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A 2D aerodynamic study of the NASA&rsquo, s X-43A hypersonic aircraft is developed using two different approaches. The first one is analytical and based on the resolution of the oblique shock wave and Prandtl&ndash, Meyer expansion wave theories supported by an in-house program and considering a simplified aircraft&rsquo, s design. The second approach involves the use of a Computational Fluid Dynamics (CFD) package, OpenFOAM and the real shape of the aircraft. The aerodynamic characteristics defined as the lift and drag coefficients, the aerodynamic efficiency and the pitching moment coefficient are calculated for different angles of attack. Evaluations are made for an incident Mach number of 7 and an altitude of 30 km. For both methodologies, the required angles of attack to achieve a Vertical Force Balance (VFB) and a completely zero pitching moment conditions are considered. In addition, an analysis to optimise the nose configuration of the aircraft is performed. The mass flow rate throughout the scramjet as a function of the angle of attack is also presented in the CFD model in addition to the pressure, density, temperature and Mach fields. Before presenting the corresponding results, a comparison between the aerodynamic coefficients in terms of the angle of attack of both models is carried out in order to properly validate the CFD model. The paper clarifies the requirements needed to make sure that both oblique shock waves originating from the leading edge meet just at the scramjet inlet clarifying the advantages of fulfilling such condition.

Diffusers and the floor ahead of them create the majority of the downforce a vehicle creates. Outside motorsports, the diffuser is relatively unused, although its interaction with the ground is a consistent field of study owing to the aerodynamic benefits. The diffuser flow behavior is governed by three fluid-mechanical mechanisms: ground interaction, underbody upsweep, and diffuser upsweep. In addition, four different flow regimes appear when varying ride height, the vortices of which have great importance on downforce generation. The present study focuses on the diffuser’s fluid-dynamic characteristics undertaken within an academic framework with the objective of finding and understanding a high level of performance in these elements. Once the functioning of diffusers has been analyzed and understood, a new configuration is proposed: rear vertical airfoil endplates. The aim of the paper is to study the effect in performance of vertical airfoil endplates on diffusers in vehicle aerodynamics in a simplified geometry. The candidate to this geometry is the inversed Ahmed body, a geometry that is used as a model that simulates the flow behavior of car diffusers. Three different diffuser configurations are performed, namely 0° diffuser, 25° diffuser, and in the third case vertically installed rear vertical airfoil endplates are added to the 25° diffuser Ahmed body to change the flow field. These analyses are carried out by using open-source CFD simulation software OpenFOAM. An inlet velocity of 20 m/s is considered, as this is a typical velocity when cornering in motorsport. It is concluded that the 25° diffuser configuration generated more downforce than the 0° diffuser, which makes sense as the aim of adding a diffuser is to increase the amount of downforce produced. In addition, and as a result of the newly proposed configuration, the 25° diffuser Ahmed body with the vertical airfoil endplates emerges in a substantial increase of downforce thanks to the low-pressure zone generated at the back of the body.

This article provides a summarizing account of the results obtained in the current collabora-tive work of four research institutes concerning near-wall flow in turbomachinery. Specific questions regarding the influences of boundary layer development on blades and endwalls as well as loss mech-anisms due to secondary flow are investigated. These address skewness, periodical distortion, wake interaction and heat transfer, among others. Several test rigs with modifiable configurations are used for the experimental investigations including an axial low speed compressor, an axial high-speed wind tunnel, and an axial low-speed turbine. Approved stationary and time resolving measurements techniques are applied in combination with custom hot-film sensor-arrays. The experiments are complemented by URANS simulations, and one group focusses on turbulence-resolving simulations to elucidate the specific impact of rotation. Juxtaposing and interlacing their results the four groups provide a broad picture of the underlying phenomena, ranging from compressors to turbines, from isothermal to non-adiabatic, and from incompressible to compressible flows. The investigations reported in this article were conducted within the framework of the joint research project “Near-Wall Flow in Turbomachinery Cascades” which was funded and supported by the Deutsche Forschungsgemeinschaft (DFG) under grant number PAK 948. The responsibility for the contents of this publication lies entirely by the authors.

