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Particle Image Velocimetry (PIV) measurements with the aim of providing experimental data for the SimInhale benchmark case are presented within this work. We, therefore, present a refractive index matched, transparent model of the benchmark geometry, in which the velocity and turbulent kinetic energy fields are examined at flow rates comparable to 15, 30 and 60 L/min (Re ≈ 1000–4500) in air. Furthermore, these results are compared with Large Eddy Simulations (LES). The results reveal a Reynolds number independence of the qualitative velocity field in the range covered within this work. Good agreement is found between the PIV and LES data, with a slight over-prediction of turbulent kinetic energies by the simulations. The obtained experimental data will be part of a common, publicly accessible ERCOFTAC database along with additional results published recently. 133 183 189

It is widely acknowledged that inhaled fibers, e.g. air pollutants and anthropogenic particulate matter, hold the ability to deposit deep into the lungs reaching the distal pulmonary acinar airways as a result of their aerodynamic properties; these particles tend to align with the flow and thus stay longer airborne relative to their spherical counterpart, due to higher drag forces that resist sedimentation. Together with a high surface-to-volume ratio, such characteristics may render non-spherical particles, and fibers in particular, potentially attractive airborne carriers for drug delivery. Until present, however, our understanding of the dynamics of inhaled aerosols in the distal regions of the lungs has been mostly limited to spherical particles. In an effort to unravel the fate of non-spherical aerosols in the pulmonary depths, we explore through numerical simulations the kinematics of ellipsoid-shaped fibers in a toy model of a straight pipe as a first step towards understanding particle dynamics in more intricate acinar geometries. Transient translational and rotational motions of micronsized ellipsoid particles are simulated as a function of aspect ratio (AR) for laminar oscillatory shear flows mimicking various inhalation maneuvers under the influence of aerodynamic (i.e. drag and lift) and gravitational forces. We quantify transport and deposition metrics for such fibers, including residence time and penetration depth, compared with spherical particles of equivalent mass. Our findings underscore how deposition depth is largely independent of AR under oscillatory conditions, in contrast with previous works where AR was found to influence deposition depth under steady inspiratory flow. Overall, our efforts underline the importance of modeling oscillatory breathing when predicting fiber deposition in the distal lungs, as they are inhaled and exhaled during a full inspiratory cycle. Such physical insight helps further explore the potential of fiber particles as attractive carriers for deep airway targeting.

The focus of the work is the “phase lock-on”, a well-known phenomenon observed in oscillating dynamical systems where the forcing and output frequencies are synchronized. This phenomenon appears to be universal with the frequencies related by a rational ratio. We considered the case of an incompressible flow past a confined cylinder where the incident bulk flow is subjected to periodic velocity perturbations. While we considered both Newtonian and non-Newtonian (Bingham) fluids, the main interest was on the Bingham case. Numerical simulations were conducted at a fixed Reynolds number of Re = 100 based on the bulk fluid velocity and cylinder diameter. The relative amplitude of the periodic velocity perturbation was considered in the range 0.10–0.30 and the forcing frequency relative to the natural unforced shedding frequency was in the range 1.4–2.3. These choices yielded fixed lock-on periodic states that correspond to the number 2 on the horizontal axis of an Arnold tongue graph. Yield stress effects are shown for Bingham numbers in the range 0–0.5.

Despite the prevalence of inhalation therapy in the treatment of pediatric respiratory disorders, most prominently asthma, the fraction of inhaled drugs reaching the lungs for maximal efficacy remains adversely low. By and large drug delivery devices and their inhalation guidelines are typically derived from adult studies with child dosages adapted according to body weight. While it has long been recognized that physiological (e.g. airway sizes, breathing maneuvers) and physical transport (e.g. aerosol dynamics) characteristics are critical in governing deposition outcomes, such knowledge has yet to be extensively adapted to younger populations. Motivated by such shortcomings, the present work leverages in a first step in silico computational fluid dynamics (CFD) to explore opportunities for augmenting aerosol deposition in children based on respiratory physiological and physical transport determinants. Using an idealized, anatomically-faithful upper airway geometry, airflow and aerosol motion are simulated as a function of age, spanning a five year old to an adult. Breathing conditions mimic realistic age-specific inhalation maneuvers representative of Dry Powder Inhalers (DPI) and nebulizer inhalation. Our findings point to the existence of a single dimensionless curve governing deposition in the conductive airways via the dimensionless Stokes number (Stk). Most significantly, we uncover the existence of a distinct deposition peak irrespective of age. For the DPI simulations, this peak (∼ 80%) occurs at Stk ≈ 0.06 whereas for nebulizer simulations, the corresponding peak (∼ 45%) occurs in the range of Stk between 0.03-0.04. Such dimensionless findings hence translate to an optimal window of micron-sized aerosols that evolves with age and varies with inhalation device. The existence of such deposition optima advocates revisiting design guidelines for optimizing deposition outcomes in pediatric inhalation therapy. 13 11

