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Quantitative assessment of the complex hemodynamic environment in type B aortic dissection (TBAD) through computational fluid dynamics (CFD) simulations can provide detailed insights into the disease and its progression. As imaging and computational technologies have advanced, methodologies have been developed to increase the accuracy and physiological relevance of CFD simulations. This study presents a patient-specific workflow to simulate blood flow in TBAD, utilising the maximum amount of in vivo data available in the form of CT images, 4D-flow MRI and invasive Doppler-wire pressure measurements, to implement the recommended current best practice methodologies in terms of patient-specific geometry and boundary conditions. The study aimed to evaluate and verify this workflow through detailed qualitative and quantitative comparisons of the CFD and in vivo data. Based on data acquired from five TBAD patients, a range of essential model inputs was obtained, including inlet flow waveforms and 3-element Windkessel model parameters, which can be utilised in further studies where in vivo flow data is not available. Local and global analysis showed good consistency between CFD results and 4D-MRI data, with the maximum velocity in the primary entry tear differing by up to 0.3 m/s, and 80% of the analysed regions achieving moderate or strong correlations between the predicted and in vivo velocities. CFD predicted pressures were generally well matched to the Doppler-wire measurements, with some deviation in peak systolic values. Overall, this study presents a validated comprehensive workflow with extensive data for CFD simulation of TBAD.

A theoretical fluid mechanical model is proposed for the investigation of myocardial perfusion in healthy and stenotic conditions. The model hinges on Terzaghi’s consolidation theory and reformulates the related unsteady flow equation for the simulation of the swelling–drainage alternation characterizing the diastolic–systolic phases. When compared with the outcome of experimental in vivo observations in terms of left ventricle transmural perfusion ratio (T.P.R.), the analytical solution provided by the present study for the time-dependent blood pressure and flow rate across the ventricle wall proves to consistently reproduce the basic mechanisms of both healthy and ischemic perfusion. Therefore, it could constitute a useful interpretative support to improve the comprehension of the basic hemodynamic mechanisms leading to the most common cardiac diseases. Additionally, it could represent the mathematical basis for the application of inverse methods aimed at estimating the characteristic parameters of ischemic perfusion (i.e., location and severity of coronary stenoses) via downstream ventricular measurements, possibly inspiring their assessment via non-invasive myocardial imaging techniques.

UASB reactors are a promising option for environmentally friendly wastewater treatment due to their reduced carbon footprint and their capacity to treat a variety of wastewater strengths, among other recognized advantages over alternative wastewater treatment systems. The Influent Distribution System (IDS) is a critical structure for generating granules in a UASB reactor since it provides the required flow hydrodynamics for their formation. Thus, the objective of this study was to evaluate and compare the efficiency of five IDS configurations to generate ideal granulation conditions using Computational Fluid Dynamics (CFD) simulations. The IDS configurations were as follows: (C1) single radial inflow, (C2) upward axial inflow, (C3) downward distributed axial inflow, and two novel configurations in the form of (C4) double opposite radial inflow and (C5) downward tangential inflow. The hydrodynamic response of configuration C1 was validated in a physical model with dynamic Froude similitude. The granulation measurement was velocity-based in the reactor reaction zone using steady-state CFD simulations. The novel IDS configuration C4 was the one that resulted in the highest granulation volume, with up to 45.5% of the potential granulation volume of the UASB reactor, in contrast to the IDS C2 that obtained the lowest granulation with only 10.8%. Results confirm that the IDS directly impacts the hydrodynamics of the reactor and that model-based design can be used to ascertain IDS configurations that better promote granulation in UASB reactors.

The efficiency of ejector-based systems (the “system-scale”) relies on the behaviour of the ejector (the “component-scale”), related to the flow phenomena within the component itself (the “local-scale”). As a consequence of this multi-scale connection, the precise prediction of the “local-scale” is of fundamental importance to sustain the design of commercially viable ejector-based systems. Although it is widely accepted that computational fluid-dynamics can achieve the prediction of the “local-scale” (CFD) modelling approaches, a broad agreement regarding the performances of numerical methods is not reached: different authors applied different methods, and a complete validation is missing so far. This paper contributes to the current discussion and closes the knowledge gap by assessing the performances of a CFD approach for single-phase supersonic ejectors. To this end, a comprehensive validation has been conducted, encompassing a wide range of ejector designs, boundary conditions and working fluids; besides, a screening of modelling approaches is conducted, encompassing a wide range of mesh criteria, geometrical modelling (2-Dimensional and 3-Dimensional approaches), solvers (density-based and pressure-based) and turbulence models (k-e RNG and k-ω SST). The extensive comparison with experimental data allowed assessing and determining the influence of mesh criteria, geometrical modelling, solvers and turbulence models. In particular, k-ω SST has shown the best agreement with the experimental measurements concerning both global and local flow quantities, with an average entrainment ratio error of 14% and a maximum of 20%, under on-design operating mode. Finally, the simulation outcomes have been further post-processed to derive ejector component efficiencies, to contribute to the present discussion regarding closures in lumped parameter ejector modelling approaches. In conclusion, this paper thoroughly assesses the performance of a CFD model for single-phase ejector simulations and poses precise guidelines to be applied in future research activities and to support the design of ejector-based systems.

Food process modeling has matured with the development of multiscale, multiphase and multi-physics approaches. More comprehensive numerical tools and software platforms for improving insights and optimizing designs and processes have emerged. In the context of industrial digitalization and the advent of the Internet of Things, the concept of the digital twin has recently emerged as a means for more versatile process operational management. The digital twin is defined as a virtual replica of the real process operation, which is connected to the real world by sensor data and advanced big data analytical tools. While all elements are available for implementing digital twins, with the different types of models playing a central role, it will require a multidisciplinary approach for successful implementation and operation. The first agrofood applications still need to be demonstrated. This paper mainly focusses on the role more physics-based models can play, in addition to data-driven and hybrid models.