In this work, we study the accuracy of CFD-based data-driven models, which predict comfort-related flow parameters in a ventilated cavity with a heated floor. We compare the computational cost and accuracy of three different models, namely artificial neural network, support vector regression, and gradient boosting regression. The tested scenarios include short and long cavities with different inlet velocities. Among the studied frameworks, the artificial neural network provides the most accurate predictions for most of the tested flow configurations. However, test configurations with jet separation and a secondary vortex are more difficult to predict correctly; thus more high-fidelity data is required in order to construct a more robust and reliable model. This work is supported by the Ministerio de Economía y Competitividad, Spain [ENE2017-88697-R]. N. Morozova is supported by the by the Ministerio de Economía y Competitividad, Spain [FPU16/06333 predoctoral contract]. Part of the calculations was performed on the MareNostrum 4 supercomputer at the Barcelona Supercomputing Center [RES project IM-2021-1-0015]. The authors thankfully acknowledge these institutions.

Turbulence accounts for most of the processes in textile engineering among other interdisciplinary fields. In this chapter, a comprehensive description of turbulent models and description of important terms and theories in modeling and simulation have been exhaustively presented. Analysis of turbulent forces, model equations, description of types of turbulence models, the turbulence phenomena, and application of this concept in modeling and simulation are some of the information presented in this chapter. This chapter extensively explains the foundation of computational fluid dynamics (CFD) with practical examples of typical problems, solution strategy, implementation, and validation of algorithm. This chapter also demonstrates the application of CFD approach in machine design and modification and simulation and modeling of the ring spinning and open spinning technology. Systematic explanation of the most important concepts in turbulence modeling can be utilized to tackle numerous challenging phenomena in fluid dynamics, textile engineering, and beyond.

Computational fluid dynamics (CFD) is a reliable tool for indoor environmental applications. However, accurate CFD simulations require large computational resources, whereas significant cost reduction can lead to unreliable results. The high cost prevents CFD from becoming the primary tool for indoor environmental simulations. Nonetheless, the growth in computational power and advances in numerical algorithms provide an opportunity to use accurate and yet affordable CFD. The objective of this study is to analyze the feasibility of fast, affordable, and high-fidelity CFD simulations for indoor environment design and control using ordinary office computers. We analyze two representative test cases, which imitate common indoor airflow configurations, on a wide range of different turbulence models and discretizations methods, to meet the requirements for the computational cost, run-time, and accuracy. We consider statistically steady-state simulations for indoor environment design and transient simulations for control. Among studied turbulence models, the no-model and large-eddy simulation with staggered discretizations show the best performance. We conclude that high-fidelity CFD simulations on office computers are too slow to be used as a primary tool for indoor environment design and control. Taking into account different laws of computer growth prediction, we estimate the feasibility of high-fidelity CFD on office computers for these applications for the next decades This work is supported by the Ministerio de Economía y Competitividad, Spain [ENE2017-88697-R]. N. Morozova is supported by the by the Ministerio de Economía y Competitividad, Spain [FPU16/06333 predoctoral contract]. Part of the calculations was performed on the MareNostrum 4 supercomputer at the Barcelona Supercomputing Center [RES project I-2019-2-0021]. The authors thankfully acknowledge these institutions. The authors would also like to thank our colleague MSc Xavier Álvarez Farré for the productive discussions.

Multi-environment reactors are an innovative alternative to simplify conventional Biological Nutrient Removal (BNR) treatment trains as they are more compact and can adapt to existing quality requirements. However, maintaining the desired environmental conditions in different zones of the reactor implies the need for deflectors or mixing devices that generate a complex hydrodynamic behaviour. Therefore, to ensure the desired biological efficiency, hydraulic optimization is essential. For that purpose, a hydrodynamic optimization methodology combining Computational Fluid Dynamics (CFD) and dimensional analysis is developed and presented in this work. The methodology is applied to AnoxAn, an anaerobic-anoxic reactor for BNR. The CFD model is constructed using the OpenFOAM® open source toolbox and has been already validated in a previous work by the authors. Different features as hydraulic separation, dead volumes, short-circuiting or mixing performance are evaluated and main results show that configurations of AnoxAn with high slenderness have the most efficient hydrodynamic behaviour. R. Blanco-Aguilera is indebted to the MEC (Ministerio de Educación, Cultura y Deporte, Spain) for the funding provided in the FPU (Formación del Profesorado Universitario) Grant Program (FPU16-05036). We acknowledge Santander Supercomputación support group at the University of Cantabria who provided access to the supercomputer Altamira Supercomputer at the Institute of Physics of Cantabria (IFCA-CSIC), member of the Spanish Supercomputing Network, for performing simulations.