Regional deposition of inhaled medicines is a valuable metric of effectiveness in drug delivery applications to the lung. In silico methods are now emerging as a valuable tool for the detailed description of localized deposition in the respiratory airways. In this context, there is a need to minimize the computational cost of high-fidelity numerical approaches. Motivated by this need, the present study is designed to assess the role of the extrathoracic airways in determining regional deposition in the upper bronchial airways. Three mouth-throat geometries, with significantly different geometric and filtering characteristics, are merged onto the same tracheobronchial tree that extends to generation 8, and Large Eddy Simulations are carried out at steady inhalation flowrates of 30 and 60 L / min . At both flowrates, large flow field differences in the extrathoracic airways across the three geometries largely die out below the main bifurcation. Importantly, localized deposition fractions are found to remain practically identical for particles with aerodynamic diameters of up to d p = 4 μ m and d p = 2.5 μ m at 30 and 60 L / min , respectively. For larger particles, differences in the localized deposition fractions are shown to be mainly due to variations in the mouth-throat filtering rather than upstream flow effects or differences in the local flow field. Deposition efficiencies in the individual airway segments exhibit strong correlations across the three geometries, for all particle sizes. The results suggest that accurate predictions of regional deposition in the tracheobronchial airways can therefore be obtained if the particle size distribution that escapes filtering in the mouth-throat (ex-cast dose) of a particular patient is known or can be estimated. These findings open the prospect for significant reductions in the computational expense, especially in the context of in silico population studies, where the aerosol size distribution and precomputed flow field from standardized mouth-throat models could be used with large numbers of tracheobronchial trees available in chest-CT databases.

Regional deposition effects are important in the pulmonary delivery of drugs intended for the topical treatment of respiratory ailments. They also play a critical role in the systemic delivery of drugs with limited lung bioavailability. In recent years, significant improvements in the quality of pulmonary imaging have taken place, however the resolution of current imaging modalities remains inadequate for quantifying regional deposition. Computational Fluid-Particle Dynamics (CFPD) can fill this gap by providing detailed information about regional deposition in the extrathoracic and conducting airways. It is therefore not surprising that the last 15 years have seen an exponential growth in the application of CFPD methods in this area. Survey of the recent literature however, reveals a wide variability in the range of modelling approaches used and in the assumptions made about important physical processes taking place during aerosol inhalation. The purpose of this work is to provide a concise critical review of the computational approaches used to date, and to present a benchmark case for validation of future studies in the upper airways. In the spirit of providing the wider community with a reference for quality assurance of CFPD studies, in vitro deposition measurements have been conducted in a human-based model of the upper airways, and several groups within MP1404 SimInhale have computed the same case using a variety of simulation and discretization approaches. Here, we report the results of this collaborative effort and provide a critical discussion of the performance of the various simulation methods. The benchmark case, in vitro deposition data and in silico results will be published online and made available to the wider community. Particle image velocimetry measurements of the flow, as well as additional numerical results from the community, will be appended to the online database as they become available in the future. This article is based upon work from COST Action MP1404 SimInhale ‘Simulation and pharmaceutical technologies for advanced patient-tailored inhaled medicines', supported by COST (European Cooperation in Science and Technology) www.cost.eu. The work conducted at Brno University of Technology was partly supported by the Czech Science Foundation [16-23675S].

