatic coupling of CFD and an advanced thermoregulation model.

This study aims to develop an approach to couple a computational fluid dynamics (CFD) solver to the University of California, Berkeley (UCB) thermal comfort model to accurately evaluate thermal comfort. The coupling was made using an iterative JavaScript to automatically transfer data for each individual segment of the human body back and forth between the CFD solver and the UCB model until reaching convergence defined by a stopping criterion. The location from which data are transferred to the UCB model was determined using a new approach based on the temperature difference between subsequent points on the temperature profile curve in the vicinity of the body surface. This approach was used because the microclimate surrounding the human body differs in thickness depending on the body segment and the surrounding environment. To accurately simulate the thermal environment, the numerical model was validated beforehand using experimental data collected in a climate chamber equipped with a thermal manikin. Furthermore, an example of the practical implementations of this coupling is reported in this paper through radiant floor cooling simulation cases, in which overall and local thermal sensation and comfort were investigated using the coupled UCB model.

A coupled CFD-PBM and thermodynamic analysis of continuous supercritical hydrothermal synthesis of nanoparticles

The coupled Computational Fluid Dynamics (CFD)-Population Balance Model (PBM) and the Gibbs-energy minimization based thermodynamic model are presented for the continuous supercritical hydrothermal synthesis of nanopartices. The coupled model is tested with published experimental data of ceria nanoparticle synthesis. Three different flow configurations of the T-mixer are evaluated based on the mixing index, an average temperature of the mixture, product particle size distribution (PSD), and time scales for various stages of nanoparticle production. The product PSD is broader, when back-mixing is dominant, whereas it is narrower when mixing is limited over a small volume. Time scale analysis reveals that the overall synthesis process can be either reaction controlled or mixing controlled based on the flow configuration and operating conditions. Further, scaling relationships between an average particle size and the process conditions are derived for three flow configurations, which are useful for design and optimization of the hydrothermal process for nanoparticle production.

Application of a multi-variable optimization method to determine lift-up design for optimum wind comfort

The lift-up building design has been demonstrated to provide favorable wind comfort, but there is a lack of investigation on optimum wind comfort condition. This study coupled computational fluid dynamics (CFD) technique and response surface methodology (RSM) to determine the most desirable wind comfort around an isolated building with lift-up design. A multi-variable optimization method is proposed to determine optimum wind comfort and the corresponding lift-up design variables, namely, lift-up height (HL), core aspect ratio (AR) and core number (N). To better illustrate wind comfort around the building, the wind comfort in the lift-up area and the podium area are investigated separately. The Detached Eddy Simulation (DES) approach is employed throughout the whole CFD simulation process. The quality and goodness of the established RSM models are examined by analysis of variance and genetic algorithm is applied to generate optimal design solution. The generated results illustrate good performance of the established RSM model. Results show that the optimum wind comfort is obtained when HL is 8 m, AR is 10%, and N is 6. The lift-up core aspect ratio is subsequently found to have greatest effect on wind comfort among the three design variables in both the lift-up area and the podium area. In addition, the proposed method is applicable to other similar environmental design conditions and the outcomes of study can also be of great value in the improvement of wind comfort in compact urban cities.