This novel face mask is designed to be a reusable respirator with a small and highly efficient disposable fabric filter. Respirator material requirements are reduced by 75% compared to traditional designs and allow repeated cleaning or sterilization. The probability of virus particle inhalation is reduced using novel air filtration pathways, through square-waveform design to increase filter airflow. Air enters the mask from right and left side filters, while the area in front of the mouth is isolated. Clear epoxy is used for a transparent frame, allowing lip-reading, and mask edges contain a silicone seal preventing bypass of the filters. The mask is manufactured using silicone molds, eliminating electricity requirements making it economical and viable in developing countries. Computational fluid dynamics numerical studies and Fluent ANSYS software were used to simulate airflow through the filter to optimize filter air path geometry and validate mask design with realistic human requirements. The breathing cycle was represented as a transient function, and N95 filter specifications were selected as a porous medium. The novel design achieved 1.2 × 10−3 kg s−1, 20% higher than human requirements, with air streamlines velocity indicating local high speed, forcing and trapping virus particles against filter walls through centrifugal forces.

The accuracy and reliability of 3D steady RANS CFD simulations of wind flow in urban environments can be affected by numerical settings including the turbulence model and the imposed roughness heights. In that regard, various k-ε and k-ω turbulence models and roughness height (ks) values are commonly used when predicting wind flow in urban environments. However, it is insufficiently known to which extent the CFD results may be influenced by these settings when simulating wind flows in complex urban environments with large changes in surface roughness. This is the scope of the present paper, for which wind-tunnel (WT) measurements and CFD simulations were performed on a reduced-scale model (1:300) of a district of Livorno (Italy). Mean wind speed (U), turbulent kinetic energy (k) and turbulence dissipation rate (ε) profiles from WT measurements and CFD simulations were compared at 25 positions and deviations between experimental and numerical results were quantified by three metrics: fractional bias, correlation coefficient and fraction of data within a factor of 1.3. The turbulence model selection had a larger impact compared to the surface roughness selection on U, k and ε values. The best and worst performing turbulence models (e.g. for α = 240° at 0.02 m above the bottom) showed a deviation in terms of correlation (0.89 and 0.61, respectively) of about 0.28. Conversely, the best and worst performing roughness set, (e.g. for α = 240° at 0.02 m above the bottom), showed a deviation in terms of correlation (0.77 and 0.78, respectively) of only 0.01.

The use of small hydrocyclones for the separation of particles in the micron range is of growing interest. However, these hydrocyclones are typically limited to conventional shapes or restricted to specific outlet sizes, which can lead to sub-optimal performance. The aim of this study is to present a method for the optimisation of small hydrocyclone design. This method consists of four steps that combine designing, Computational Fluid Dynamics (CFD) simulations, 3D printing and experimental testing. A 3D printed 10 mm hydrocyclone was shown first to match the performance of a ceramic equivalent, followed by factorial experiments with a set of printed hydrocyclones of different spigot and vortex finder diameters. A CFD model for small hydrocyclones was implemented and, following validation with the experimental data, used to simulate small hydrocyclone designs with parabolic walls. The model predicted improved separation performance compared to the conventional conic wall designs. In a novel development, a 10 mm hydrocyclone with parabolic walls was 3D printed and the prediction confirmed experimentally. The solids recovery and concentration ratio were increased by 10 percentage points and 0.2, respectively, for a 0.5 g/L yeast suspension and at an equivalent pressure drop. The use of 3D printing to manufacture small hydrocyclones of various designs has been proven in this study to be practical and to allow rapid prototyping design informed by CFD simulations. This is a significant improvement in the cost, time and versatility associated to hydrocyclone design and can lead to enhanced separation performance.

A new Petrov-Galerkin finite element method for two-dimensional (2D) highly advective flows in porous media, which removes numerical oscillations and retains its precision compared to the conventional Galerkin finite element method, is presented. A new continuous weighting function for quadratic elements is proposed. Moreover, a numerical scheme is developed to ensure the weighting factors are accurately determined for 2D non-uniform flows and 2D distorted elements. Finally, a series of numerical examples are performed to demonstrate the capability of the approach. Comparison against existing methods in the simulation of a benchmark problem further verifies the robustness of the proposed method.

Purpose: The morphological and hemodynamic evaluations of neurovascular diseases treated with stents would benefit from noninvasive imaging techniques such as 3D time-of-flight MRI (3D-TOF) and 3D phase contrast MRI (3D-PCMRI). For this purpose, a comprehensive evaluation of the stent artifacts and their impact on the flow measurement is critical., Methods: The artifacts of a representative sample of neurovascular stents were evaluated in vitro with 3D-TOF and 3D-PCMRI sequences. The dependency of the artifacts with respect to the orientation was analyzed for each stent design as well as the impact on the flow measurement accuracy. Furthermore, the 3D-PCMRI data of four patients carrying intracranial aneurysms treated with flow diverter stents were analyzed as illustrative examples., Results: The stent artifacts were mainly confined to the stent lumen therefore indicating the leading role of shielding effect. The influence of the stent design and its orientation with respect to the transmitting MR coils were highlighted. The artifacts impacted the 3D-PCMRI velocities mainly in the low magnitude domains, which were discarded from the analysis ensuring reliable near-stent velocities. The feasibility of in-stent flow measurements was confirmed in vivo on two patients who showed strong correlation between flow and geometric features. In two other patients, the consistency of out-of-stent velocities was verified qualitatively through intraaneurysmal streamlines except when susceptibility artifacts occurred., Conclusion: The present results motivate the conception of low inductance or non-conductive stent design. Furthermore, the feasibility of near-stent 3D-PCMRI measurements opens the door to clinical applications like the post-treatment follow-up of stenoses or intracranial aneurysms.

The main limitation of Computational Fluid Dynamics (CFD) lies in the unacceptable computational capability needed for performing accurate simulations for most real-time applications, and in the reduced accuracy of computationally more efficient low fidelity models for security-related applications. One example is the treatment of complex turbulent flows, where low-fidelity models introduce simplifications and source of uncertainties. A promising solution to improve accuracy is to use additional information about the actual flow field, such as experimental data taken on the system. The dynamic data-driven paradigm allows the direct incorporation of the knowledge coming from the measurements within the simulation, thus improving the model estimate itself by minimising its misfit with the data. In this work, the Kalman filter algorithm for data assimilation is combined with the segregated method for CFD modelling to get an integrated algorithm for resolving the incompressible Navier-Stokes equations along with the temperature one. The main novelty lies because such an integrated approach allows preserving mass conservation. This algorithm is herein validated regarding an instrumented cooling channel of the TRIGA Mark II reactor at the University of Pavia, using experimental data on temperature. The main takeaway of this validation is that, despite having only measurements on one quantity, also the prediction on velocity is improved regarding the standard segregated CFD algorithm. The prediction of the state also improves in domain locations where experimental data are not available. The increase in computational time is still lower than the one needed for a more accurate simulation.