The purpose of this research was to determine the influence of inspiratory flow rate and relative humidity on particle size distributions (PSDs) generated by three MDI inhalers (Flutiform, Fullhale and Ventolin) and one DPI inhaler (Spiriva). Particle size distribution was measured by APS 3321 (TSI, USA) for three different inspiratory flow rates – 30, 60 and 90 l/min. Aerosol from individual inhalers was led through a stainless steel tubing simulating the geometry of the human respiratory tract. The hygroscopicity of the particles was determined by comparing data obtained at laboratory conditions and at relative humidity of 90%. During the measurements of number PSDs by using of APS spectrometer, we measured bimodal distributions for Flutiform and Fullhale and monomodal distributions for Ventolin and DPI Spiriva. The increasing inspiratory flow rate had a minimal effect on the position of the modes of the individual distributions. The differences in PSD, measured under ambient conditions and at RH of 90%, were minimal and did not significantly affect the assumed probability of drug deposition. The results showed that determination of the PSDs by online spectrometer is a suitable alternative to traditional methods of measuring the particle size distributions of inhalation aerosol by NGI impactor.

Predicting regional deposition patterns of inhaled aerosols is important for the design and optimization of pharmaceutical formulations. © 2018, Springer International Publishing AG. 24 351 357 351-357

To be able to predict the fate of therapeutic or pollutant xenobiotic inhaled particles in the human lungs, we need to understand the nature of airflow as it occurs throughout the entire respiratory tract. © 2018, Springer International Publishing AG. 24 343 349 343-349

High-fidelity simulations of the complete airway tree are still largely beyond current computational capabilities. Towards large-scale simulations of the human lung, the current study introduces a numerical methodology to predict particle deposition in a simplified approximation of the deep lung during a full breathing cycle. The geometrical model employed consists of an idealised bronchial tree that represents generations 10 to 19 of the conducting zone and a heterogeneous acinar model created using a space-filling algorithm. The computational cost of the coupled simulation is reduced by taking advantage of the flow similarity across the central conducting regions in order to decompose the bronchial tree into representative subunits. Topological information is used to account for the correct gravitational force on the particles in the representative bifurcations, emulating their transport characteristics in the actual bronchial tree. Eventually, airflow and particle transport are simulated in a single representative bifurcation and a single acinar model, resulting in great savings in computational cost. An Eulerian-Lagrangian approach has been used for solving the flow and particle equations during sinusoidal breathing in the decomposed domain. The resulting deposition estimates agree rather well with the known deposition trends reported in the literature, while offering additional insights. For 1 − 5μm particles, deposition during exhalation is comparable to deposition upon inhalation, suggesting the use of breath-hold maneuvers to further increase sedimentation of these particles. Airway orientation relative to gravity was found to have a significant impact on deposition rates, especially for particles above 2μm and to be higher in the more distal generations, due to the wider range of angles relative to the direction of gravity. In the acinus, particles in the 2 − 5μm range have a quite high average deposition efficiency that reaches approximately 75% and shows considerable variation (12.4%) due to airway orientation. Finally, a simplified semi-analytical approach is introduced that can lead to even further reduction in computational costs, while incurring only a small loss in accuracy. © 2017 Elsevier B.V. 113 132 144 132-144

Recent developments in the prediction of local aerosol deposition in human lungs are driven by the fast development of computational simulations. Although such simulations provide results in unbeatable resolution, significant differences among distinct methods of calculation emphasize the need for highly precise experimental data in order to specify boundary conditions and for validation purposes. This paper reviews and critically evaluates available methods for the measurement of single and disperse two-phase flows for the study of respiratory airflow and deposition of inhaled particles, performed both in vivo and in replicas of airways. Limitations and possibilities associated with the experimental methods are discussed and aspects of the computational calculations that can be validated are indicated. The review classifies the methods into following categories: 1) point-wise and planar methods for velocimetry in the airways, 2) classic methods for the measurement of the regional distribution of inhaled particles, 3) standard medical imaging methods applicable to the measurement of the regional aerosol distribution and 4) emerging and nonconventional methods. All methods are described, applications in human airways studies are illustrated, and recommendations for the most useful applications of each method are given. © 2017 Elsevier B.V. 113 95 131 95-131