The dual coolant lithium lead (DCLL) is a candidate to be an effective breeding blanket (BB) concept for nuclear fusion technologies. One critical point of this design is the magnetohydrodynamic (MHD) effects involving Lorentz damping force which produces relevant pressure drop in the eutectic flow. In the framework of the European DEMO, the application of sandwich-like steel-alumina-steel Flow Channel Insert (FCI) seems to be the best solution to reduce the pressure drop by electrically decoupling the liquid PbLi from the Eurofer walls. The impact of the FCI on the PbLi velocity profile is analyzed in this work with a CFD solver implemented on OpenFOAM. Under the assumption of non-buoyant fully developed channel flow the temperature map in the channel is computed. Based on the temperature field, the induced deformation is evaluated. The effects of the FCI deformation and possible rupture of the FCI on the velocity profile and on the corresponding pressure drop are then parametrically investigated. Results show that the deformation of the FCI and the possible break in the Hartmann wall do not lead to significant variations in the pressure drop from the case of intact FCI in a wide range of interaction parameters.

This paper presents a three-dimensional numerical study of the bubble generation process in a micro T-junction, performed with the commercial computational fluid dynamics solver ANSYS Fluent, version 15.0.7. Numerical results on the bubble generation frequency, bubble velocity, volume void fraction, bubble volume, and characteristic bubble lengths are compared with experimental data. Additionally, a new simple fitting for the bubble generation frequency, based upon previously reported experimental works, is proposed here.

In this work, we study the transition from squeezing to dripping during the formation of bubbles in a capillary T-junction in conditions relevant to microgravity. The junction is formed by two perpendicular cylinders of equal section (1 mm of internal diameter). The capillary number Ca (based on the continuous phase) is used as the key parameter of the study. For the range of Ca covered in this paper, the same two common bubble formation mechanisms as the ones described in the related literature have been observed: squeezing regime at low Ca and dripping regime for higher Ca. This paper provides a new value of the critical Ca for the transition from squeezing to dripping. This value has been obtained with two independent approaches, experimentally and numerically. Experimental photographs have been used to determine the value of Ca at which a gap appears between the forming bubble and the capillary’s wall, as an evidence of the activation of the shearing mechanism related to the dripping regime. Additionally, the dependence of the bubble volume on the capillary number and the gas/liquid flow rate ratio has been analysed. In this work, we also propose a new numerical approach, complementary to the experimental one, carried out with the Computational Fluid Dynamics solver ANSYS Fluent v15.0.7. Numerical simulations have been performed to study the geometry and the behaviour of the gas-liquid interface during the cycle of bubble formation. Upstream the T-junction, as the fluctuation in pressure decreases, the vertical movement of the rear meniscus (gas-liquid interface in contact with the solid vertical capillary) also decreases, and the shear stresses begins to play an active role until overcoming the squeezing mechanism. Numerical simulations presented in this paper support the experimental observations, confirming that Computational Fluid Dynamics studies can be a useful tool to improve the experimental knowledge.