Made available in DSpace on 2019-09-12T16:53:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2017 Computational fluid dynamics simulations have been employed in many engineering applications to improve machines and processes. In this study, CFD is used to analyse the effect of geometrical modifications of a discharge chute in the performance of a drying process of silica (SiO2) and water (H2O) compound. Multi-phase flow simulations were carried on to study the gas-solid flow inside discharge chute to determine internal pressure, velocity and temperature of the flow. The results for the modified geometry show a reduction in the flow velocity and in the pressure that can increase the flow rate of the compound and reduce material's sedimentation. The simple geometric modification of the discharge chute proposed in this study might reduce maintenance and lead to production efficiency gains. (C) 2017 Elsevier Ltd. All rights reserved. [Lamas, Wendell de Queiroz; Bargos, Fabiano Fernandes] Univ Sao Paulo, Lorena Sch Engn, Dept Basic & Environm Sci, BR-12602810 Lorena, SP, Brazil [Oscare Giacaglia, Giorgio Eugenio; Grandinetti, Francisco José; de Moura, Leandro] Universidade de Taubaté (Unitau), Dept Mech Engn, Postgrad Programme Mech Engn, BR-12060440 Taubate, SP, Brazil

A third-order numerical model based on one-dimensional computational fluid dynamics is developed for kinetic Stirling engines. Various loss mechanisms in Stirling engines, including gas spring hysteresis loss, shuttle loss, appendix displacer gap loss, gas leakage loss, finite speed loss, piston friction loss, pressure drop loss, heat conduction loss, mechanical loss and imperfect heat transfer, are considered and embedded into the basic control equations. The non-equilibrium thermal model is adopted for the regenerator to capture the oscillating features of the gas and solid temperatures. To improve the numerical stability and accuracy, the implicit second-order time difference scheme and the second-order upwind scheme are adopted for discretizing the time differential terms and convective terms, respectively. Experimental validations are then conducted on a beta-type Stirling engine with the extensive experimental data for diverse working conditions. The results show that the developed model has better accuracies than the previous second-order models. Good agreements are achieved for predicting various critical system parameters, including pressure-volume diagram, indicated power, brake power, indicated efficiency, brake efficiency and mechanical efficiency. In particular, both the experiments and simulations show that the Stirling engine charged with helium tends to have much lower optimal working frequencies and poorer performances compared to the hydrogen system. Based on the analyses of the losses, it reveals that the pressure drop in the flow channels plays a critical role in shaping the different behaviors. The pressure drop in the helium system is much larger and more sensitive to the frequency increase due to the much larger viscosity of gaseous helium. Hydrogen is a superior working gas for a Stirling engine. The transient characteristics of the oscillating flow and the associated thermal interactions between gas and solid in the regenerator are finally analyzed in order to have an insight of the complex thermodynamic process. The study provides a promising numerical approach in simulating Stirling engines for further understandings of their operating characteristics and the underling mechanisms.

This paper studies Kalman filtering applied to Reynolds-Averaged Navier–Stokes (RANS) equations for turbulent flow. The integration of the Kalman estimator is extended to an implicit segregated method and to the thermodynamic analysis of turbulent flow, adding a sub-stepping procedure that ensures mass conservation at each time step and the compatibility among the unknowns involved. The accuracy of the algorithm is verified with respect to the heated lid-driven cavity benchmark, incorporating also temperature observations, comparing the augmented prediction of the Kalman filter with the Computational Fluid-Dynamic solution found on a fine grid.

Spray-dried ceramic slip (hereinafter “atomized slip”) conveying is mainly carried out by belt conveyors. The bulk solid is picked up from the spray dryer bottom and then covers long distances, crossing the working environment and rising up to feed final stocking silos. Conveyor belts, without specific powder confinement devices, spread out fine particles, causing dust pollution and generating risk for workers' health (silicosis). Atomized slip pneumatic transport solves a problem of dust pollution caused by atomized slip belt conveying. However, atomized slip pneumatic conveying can be suitable only if some fluid-dynamical and thermo-hygrometric parameters are effectively under control. In fact, both solid maximum conveying velocity and speed gradient (i.e. the variation of solid velocity, in m/s, per meter of pipe length) need to be limited to guarantee product integrity and quality. Moreover, atomized slip humidity must be kept within a range (4–7% in weight) to give some specific characteristics to the final product. So, compressed air humidity, pressure and temperature need to be controlled all along the pipeline to avoid relevant atomized slip humidification or drying. The paper describes the design process and realization of an atomized slip pneumatic conveying test facility carried out to confirm fluid-dynamical conveying parameters. A finite element software simulator (TPSimWin) was used to evaluate and control atomized slip velocity, speed gradient, humidity and temperature along the pipeline.

A building needs to be designed for the whole period of its useful life according to its requirements. However, future climate predictions involve some uncertainty. Thus, several sustainable strategies of adaptation need to be incorporated after the initial design. In this sense, tunnel ventilation in broiler houses provides high air velocity values (2-3 m center dot s(-1)) at animal level to diminish their thermal stress and associated mortality. This ventilation system was experimentally incorporated into a Mediterranean climate. The aim was to resolve these thermal problems in hot seasons, as (traditional) cross-mechanical ventilation does not provide enough air velocity values. Surprisingly, very little information on tunnel ventilation systems is available, especially in terms of air velocity. Using Computational Fluid Dynamics (CFD) and a multi-sensor system, the average results are similar (at animal level: 1.59 +/- 0.68 m center dot s(-1) for CFD and 1.55 +/- 0.66 m center dot s(-1) for measurements). The ANOVA for validation concluded that the use of CFD or measurements is not significant (p-value = 0.1155). Nevertheless, some problems with air velocity distribution were found and need to be solved. To this end, CFD techniques can help by means of virtual designs and scenarios providing information for the whole indoor space., This work was funded by the project GV04B-511 (Generalitat Valenciana, Spain) and by the Vicerrectorado of Investigacion of the Universitat Politecnica de Valencia (Programa de Apoyo a la Investigacion y Desarrollo Multidisciplinar Project PAID register 2614).