The mouth-throat plays a key role in the administration of inhaled medicines. It is an area of intense filtration, where an unacceptably high fraction of the released drug dose is deposited and thus wasted. Due to the relatively high flow rate associated with Dry Powder Inhalers (DPIs), drug particles are released at a high velocity, which causes substantial deposition in the oral cavity and the throat region by inertial impaction. Hence, reducing the mouththroat deposition is of utmost importance and this can only be achieved by designing more efficient inhaler devices (functioning at lower flow rates) and by obtaining a better understanding of the mechanisms that cause the oropharyngeal losses. The present study is designed to identify the main factors that determine aerosol deposition (unwanted filtering) in the mouththroat region, with the aim of controlling the leading effects that contribute to the oropharyngeal deposition losses for drugs delivered via DPIs. For this reason micron-sized particles are released and tracked in a patient-specific MRI-based mouth-throat geometry under three inhalation flow rates (15L/min, 30L/min, 60L/min), three head positions (straight, up, left), and three inhaler mouthpiece orientations (0o, 15o, 30o). Direct Numerical Simulations (DNS) are performed for the low flow rate using prescribed laminar inlet conditions, while Large Eddy Simulations (LES) are performed for the intermediate and high flow rates using fullydeveloped turbulent inlet conditions. Interestingly, our results reveal that the deposition fraction is insensitive to the head position, whilst the inhalation flow rate and the inhaler mouthpiece orientation have a strong influence on the aerosol deposition in the mouth-throat region. Furthermore, we illustrate the mean flow structures and examine their effect on the particle deposition of various micron sizes. Despite the fact that our results are case specific, we expect the main trends to be universal. 1

We present an extension that allows a recently proposed structure-based model for turbulent scalar transport to account for buoyancy effects. The proposed model is based on a generalization of the Interactive Particle Representation Model (IPRM) and is accompanied by a four-equation transport model that provides the turbulence scales needed for the closure of the complete structure-based model (SBM). The structure tensors and their invariants are used to model the additional buoyancy terms that emerge in the four-equation transport equations. Model parameters are set by matching the asymptotic decay exponents in decaying turbulence. The validity of the model is considered for a large number of different types of stably stratified flows at different Richardson numbers (Ri), showing encouraging results. The complete structure-based model achieves fair agreement with LES and DNS predictions for vertical shear in the presence of vertical mean stratification, while the structure tensors are shown to be suitable for use as diagnostic tools for the morphology of highly anisotropic turbulent structures. Additionally, the proposed model is shown to be sensitive to the variation of the inclination angle θ between the direction of the mean velocity gradient and the orientation of the mean scalar gradient. Furthermore, the model correctly predicts that the evolution of the inverse shear parameter is insensitive to the choice of inclination angle, yielding a turbulent Prandtl number close to unity, in accordance with DNS results. © 2016 The Authors 65 309 322 309-322

This paper presents direct numerical simulations (DNS) of fully developed turbulent liquid-metal flow in a circular duct entering a magnetic field. The case of a magnetohydrodynamic flow leaving a strong magnetic field has been extensively studied experimentally and numerically owing to its similarity to typical flow configurations appearing in liquid metal blankets of nuclear fusion reactors. Although also relevant to the design of fusion reactor blankets, the flow entering the fringing field of a magnet remains unexplored because its high intricacy precludes any simplification of the governing equations. Indeed, the complexity of the magnetohydrodynamic-turbulence interaction can only be analysed by direct numerical simulations or experiments. With that purpose, this paper addresses the case of a fully developed turbulent flow (Re τ ≈ 520) entering low, intermediate and strong magnetic fields under electrically insulating and poorly conducting walls by means of three-dimensional direct numerical simulations. Purely hydrodynamic computations (without the effect of the magnetic field) reveal an excellent agreement against previous experimental and numerical results. Current MHD results provide a very detailed information of the turbulence decay and reveal new three-dimensional features related to liquid-metal flow entering strong increasing magnetic fields, such as flow instabilities due to the effect of the Lorentz forces within the fringing region at high Ha numbers. © 2013 Elsevier B.V. © 2013 Published by Elsevier B.V. 88 3108 3124 3108-3124

A structure-based model has been constructed, for the first time, for the study of passive scalar transport in turbulent flows. The scalar variance and the large-scale scalar gradient variance are proposed as the two turbulence scales needed for closure of the scalar equations in the framework of the Interacting Particle Representation Model (IPRM). The scalar dissipation rate is modeled in terms of the scalar variance and the large-scale enstrophy of the velocity field. Model parameters are defined by matching the decay rates in freely isotropic turbulence. The model is validated for a large number of cases of deformation in both fixed and rotating frames, showing encouraging results. The model shows good agreement with DNS results for the case of pure shear flow in the presence of either transverse or streamwise mean scalar gradient, while it correctly predicts the presence of direct cascade for the passive scalar variance in two dimensional isotropic turbulence. © 2015 Elsevier Inc. 57 109 129 109-129