Abnormal fluid dynamics at the ascending aorta may be at the origin of aortic aneurysms. This study was aimed at comparing the performance of computational fluid dynamics (CFD) and fluid–structure interaction (FSI) simulations against four-dimensional (4D) flow magnetic resonance imaging (MRI) data; and to assess the capacity of advanced fluid dynamics markers to stratify aneurysm progression risk. Eight Marfan syndrome (MFS) patients, four with stable and four with dilating aneurysms of the proximal aorta, and four healthy controls were studied. FSI and CFD simulations were performed with MRI-derived geometry, inlet velocity field and Young's modulus. Flow displacement, jet angle and maximum velocity evaluated from FSI and CFD simulations were compared to 4D flow MRI data. A dimensionless parameter, the shear stress ratio (SSR), was evaluated from FSI and CFD simulations and assessed as potential correlate of aneurysm progression. FSI simulations successfully matched MRI data regarding descending to ascending aorta flow rates (R2 = 0.92) and pulse wave velocity (R2 = 0.99). Compared to CFD, FSI simulations showed significantly lower percentage errors in ascending and descending aorta in flow displacement (−46% ascending, −41% descending), jet angle (−28% ascending, −50% descending) and maximum velocity (−37% ascending, −34% descending) with respect to 4D flow MRI. FSI- but not CFD-derived SSR differentiated between stable and dilating MFS patients. Fluid dynamic simulations of the thoracic aorta require fluid–solid interaction to properly reproduce complex haemodynamics. FSI- but not CFD-derived SSR could help stratifying MFS patients. This study was funded by Ministerio de Economía y Competitividad (grant no. RTC-2016-5152-1), Fundació la Marató de TV3 (grant no. 20151330), FP7 People: Marie-Curie Actions (grant no. 267128), Instituto de Salud Carlos III (grant nos PI14/0106 and PI17/00381) and ‘la Caixa’ Foundation. M.V. was funded by CompBioMed2, grant agreement ID: 823712, funded under: H2020-EU.1.4.1.3; and SILICOFCM, grant agreement ID: 777204, funded under: H2020-EU.3.1.5.

In this work, a new model for the analysis of incompressible fluid flows with massive instabilities at different scales is presented. It relies on resolving all the instabilities at all scales without any additional model, i.e., following the direct numerical simulation style. Nevertheless, the computation is carried out at two levels or scales, termed the coarse and the fine. The fine-scale simulation is performed on representative volume elements providing the homogenized stress tensor as a function of several dimensionless numbers characterizing the flow. Consequently, the effect of the fine-scale instabilities is transferred to the coarse level as a homogenized stress tensor, a procedure inspired by standard multi-scale methods used in solids. The present proposal introduces a new way for the treatment of the flow at the fine scale, simulating not only the coarse scale but also the fine scale with all the necessary detail, but without incurring in the excessive computational cost of the classical DNS. Another interesting aspect of the present proposal is the use of a Lagrangian formulation for convecting the eddies simulated on the fine mesh through the coarse domain. Several examples showing the potentiality of this methodology for the simulation of homogeneous flows are presented. Fil: Idelsohn, Sergio Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina. International Center for Numerical Methods in Engineering; España Fil: Nigro, Norberto Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Larreteguy, Axel Eduardo. Universidad Argentina de la Empresa; Argentina Fil: Gimenez, Juan Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina Fil: Ryzhakov, Pavel. Centre Internacional de Mètodes Numèrics En Enginyeria(cimne); España

Air quality in major cities is reaching worrisome levels across the planet owing to large-scale industrialization. As a result, air purification systems are becoming a fertile and emerging field for research. Here, consideration is given to the use of a small-medium scale air purification system for cities using a kind of solar thermal panels by inducing local convective currents intended to be used in parks, housing estates, or similar urban places providing a local improvement of the quality of the air. The main difficulty which arose when attempting to use these convective currents is that the upward flow of hot air, which has been cleaned from contaminant particles during its upward travel, must be returned back to the ground. To accomplish this, air must be cooled during the travel in order to obtain an effective buoyancy. Several possible solutions have been proposed in the past, for example, the use of a dedicated cooling system as is the use of water spraying systems which could be an attractive option for large towers. However, for small-medium scale air cleaners, dedicated spraying cooling systems are out of question either because of the requirement of water flow or because of the high local humidity generated which can be uncomfortable for humans. One possible solution could be taking advantage of vertical panels in which a side of the panel is permanently irradiated and the other is permanently in the shadow; in this way, heating and cooling could be performed eliminating the need for specialized cooling systems, and although the effective buoyancy—and then the purified air mass flow—of such a system is considerably reduced, nevertheless, it could still be acceptable for local small-scale applications. Utilizing a simplified physical model, the effective buoyancy and attainable air mass flow were calculated. It is shown that for a small panel of 5 m-height or thereabouts, an air flow per unit of width ∼0.4 kg/s is attainable, and for a 10 m-height panel, an air flow per unit of width 0.6 kg/s is attainable. Computational fluid dynamics simulations were performed which agree with the analytical results within ±30 %.