Jan De Backer,1 Wim Vos,1 Cedric Van Holsbeke,1 Samir Vinchurkar,1 Rita Claes,2 Paul M Parizel,3 Wilfried De Backer2 1FluidDA nv, Kontich, Belgium; 2Department Respiratory Medicine, University Hospital, Antwerp, Belgium; 3Department Radiology, University Hospital, Antwerp, Belgium Background: Previous studies have demonstrated the potential beneficial effect of N-acetylcysteine (NAC) in chronic obstructive pulmonary disease (COPD). However, the required dose and responder phenotype remain unclear. The current study investigated the effect of high-dose NAC on airway geometry, inflammation, and oxidative stress in COPD patients. Novel functional respiratory imaging methods combining multislice computed tomography images and computer-based flow simulations were used with high sensitivity for detecting changes induced by the therapy. Methods: Twelve patients with Global Initiative for Chronic Obstructive Lung Disease stage II COPD were randomized to receive NAC 1800 mg or placebo daily for 3 months and were then crossed over to the alternative treatment for a further 3 months. Results: Significant correlations were found between image-based resistance values and glutathione levels after treatment with NAC (P = 0.011) and glutathione peroxidase at baseline (P = 0.036). Image-based resistance values appeared to be a good predictor for glutathione peroxidase levels after NAC (P = 0.02), changes in glutathione peroxidase levels (P = 0.035), and reduction in lobar functional residual capacity levels (P = 0.00084). In the limited set of responders to NAC therapy, the changes in airway resistance were in the same order as changes induced by budesonide/formoterol. Conclusion: A combination of glutathione, glutathione peroxidase, and imaging parameters could potentially be used to phenotype COPD patients who would benefit from addition of NAC to their current therapy. The findings of this small pilot study need to be confirmed in a larger pivotal trial. Keywords: functional respiratory imaging, computational fluid dynamics, computed tomography, chronic obstructive pulmonary disease, N-acetylcysteine

A review is presented for the research development of Stirling cycle engines for recovering low and moderate temperature heat. The Stirling cycle engines are categorized into four types, including kinetic, thermoacoustic, free-piston, and liquid piston types. The working characteristics, features, technological details, and performances of the related Stirling cycle engines are summarized. Upon comparing the available experimental results and the technology potentials, the research directions and the possible applications of different Stirling cycle engines are further discussed and identified. It is concluded that kinetic Stirling engines and thermoacoustic engines have the greatest application prospect in low and moderate temperature heat recoveries in terms of output power scale, conversion efficiency, and costs. In particular, kinetic Stirling engines should be oriented toward two directions for practical applications, including providing low-cost solutions for low temperatures, and moderate efficient solutions with moderate costs for medium temperatures. Thermoacoustic engines for low temperature applications are especially attractive due to their low costs, high efficiencies, superior reliabilities, and simplicities over the other mechanical Stirling engines. This work indicates that a cost effective Stirling cycle engine is practical for recovering small-scale distributed low-grade thermal energy from various sources.

The precise flow characteristics that promote different atherosclerotic plaque types remain unclear. We previously developed a blood flow-modifying cuff for ApoE −/− mice that induces the development of advanced plaques with vulnerable and stable features upstream and downstream of the cuff, respectively. Herein, we sought to test the hypothesis that changes in flow magnitude promote formation of the upstream (vulnerable) plaque, whereas altered flow direction is important for development of the downstream (stable) plaque. We instrumented ApoE −/− mice ( n = 7) with a cuff around the left carotid artery and imaged them with micro-CT (39.6 µm resolution) eight to nine weeks after cuff placement. Computational fluid dynamics was then performed to compute six metrics that describe different aspects of atherogenic flow in terms of wall shear stress magnitude and/or direction. In a subset of four imaged animals, we performed histology to confirm the presence of advanced plaques and measure plaque length in each segment. Relative to the control artery, the region upstream of the cuff exhibited changes in shear stress magnitude only ( p p

During a root canal treatment the root canal is irrigated with an antimicrobial fluid, commonly performed with a needle and a syringe. Irrigation of a root canal with two different types of needles can be modeled as an impinging axisymmetric or non-axisymmetric jet. These jets are investigated experimentally with high-speed Particle Imaging Velocimetry, inside and outside the confinement (concave surface) of a root canal, and compared to theoretical predictions for these jets. The efficacy of irrigation fluid refreshment with respect to the typical reaction time of the antimicrobial fluid with a biofilm is characterized with a non-dimensional Damkohler number. The pressure that these jets induce on a wall or at the apex of the root canal is also measured. The axisymmetric jet is found to be stable and its velocity agrees with the theoretical prediction for this type of jet, however, a confinement causes instabilities to the jet. The confinement of the root canal has a pronounced influence on the flow, for both the axisymmetric and non-axisymmetric jet, by reducing the velocities by one order of magnitude and increasing the pressure at the apex. The non-axisymmetric jet inside the confinement shows a cascade of eddies with decreasing velocities, which at the apex does not provide adequate irrigation fluid refreshment.

A testing apparatus for flame exposure of ablative, high thermal flux-resistant materials has been designed and manufactured according to the ASTM E 285-80 standard. The test is useful for the selection of thermal protection systems (TPS) working as ablators and for the evaluation of their shielding performance. In order to support the material/component design and to offer new and differentiated tools for the screening phase of TPS materials, a CFD (computational fluid-dynamics) model of the burning test was developed. The model simulates the combustion of an oxygen—acetylene mixture occurring in a conventional welding torch, and calculates the heat flux incident on the sample and the related temperature fields. The validation of the model was obtained performing suitable instrumented tests enabling direct measurements of both incident heat flux and temperatures of the front and back surfaces of an ablative sample. Good agreement was found between numerical results and experimental measurements, encouraging the use of simulations for the design of the test environmental conditions.