In this work, we revisit the coupling of the Algebraic Structure-Based Model with popular two-equation eddy viscosity models (EVM). We consider both the v2 − f model and variants of the κ-ω model. Our aim is to explore the role of the EVM in these couplings. Computations of turbulent boundary layer over a flat plate and a fully developed channel flow are initially performed for validation purposes. Then, the case of a 2D steep, smooth hill is considered, for which additional LES computations were performed in order to ascertain the validity of the experimental data. The coupling of the ASBM with the κ-ω-BSL model (hereafter called ASBMBSL) showed superior robustness when compared to the ASBM-v2- f hybrid model. Moreover, ASBM-BSL captures the size of the recirculation bubblemore accurately, and overall yields a noticeable improvement in the prediction of the turbulent statistics in the recirculation region. Allmodels fail to capture the correct shear stress profile at the top of the hill, exhibiting positive, non-realizable values near thewall. The present comparisons reveal a sensitivity of the hybrid closures to the choice of carrier model. © Springer International Publishing Switzerland 2016. 23 115 124 115-124

Understanding the multitude of factors that control pulmonary deposition is important in assessing the therapeutic or toxic effects of inhaled particles. The use of increasingly sophisticated in silico models has improved our overall understanding, but model realism remains elusive. In this work, we use Large Eddy Simulations (LES) to investigate the deposition of inhaled aerosol particles with diameters of dp=0.1,0.5,1,2.5,5 and 10μm (particle density of 1200 kg/m3). We use a reconstructed geometry of the human airways obtained via computed tomography and assess the effects of inlet flow conditions, particle size, electrostatic charge, and flowrate. While most computer simulations assume a uniform velocity at the mouth inlet, we found that using a more realistic inlet profile based on Laser Doppler Anemometry measurements resulted in enhanced deposition, mostly on the tongue. Nevertheless, flow field differences due to the inlet conditions are largely smoothed out just a short distance downstream of the mouth inlet as a result of the complex geometry. Increasing the inhalation flowrate from sedentary to activity conditions left the mean flowfield structures largely unaffected. Nevertheless, at the higher flowrates turbulent intensities persisted further downstream in the main bronchi. For dp>2.5μm, the overall Deposition Fractions (DF) increased with flowrate due to greater inertial impaction in the oropharynx. Below dp=1.0μm, the DF was largely independent of particle size it also increased with flowrate, but remained significantly lower. Electrostatic charge increased the overall DF of smaller particles by as much as sevenfold, with most of the increase located in the mouth–throat. Moreover, significant enhancement in deposition was found in the left and right lung sub-regions of our reconstructed geometry. Although there was a relatively small impact of inhalation flowrate on the deposition of charged particles for sizes dp

This work investigates by means of molecular dynamics the filling of carbon nanotubes by carbon dioxide molecules. Nanotubes of various sizes are simulated and the resulting CO2 density calculated. The effects of various CO2 models are also investigated. The results show that the carbon dioxide molecules have a natural tendency to fill the nanotubes and the final CO2 concentration inside the nanotube can be approximately 100 times (depending on diameter and CO2 model) higher than that of the external atmosphere. © 2008 Elsevier B.V. All rights reserved. 460 512 516 512-516

In this paper, the density, hydrogen bonding and self-diffusivity of water confined in carbon nanotubes are investigated. Molecular dynamics is used to simulate a large variety of nanotubes with various water models. Our results produce, for the first time, the complete trend of these properties from narrow nanotubes, where water shows particularly anomalous behaviour, to large ones where its characteristics are similar to those of bulk. 34 671 678 671-678

In this paper, the density of water confined in carbon nanotubes of different sizes and chirality is calculated. Molecular dynamics is used to simulate the spontaneous filling of the nanotube with water molecules coming from an external bath. Three H2 O filling modes are found and a correlation, which relates the density with the nanotube diameter, is proposed. © 2008 Elsevier Ltd. All rights reserved. 63 2047 2056 2047-2056

Thermal stratification and its seasonal variations in Kouris Dam in Cyprus were simulated, and the impact of five different water withdrawal schemes was studied, using the 2-D, laterally averaged CE-QUAL-W2 reservoir model. Based on the model simulations, it was found that the thermal stratification of the reservoir is significant for most of the year. Most importantly, a complete mixing of the water column, triggered by seasonal variations in meteorological conditions, occurs in late-January. Predicted thermal stratification and water temperature profiles in the reservoir are noticeably affected by water withdrawal schemes. It was found that deep-water withdrawals tend to facilitate heat transfer in the water column and deepen the water mixing layer (epilimnion), especially from September to the following January. These study results suggest that it is prudent for Kouris Dam to integrate selective water withdrawal schemes into reservoir management by using the water withdrawal effects on thermal stratification for different water quality management strategies. ABSTRACT FROM AUTHOR] Copyright of Lakes & Reservoirs: Research & Management is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) 13 51 61 51-61

Structure-based turbulence models (SBM) carry information about the turbulence structure that is needed for the prediction of complex non-equilibrium flows. SBM have been successfully used to predict a number of canonical flows, yet their adoption rate in engineering practice has been relatively low, mainly because of their departure from standard closure formulations, which hinders easy implementation in existing codes. Here, we demonstrate the coupling between the Algebraic Structure-Based Model (ASBM) and the one-equation Spalart-Allmaras (SA) model, which provides an easy route to bringing structure information in engineering turbulence closures. As the ASBM requires correct predictions of two turbulence scales, which are not taken into account in the SA model, Bradshaw relations and numerical optimizations are used to provide the turbulent kinetic energy and dissipation rate. Attention is paid to the robustness and accuracy of the hybrid model, showing encouraging results for a number of simple test cases. An ASBM module in Fortran-90 is provided along with the present paper in order to facilitate the testing of the model by interested readers. © 2014 Elsevier Inc. 52 111 128 111-128

In the current study, Large Eddy Simulations (LES) are used to investigate the transport and deposition of inhaled aerosol particles (dp = 0.1, 0.5, 1, 2.5, 5, 10 μm) in a realistic geometry of the human airways under steady inhalation. The effects of electrostatic charge and lower generation airway narrowing caused by Chronic Obstructive Pulmonary Disease (COPD) on particle transport and deposition are examined for various flowrates (sedentary - 15.2 lt/min, light - 30 lt/min and heavy activity - 60 lt/min). Results show that the mean flow structures at the three flowrates are qualitatively similar regardless of Reynolds number. Similar swirling motions are generated from the impingement of the laryngeal jet on the tracheal front wall. However, higher turbulent intensities that persist further downstream in the trachea and the main bronchi are observed as the flowrate is increased. The Deposition Efficiency (DE) of particles is increased with the flowrate due to greater inertial impaction. The majority of the larger particles are filtered in the mouththroat region, while 0.1, 0.5 and 1μm diameter particles have similar DE at a given flowrate. The effect of charge on DE of particles is more pronounced for smaller particles 1000 elementary charge units on 0.1, 0.5,1 and 2.5 μm diameter particles results in approximately 7, 3, 2.5 and 1.5 times greater overall DE than that with no charge, respectively. Obstructed lower generation airways result in enhanced deposition due to impaction caused by higher velocities in these airways. 2

In this study, we perform Direct Numerical Simulations (DNS) of fully developed turbulent flows in eccentric annuli having different diameter ratios. Annuli of unit eccentricity, and diameter ratios of 0.2591 and 0.1395 have been investigated, for a Reynolds number of 14600 based on the bulk velocity and outer wall diameter. This study aims to investigate the different flow characteristics, including the effect of the diameter ratio on the pressure gradient and the friction factor. Furthermore, this work confirms the presence of mean secondary flow for the configurations considered, while its effect on the flow characteristics and vortex structures is discussed in relation to the diameter ratios investigated. 3

Recent computational studies have shown that the airflow in the upper human airways is turbulent during much of the respiratory cycle. A feature of respiratory airflow that poses a challenge to computations based on Reynolds-Averaged Navier-Stokes (RANS) closures is the laminarturbulent-laminar transition as the flow moves from the mouth through the glottis and down to the lower conducting airways. Turbulence and unsteadiness are expected at least through the first few bifurcations of the airways. In the case of inhaled medicines, and depending on the size of the particles in the formulation, airway bifurcations are areas of preferential deposition. In this study we perform for the first time, Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) of fully developed turbulent flow through a single human airway bifurcation, emulating steady prolonged inspiration and expiration conditions. We also perform RANS simulations via the v2 - f closure model and compare with our DNS and LES results. We examine the mean flow characteristics and the turbulent vortical structures as well as their effect on the deposition of particles of different sizes. 2