Polydispersed particles in reactive flows is a wide subject area encompassing a range of dispersed flows with particles, droplets or bubbles that are created, transported and possibly interact within a reactive flow environment - typical examples include soot formation, aerosols, precipitation and spray combustion. One way to treat such problems is to employ as a starting point the Newtonian equations of motion written in a Lagrangian framework for each individual particle and either solve them directly or derive probabilistic equations for the particle positions (in the case of turbulent flow). Another way is inherently statistical and begins by postulating a distribution of particles over the distributed properties, as well as space and time, the transport equation for this distribution being the core of this approach. This transport equation, usually referred to as population balance equation (PBE) or general dynamic equation (GDE), was initially developed and investigated mainly in the context of spatially homogeneous systems. In the recent years, a growth of research activity has seen this approach being applied to a variety of flow problems such as sooting flames and turbulent precipitation, but significant issues regarding its appropriate coupling with CFD pertain, especially in the case of turbulent flow. The objective of this review is to examine this body of research from a unified perspective, the potential and limits of the PBE approach to flow problems, its links with Lagrangian and multi-fluid approaches and the numerical methods employed for its solution. Particular emphasis is given to turbulent flows, where the extension of the PBE approach is met with challenging issues. Finally, applications including reactive precipitation, soot formation, nanoparticle synthesis, sprays, bubbles and coal burning are being reviewed from the PBE perspective. It is shown that population balance methods have been applied to these fields in varying degrees of detail, and future prospects are discussed.

Purpose An arteriovenous fistula (AVF) is the first choice vascular access for hemodialysis. The AVF pathway can be seen as consisting of seven segments: proximal artery, distal artery, arterial collaterals, proximal vein, distal vein, venous collaterals, and the anastomosis. While most studies describe access complications without considering the impact of the anastomosis (7th segment), the present mathematical study investigated the hemodynamic impact of anastomosis size and angle on pressure drop and flow distribution. Methods A side-to-end AVF model was developed, consisting of an anastomosis with a given cross-sectional area (substudy 1) and angle (substudy 2). Starting from two reference cases (one for each substudy) with fixed flow distribution, pressure drop over the anastomosis was calculated for an arterial inflow in the range 600 to 1200 ml/min. The same reference cases, subsequently with fixed pressure boundary conditions, were further used to assess flow distribution over the proximal vein and distal artery. Results Pressure drop decreased with a larger anastomosis cross-sectional area and an angle wider than 43°, while it was almost stable for smaller angles. Although proximal arterial inflow increased for larger anastomosis areas, the overall flow distribution shifted almost totally to the proximal vein. When the anastomosis angle exceeded 58°, the proximal arterial inflow was not sufficient to deliver enough flow, leading to distal arterial flow reversal. Conclusion Despite the underestimation of the hemodynamic impact of the anastomosis size and angle in the literature, this study showed major influences on the pressure drop over the anastomosis and, with it, on flow distribution towards the arterial and venous outflow.

The Doppler flow wave form and its derived measures such as the pulsatility index provide clinically important tools for the investigation of arterial disease. The typical shape of Doppler flow wave forms is physiologically known to be largely determined by both peripheral resistance and elastic properties of the arterial wall.In the present study we systematically investigate the influence of both vessel wall elasticity and peripheral resistance on the flow wave form obtained from a CFD-simulation of blood flow in the carotid bifurcation. Numerical results are compared to in vivo ultrasound measurements. The in vivo measurement provides a realistic geometry, local elasticities and an input flow wave form for the numerical experiment.Numerical and experimental results are compared at three different sites in the carotid branches. Peripheral resistance has a profoundly decreasing effect on velocities in the external carotid artery. If elasticity is taken into account, the computed peak systolic velocities are considerably lower and a more realistic smoothing of the flow wave form is found. Together, the results indicate that only if both vessel wall elasticity and positive peripheral resistance are taken into account, experimentally obtained Doppler flow wave forms can be reproduced numerically. (c) 2006 Elsevier Ltd. All rights reserved.

Pulsatile blood flow through the cavities of the heart and great vessels is time-varying and multidirectional. Access to all regions, phases and directions of cardiovascular flows has formerly been limited. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has enabled more comprehensive access to such flows, with typical spatial resolution of 1.5x1.5x1.5 - 3x3x3 mm(3), typical temporal resolution of 30-40 ms, and acquisition times in the order of 5 to 25 min. This consensus paper is the work of physicists, physicians and biomedical engineers, active in the development and implementation of 4D Flow CMR, who have repeatedly met to share experience and ideas. The paper aims to assist understanding of acquisition and analysis methods, and their potential clinical applications with a focus on the heart and greater vessels. We describe that 4D Flow CMR can be clinically advantageous because placement of a single acquisition volume is straightforward and enables flow through any plane across it to be calculated retrospectively and with good accuracy. We also specify research and development goals that have yet to be satisfactorily achieved. Derived flow parameters, generally needing further development or validation for clinical use, include measurements of wall shear stress, pressure difference, turbulent kinetic energy, and intracardiac flow components. The dependence of measurement accuracy on acquisition parameters is considered, as are the uses of different visualization strategies for appropriate representation of time-varying multidirectional flow fields. Finally, we offer suggestions for more consistent, user-friendly implementation of 4D Flow CMR acquisition and data handling with a view to multicenter studies and more widespread adoption of the approach in routine clinical investigations. Funding Agencies|Swedish Research Council; Medical Research Council of Southeast Sweden; Linkoping University; British Heart Foundation Centre of Research Excellence; Oxford NIHR Biomedical Research Centre; NIH [K25HL119608]; Swedish Heart and Lung Foundation; European Research Council [HEART4FLOW, 310612]; Radiological Society of North America (RSNA); NIHR Cardiovascular Biomedical Research Unit at the Royal Brompton and Harefield NHS Foundation Trust; Imperial College London; National Institutes of Health (NIH) National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) [R01 R01DK096169]; National Institute of Health (NIH) National Heart, Lung, and Blood Institute (NHLBI) [R01HL115828]