Three-dimensional direct numerical simulations of a Bingham fluid flowing past a confined circular cylinder have been used in order to investigate viscoplastic effects in the wake-transition regime. The case of a cylinder confined in a plane channel with a fixed blockage ratio (ratio of the cylinder diameter to the channel height) of 0.2 has been studied, for values of the Bingham number and Reynolds numbers (based on the cylinder diameter and bulk flow velocity) in the range 0 Bn ≤ 5 and 150 ⩽ Re ⩽ 600 , respectively. The critical Reynolds number for the onset of three-dimensional flow regime has been shown to increase linearly with Bingham number, at least in the range of parameters considered. Two distinct modes of three-dimensional instability (modes A and B) have been identified in the flow, and the influence of viscoplastic effects on the evolution of these instabilities have been described. Significant deviations in the structure of the far wake from the Newtonian case have been observed and associated with a disruption of underlying processes that are known to operate in the Newtonian wake. Despite these structural differences, it has been shown that the evolution of the Strouhal number with Reynolds number in the viscoplastic fluid exhibits two discontinuous changes that are associated with the onset of the different instabilities in the flow, a behavior that mirrors the behavior in Newtonian fluids.

This paper summarizes a strategy for parallelizing a legacy Fortran 77 programusing the object-oriented (OO) and coarray features that entered Fortran in the 2003 and 2008 standards, respectively. OO programming (OOP) facilitates the construction of an extensible suite of model-verification and performance tests that drive the development. Coarray parallel programming facilitates a rapid evolution from a serial application to a parallel application capable of running on multicore processors and many-core accelerators in shared and distributed memory. We delineate 17 code modernization steps used to refactor and parallelize the program and study the resulting performance. Our initial studies were done using the Intel Fortran compiler on a 32-core shared memory server. Scaling behavior was very poor, and profile analysis using TAU showed that the bottleneck in the performance was due to our implementation of a collective, sequential summation procedure. We were able to improve the scalability and achieve nearly linear speedup by replacing the sequential summationwith a parallel, binary tree algorithm.We also tested theCray compiler, which provides its own collective summation procedure. Intel provides no collective reductions. With Cray, the program shows linear speedup even in distributed-memory execution. We anticipate similar results with other compilers once they support the new collective procedures proposed for Fortran 2015. Copyright © 2015 Hari Radhakrishnan et al. 2015

Good measures of the turbulence structure are important for turbulence modeling, flow diagnostics and analysis. Structure information is complementary to the componentality anisotropy that the Reynolds stress tensor carries, and because structures extend in space, structure information is inherently non-local. Given access to instantaneous snapshots of a turbulence field or two-point statistical correlations, one can extract the structural features of the turbulence. However, this process tends to be computationally expensive and cumbersome. Therefore, one-point statistical measures of the structural characteristics of turbulence are desirable. The turbulence structure tensors are one-point statistical descriptors of the non-local characteristics of the turbulence structure and form the mathematical framework for constructing Structure-Based Models (SBM) of turbulence. Despite the promise held by SBM, the tensors have so far been available only in a small number of DNS databases of rather simple canonical flows. This inhibits further SBM development and discourages the use of the tensors for flow analysis and diagnostics. The lack of a clear numerical recipe for computing the tensors in complex domains is one the reasons for the scarce reporting of the structure tensors in DNS databases. In particular, the imposition of proper boundary conditions in complex geometries is non-trivial. In this work, we provide for the first a time a rigorous and well-documented description of a mathematical and computational framework that can be used for the calculation of the structure tensors in arbitrary turbulent flow configurations. © 2014 Elsevier Ltd. 106 54 66 54-66

Two linear eddy-viscosity models, the v2-f and k-ω models, have been combined with an algebraic structure-based algorithm for the evaluation of the Reynolds stresses. This closure was originally designed as an integral part of the algebraic structure-based model (ASBM) to capture the turbulent anisotropy occurring in rotating wall bounded flows. It is shown that the algebraic structure-based evaluation of the Reynolds stresses can be used directly with conventional turbulence models sensitizing them to rotation. Significant improvement in the prediction of anisotropic turbulent flow can be achieved without an additional tuning of the closure coefficients. The models are evaluated in spanwise rotating channel flow and in flat plate boundary layers. The sensitivity to the Reynolds and rotation numbers is investigated. The results are compared with DNS data. © 2006 Elsevier Inc. All rights reserved. 27 653 660 653-660