Background: The efficacy of inhaled corticosteroids (ICS) in moderately severe COPD patients remains unclear. At the same time, the use of extrafine particles in COPD patients is a topic of ongoing research. Objectives: This study assessed the effect of ICS in steroid-naive mild COPD patients and the effect of reducing the ICS dose in more severe COPD patients previously using ICS when switching to an extrafine particle BDP/F formulation (Foster using Modulite technology, Chiesi Pharmaceutici, Parma, Italy). Methods: Novel functional respiratory imaging (FRI) methods, consisting of multi-slice CT scans and Computational Fluid Dynamics, were used in combination with conventional pulmonary function tests and patient reported outcomes. Results: The study showed that the administration of extrafine BDP/F after 4-6 h led to a significant improvement in lung function parameters and hyperinflation as determined by spirometry, body plethysmography, and functional respiratory imaging. After 6 months of treatment, it was observed that, compared to baseline, the hyperinflation on lobar level at total lung capacity was significantly reduced (-1.19 +/- 7.19 %p, p=0.009). In addition, a significant improvement in SGRQ symptom score was noted in the entire patient population. Patients who improved in terms of hyperinflation also improved their MMRC dyspnea score. CFD indicated a difference in regional deposition between extrafine and non-extrafine formulations with -11% extrathoracic deposition and up to +4% lobe deposition for the extrafine formulation. Conclusions: The study showed that the administration of extrafine BDP/F improved lung function parameters and hyperinflation. Patients previously treated with ICS remained stable despite the lower dose, while ICS naive patients improved in terms of lobar hyperinflation. FRI seems to be a sensitive biomarker to detect clinically relevant changes that are not detected by spirometry. The next step is to confirm these findings in a controlled trial.

Introduction: Abnormal fluid mechanical environment in the pre-natal cardiovascular system is hypothesized to play a significant role in causing structural heart malformations. It is thus important to improve our understanding of the prenatal cardiovascular fluid mechanical environment at multiple developmental time-points and vascular morphologies. We present such a study on fetal great arteries on the wildtype mouse from embryonic day 14.5 (E14.5) to near-term (E18.5). Methods: Ultrasound bio-microscopy (UBM) was used to measure blood velocity of the great arteries. Subsequently, specimens were cryo-embedded and sectioned using episcopic fluorescent image capture (EFIC) to obtain high-resolution 2D serial image stacks, which were used for 3D reconstructions and quantitative measurement of great artery and aortic arch dimensions. EFIC and UBM data were input into subject-specific computational fluid dynamics (CFD) for modeling hemodynamics. Results: In normal mouse fetuses between E14.5-18.5, ultrasound imaging showed gradual but statistically significant increase in blood velocity in the aorta, pulmonary trunk (with the ductus arteriosus), and descending aorta. Measurement by EFIC imaging displayed a similar increase in cross sectional area of these vessels. However, CFD modeling showed great artery average wall shear stress and wall shear rate remain relatively constant with age and with vessel size, indicating that hemodynamic shear had a relative constancy over gestational period considered here. Conclusion: Our EFIC-UBM-CFD method allowed reasonably detailed characterization of fetal mouse vascular geometry and fluid mechanics. Our results suggest that a homeostatic mechanism for restoring vascular wall shear magnitudes may exist during normal embryonic development. We speculate that this mechanism regulates the growth of the great vessels., NA

An aortic dissection (AD) is a serious condition defined by the splitting of the arterial wall, thus generating a secondary lumen [the false lumen (FL)]. Its management, treatment and follow-up are clinical challenges due to the progressive aortic dilatation and potentially severe complications during follow-up. It is well known that the direction and rate of dilatation of the artery wall depend on haemodynamic parameters such as the local velocity profiles, intra-luminal pressures and resultant wall stresses. These factors act on the FL and true lumen, triggering remodelling and clinical worsening. In this study, we aimed to validate a computational fluid dynamic (CFD) tool for the haemodynamic characterisation of chronic (type B) ADs. We validated the numerical results, for several dissection geometries, with experimental data obtained from a previous in vitro study performed on idealised dissected physical models. We found a good correlation between CFD simulations and experimental measurements as long as the tear size was large enough so that the effect of the wall compliance was negligible.

We used a multiphysics model to assess the accuracy of carotid strain estimates derived from a 1-D ultrasonic wall tracking algorithm. The presented tool integrates fluid-structure interaction (FSI) simulations with an ultrasound simulator (Field II), which allows comparison of the ultrasound (US) images with a ground truth. Field II represents tissue as random points on which US waves reflect and whose position can be updated based on the flow field and vessel wall deformation from FSI. We simulated the RF-signal of a patient-specific carotid bifurcation, including the blood pool as well as the vessel wall and surrounding tissue. Distension estimates were obtained from a wall tracking algorithm using tracking points at various depths within the wall, and further processed to assess radial and circumferential strain. The simulated data demonstrated that circumferential strain can be estimated with reasonable accuracy (especially for the common carotid artery and at the lumen-intima and media-adventitia interface), but the technique does not allow to reliably assess intra-arterial radial strain. These findings were supported by in vivo data of 10 healthy adults, showing similar circumferential and radial strain profiles throughout the arterial wall. We concluded that these deviations are present due to the complex 3-D vessel wall deformation, the presence of specular reflections and, to a lesser extent, the spatially varying beam profile, with the error depending on the phase in the cardiac cycle and the scanning location.

Numerical simulations of the microclimate inside a greenhouse canopy were validated. Experiments were conducted inside a 100 m(2) greenhouse compartment with a shading screen and potted Impatiens plants grown on benches. The greenhouse was equipped with a set of sensors, including a sonic and hot-bulb anemometers, thermocouples, air-humidity/temperature probes and balances. Thermal and water vapour exchanges between the crop and its environment were studied using 2D simulations of the microclimate carried out at a daily time scale within a calculation domain reduced to a parallelepiped, including the plants. The Navier-Stokes equations were solved using the standard k - epsilon turbulence model. A crop submodel which considers the crop as a porous medium and adds specific source terms for latent and sensible heat transfers was used. Two contrasting days with relatively high and low solar insulations were considered. For both cases, the computational fluid dynamics (CFD) model showed its ability to simulate the air temperature inside the canopy as well as the vertical distribution of the leaf temperatures throughout the day. It predicted the decrease of leaf temperature from the top to the bottom of the crop with good accuracy. It also provided a good estimation for the trend of transpiration rate throughout the day (coefficients of determination >0.92). Differences between the measured and simulated integrated transpiration rates over 24 h-periods remained < 15%. Consequently, the model could be useful to assess the water requirements of a crop for the purpose of adapting irrigation management to meet plant needs.

International audience; This article presents numerical simulations of the distribution of climate parameters within a ventilated tunnel tomato greenhouse during variable outside conditions. The simulations were performed using a computational fluid dynamics (CFD) code that solved the transport equations in a 3D domain, including the greenhouse and its crop stands, the surrounding ambient air and the soil located directly under the greenhouse. Radiative heat transfers were modeled using a bi-band discrete ordinates (DO) model, and the crop was considered to be a porous medium. Sensible and latent heat transfer between leaves and the surrounding air were determined based on the energy balance that included longwave and short-wave radiation fluxes in each crop control volume. The climatic boundary conditions were determined using experimental measurements, and the sun position was calculated for each time interval that was considered. The temperature distribution in the soil was determined based on a preliminary CFD determination of the conductive heat transfer in a 1D soil column. Simulations in the entire 3D domain were then performed, and 1 h time step and boundary conditions were updated prior to each calculation procedure. Results are presented for the spring equinox and summer solstice. These results highlight the combined influence of sun position, wind direction and intensity on the greenhouse microclimate and especially on the evapotranspiration rate of the crop at the leaf level. We discuss the possibility of using CFD code integration as a conceptual tool for designers or in association with a control climate model for farmers. (C) 2011 Elsevier Ltd. All rights reserved.

International audience; One-dimensional (1-D) simulation is a useful technique for the evaluation of dryer operating parameters and product properties before conducting real spray drying trials. The main advantage of a 1-D simulation tool is its ability to perform fast calculations with significant simplicity. Mathematical models can be formulated using heat, mass and momentum balances at the droplet level to estimate time-dependent gas and droplet parameters. One of the purposes of this paper is to summarize key mathematical models that may be used to perform 1-D simulation for spray drying processes, predict essential product-drying gas parameters, assess the accuracy of prediction using pilot-scale spray drying data and perhaps most importantly address the main benefits and limitations of the 1-D simulation technique in relation to industrial spray drying operations. The results of a recent international collaborative study on the development of spray drying process optimization software for skim milk manufacture are presented as an example of the application of 1-D simulation in milk processing.; La simulation monodimensionnelle (1-D) est une technique utile pour évaluer les paramètres de séchage et les propriétés des produits avant de conduire les essais de séchage en réel. Le principal avantage de l'outil de simulation 1-D est sa capacité à réaliser des calculs rapidement et avec une grande simplicité. Les modèles mathématiques peuvent être formulés avec les équilibres de chaleur, de masse et de quantité de mouvement à l'échelle de la gouttelette pour estimer les paramètres de vapeur et de gouttelette qui varient au cours du temps. Un des objectifs de cet article est de présenter de façon synthétique les modèles mathématiques clés qui peuvent être utilisés pour réaliser une simulation 1-D, prédire les paramètres de vapeur essentiels pour le séchage du produit, évaluer la précision de la prédiction en utilisant les données du séchage par atomisation obtenues à l'échelle pilote, et enfin d'aborder les principaux bénéfices et limites de la technique de simulation 1-D en relation avec les opérations de séchage par atomisation industrielles. Les résultats d'une récente étude réalisée en collaboration internationale sur le développement d'un logiciel d'optimisation du procédé de séchage par atomisation pour la production de poudre de lait écrémé sont présentés pour illustrer l'application de la simulation 1-D.

Ventilation processes inside the greenhouse strongly affect air renewal and internal climatic conditions, which themselves interact with the growth and homogeneity of the crop. Natural ventilation is often chosen since it is the most economic method available. Studies of internal distributed climate induced by ventilation have been taking place for the past 25 years. Experimental studies have pointed out the impact of vent configurations on airflow pattern, particularly when the wind is the main driving force. However, the development of computational fluid dynamics (CFDs) has only recently provided the opportunity to simulate the climate inside greenhouses for known vent configurations, and to test a wide range of geometries with different vent combinations under different climatic conditions. In this article, the main factors governing air movements inside the greenhouse are first analysed. The characteristics of the laboratory scale models and field experiments are reviewed, with particular focus on the technologies implemented. The principles of CFD, the main modelling approach, together with its adaptations to greenhouse climate simulation, are then described in detail. Conclusions of studies concerning ventilation efficiency inside greenhouses are reviewed with respect to greenhouse geometry and opening arrangements. Other parameters affecting ventilation, such as wind speed and direction, the addition of insect-proof or shading screens, and interactions with the crop, are also discussed.

In grass conservation systems, the field drying process of cut grass is an important function since it determines subsequent losses and possible hazardous effects of during silage. The drying process of harvested grass was evaluated using two different numerical approaches. Firstly, an existing experimentally-verified analytical model was used. Several parameters were improved from previous studies such as the evaluation of stomata conductance from outside climate variables. Secondly, a CFD modelling approach was applied to open field drying process of the biomass. The cut biomass in the field was simulated using the equivalent macro-porous medium approach. Experimental values were used to obtain realistic and accurate boundary conditions. The developed CFD model was validated using the existing analytical model that is based on evaporations as estimated from the Penman equation. An acceptable agreement between simulated and measured values of water content was obtained. The mean difference in the estimated outputs from the two models was 8%. Condensation occurred during the night and was correctly simulated by both types of models. In general, a good correspondence was found between the two approaches. The use of the CFD model reveals the climate heterogeneity in the grass area and also, creates the possibility of applying the model as a decision support model for an enhanced treatment of the grass after cutting.