We consider the case of homogeneous turbulence in a conducting fluid that is exposed to a uniform external magnetic field at low to moderate magnetic Reynolds numbers (by moderate we mean here values as high as 20). When the magnetic Reynolds number is vanishingly small (Rm ≪ 1), it is customary to simplify the governing magnetohydrodynamic (MHD) equations using what is known as the quasi-static (QS) approximation. As the magnetic Reynolds number is increased, a progressive transition between the physics described by the QS approximation and the MHD equations occurs. We show here that this intermediate regime can be described by another approximation which we call the quasi-linear (QL) approximation. For the numerical simulations performed, the predictions of the QL approximation are in good agreement with those of MHD for magnetic Reynolds number up to Rm ∼20. © 2004 Cambridge University Press. 513 199 220 199-220

The dynamics of the evolution of turbulence statistics depend on the structure of the turbulence. For example, wavenumber anisotropy in homogeneous turbulence is known to affect both the interaction between large and small scales (Kida & Hunt 1989), and the non-local effects of the pressure–strain-rate correlation in the one-point Reynolds stress equations (Reynolds 1989; Cambon et al. 1992). Good quantitative measures of turbulence structure are easy to construct using two-point or spectral data, but one-point measures are needed for the Reynolds-averaged modelling of engineering flows. Here we introduce a systematic framework for exploring the role of turbulence structure in the evolution of one-point turbulence statistics. Five one-point statistical measures of the energy-containing turbulence structure are introduced and used with direct numerical simulations to analyse the role of turbulence structure in several cases of homogeneous and inhomogeneous turbulence undergoing diverse modes of mean deformation. The one-point structure tensors are found to be useful descriptors of turbulence structure, and lead to a deeper understanding of some rather surprising observations from DNS and experiments.

This paper summarizes a strategy for parallelizing a legacy Fortran 77 program using the object-oriented (OO) and coarray features that entered Fortran in the 2003 and 2008 standards, respectively. OO programming (OOP) facilitates the construction of an extensible suite of model-verification and performance tests that drive the development. Coarray parallel programming facilitates a rapid evolution from a serial application to a parallel application capable of running on multi-core processors and many-core accelerators in shared and distributed memory. We delineate 17 code modernization steps used to refactor and parallize the program, and study the resulting performance. Our scaling studies show that the bottleneck in the performance was due to the implementation of the collective sum procedure. Replacing the sequential procedure with a binary tree procedure improved the scaling performance of the program. This bottleneck will be resolved in the future by new collective procedures in Fortran 2015. Copyright 2013 ACM. 33 40 33-40

The performance of Reynolds stress transport (RST) models in non-equilibrium flows is limited by the lack of information about two dynamically important effects: The role of energy-containing turbulence structure (dimensionality) and the breaking of reflectional symmetry due to strong mean or frame rotation. Both effects are fundamentally non-local in nature and this explains why it has been difficult to include them in one-point closures like RST models. Information about the energy-containing structure is necessary if turbulence models are to reflect differences in dynamic behavior associated with structures of different dimensionality (nearly isotropic turbulence vs turbulence with strongly organized two-dimensional structures). Information about the breaking of reflectional symmetry is important whenever mean rotation is dynamically important (flow through axisymmetric diffuser or nozzle with swirl, flow through turbomachinery, etc.). Here we present a new one-point model that incorporates the needed structure information, and show a selection of results for homogeneous and inhomogeneous flows. © 2000 Begell House Inc. Published by Elsevier Science Inc. All rights reserved. 21 599 605 599-605

In turbulence modeling, and perhaps elsewhere, one encounters the need to model a fourth-rank tensor Mijpq, which is symmetric in ij and pq, in terms of a second-rank symmetric tensor bij. It has commonly been assumed that there are fifteen linearly independent tensor forms in the most general such model. Here we show that there are only twelve, and give the three linear dependencies. © 1998 Elsevier Science Ltd. All rights reserved. 11 79 83 79-83