Three different cyclist positions were evaluated with Computational Fluid Dynamics (CFD) and wind-tunnel experiments were used to provide reliable data to evaluate the accuracy of the CFD simulations. Specific features of this study are: (1) both steady Reynolds-averaged Navier-Stokes (RANS) and unsteady flow modelling, with more advanced turbulence modelling techniques (Large-Eddy Simulation - LES), were evaluated; (2) the boundary layer on the cyclist's surface was resolved entirely with low-Reynolds number modelling, instead of modelling it with wall functions; (3) apart from drag measurements, also surface pressure measurements on the cyclist's body were performed in the wind-tunnel experiment, which provided the basis for a more detailed evaluation of the predicted flow field by CFD. The results show that the simulated and measured drag areas differed about 11% (RANS) and 7% (LES), which is considered to be a close agreement in CFD studies. A fair agreement with wind-tunnel data was obtained for the predicted surface pressures, especially with LES. Despite the higher accuracy of LES, its much higher computational cost could make RANS more attractive for practical use in some situations. CFD is found to be a valuable tool to evaluate the drag of different cyclist positions and to investigate the influence of small adjustments in the cyclist's position. A strong advantage of CFD is that detailed flow field information is obtained, which cannot easily be obtained from wind-tunnel tests. This detailed information allows more insight in the causes of the drag force and provides better guidance for position improvements. ispartof: Journal of Biomechanics vol:43 issue:7 pages:1262-1268 ispartof: location:United States status: published

Peer-reviewed journal paper published in 2009 about the international modelling exercise conducted in 2006. An international study of fire modelling was conducted prior to the Dalmarnock Fire Test One in order to assess the state-of-the-art of fire simulations using a round-robin approach. This test forms part of the Dalmarnock Fire Tests, a series of experiments conducted in 2006 in a high-rise building. The philosophy behind the tests was to provide measurements in a realistic fire scenario involving multiple fuel packages and non-trivial fire growth, and with an instrumentation density suitable for comparison with computational fluid dynamics models. Each of the seven round-robin teams independently simulated the test scenario a priori using a common detailed description of the compartment geometry, fuel packages, ignition source and ventilation conditions. The aim of the exercise was to forecast the fire development as accurately as possible and compare the results. The aim was not to provide an engineering analysis with conservative assumptions or safety factors. Comparison of the modelling results shows a large scatter and considerable disparity among the predictions, and between predictions and experimental measurements. The scatter of the simulations is much larger than the error and variability expected in the experiments. The study emphasises on the inherent difficulty of modelling fire dynamics in complex fire scenarios like Dalmarnock, and shows that the accuracy to predict fire growth (i.e. evolution of the heat released rate) is, in general, poor.

http://www.actahort.org/members/showpdf?session=10447; When the transpiration of plants is low, the climate inside a greenhouse mainly results from a coupling of convective and radiative exchanges through the cover and ground. However up to now, this coupling has been hardly investigated through numerical techniques. A CFD model was thus implemented to investigate the airflow and temperature patterns inside a glasshouse during daytime, by solving simultaneously the radiative transfer and the energy equations. Simulations were carried out on a four-span compartmentalised glasshouse. The greenhouse was covered with a 4 mm thick horticulture glass and equipped with continuous roof vents. A two dimensional steady state CFD model was developed by using commercial software. The mathematical model solves the Navier-Stokes equations with the Boussinesq assumption and a k - epsilon turbulence model. Solar and atmospheric radiations are included by using a bi-band (distinguishing short and long wave length) radiation model. The analysis focuses not only on the ventilation rate but also on the heterogeneity of the climatic parameters in the canopy vicinity. The model was first partially validated by comparing measured and simulated temperatures inside the greenhouse and along the walls. Numerical predictions of the climate were then obtained for various ventilator configurations (windward only, leeward only and a combination of both). They offer a detailed view of the spatial velocity and temperature distributions and can be used as a tool to assess the characteristics of the ventilation process. The windward vent case generates the highest ventilation rate; nevertheless, the symmetric case ensures a better homogenization of the temperature and velocity. The best compromise between ventilation and homogenization of climatic parameters at the plant level is found by combining a windward roof vent for the windward span and symmetric roof vents for the rest of the greenhouse.

A three-dimensional model for the simulation of inductively coupled plasma torches (ICPTs) working at atmospheric pressure has been developed, using customized CFD commercial code FLUENT©. The helicoidal coil is taken into account in its actual 3-D shape, showing its effects on the plasma discharge for various geometric, electric and operating conditions. The electromagnetic equations are solved in their vector potential form, while the steady flow and energy equations are solved for optically thin plasmas under the assumptions of LTE and laminar flow; some of the results that will be presented have been obtained by means of an improved turbulent version of the 3-D model. Simulations are performed over a network cluster of double processor calculators in order to use the full capabilities of the 3-D modelling to describe the gas injection section of an industrial TEKNA PL-35 plasma torch without geometry simplifications, in order to perform a more realistic simulation of the inlet region of the discharge. In order to evaluate the importance of various 3-D effects on calculated plasma temperature and flow fields, our new results have been tested against the ones obtainable from 2-D models and from improved 2-D model that includes 3-D coil effects. Three-dimensional results concerning different operating conditions are presented, together with simulations of the trajectory and heating history of powders injected in the torch through a carrier gas.

This paper describes the use of an a posteriori error estimator to control anisotropic mesh adaptation for computing inviscid compressible flows. The a posteriori error estimator and the coupling strategy with an anisotropic remesher are first introduced. The mesh adaptation is controlled by a single-parameter tolerance (TOE) in regions where the solution is regular, whereas a condition on the minimal element size h(min) is enforced across Solution discontinuities. This h(min) condition is justified on the basis of an asymptotic analysis. The efficiency of the approach is tested with a supersonic flow over an aircraft. The evolution of a mesh adaptation/flow solution loop is shown, together with the influence of the parameters TOL and h(min). We verify numerically that the effect of varying h(min) is concordant with the conclusions of the asymptotic analysis, giving hints on the selection of h(min) with respect to TOL. Finally, we check that the results obtained with the a posteriori error estimator are at least as accurate as those obtained with anisotropic a priori error estimators. All the results presented can be obtained using a standard desktop computer, showing the efficiency of these adaptative methods. Copyright (C) 2008 John Wiley & Sons, Ltd.