The suspensions used in heavy vehicles often consist of several oil and two gas chambers. In order to perform an analytical study of the mass flow transferred between two gas chambers separated by a nozzle, and when considering the gas as compressible and real, it is usually needed to determine the discharge coefficient of the nozzle. The nozzle configuration analyzed in the present study consists of a T shape, and it is used to separate two nitrogen chambers employed in heavy vehicle suspensions. In the present study, under compressible dynamic real flow conditions and at operating pressures, discharge coefficients were determined based on experimental data. A test rig was constructed for this purpose, and air was used as working fluid. The study clarifies that discharge coefficients for the T shape nozzle studied not only depend on the pressure gradient between chambers but also on the flow direction. Computational Fluid Dynamic (CFD) simulations, using air as working fluid and when flowing in both nozzle directions, were undertaken, as well, and the fluid was considered as compressible and ideal. The CFD results deeply helped in understanding why the dynamic discharge coefficients were dependent on both the pressure ratio and flow direction, clarifying at which nozzle location, and for how long, chocked flow was to be expected. Experimentally-based results were compared with the CFD ones, validating both the experimental procedure and numerical methodologies presented. The information gathered in the present study is aimed to be used to mathematically characterize the dynamic performance of a real suspension IM-2020-1-0001 Optimization of five Active Flow Control parameters on a SD7003 wing profile at several angles of attack from 4 to 16 and at Reynolds number 60000 (second period)

The high complexity of current Formula One aerodynamics has raised the question of whether an urgent modification in the existing aerodynamic package is required. The present study is based on the evaluation and quantification of the aerodynamic performance on a 2017 spec. adapted Formula 1 car (the latest major aerodynamic update) by means of Computational Fluid Dynamics (CFD) analysis in order to argue whether the 2022 changes in the regulations are justified in terms of aerodynamic necessities. Both free stream and flow disturbance (wake effects) conditions are evaluated in order to study and quantify the effects that the wake may cause on the latter case. The problem is solved by performing different CFD simulations using the OpenFoam solver. The significance and originality of the research may dictate the guidelines towards an overall improvement of the category and it may set a precedent on how to model racing car aerodynamics. The studied behaviour suggests that modern F1 cars are designed and well optimised to run under free stream flows, but they experience drastic aerodynamic losses (ranging from −23% to 62% in downforce coefficients) when running under wake flows. Although the overall aerodynamic loads are reduced, there is a fuel efficiency improvement as the power that is required to overcome the drag is smaller. The modern performance of Ground Effect by means of vortices management represent a very unique and complex way of modelling modern aerodynamics, but at the same time notably compromises the performance of the cars when an overtaking maneuver is intended.

One of the main advantages of fluidic oscillators is that they do not have moving parts, which brings high reliability whenever being used in real applications. To use these devices in real applications, it is necessary to evaluate their performance, since each application requires a particular injected fluid momentum and frequency. In this paper, the performance of a given fluidic oscillator is evaluated at different Reynolds numbers via a 3D-computational fluid dynamics (CFD) analysis. The net momentum applied to the incoming jet is compared with the dynamic maximum stagnation pressure in the mixing chamber, to the dynamic output mass flow, to the dynamic feedback channels mass flow, to the pressure acting to both feedback channels outlets, and to the mixing chamber inlet jet oscillation angle. A perfect correlation between these parameters is obtained, therefore indicating the oscillation is triggered by the pressure momentum term applied to the jet at the feedback channels outlets. The paper proves that the stagnation pressure fluctuations appearing at the mixing chamber inclined walls are responsible for the pressure momentum term acting at the feedback channels outlets. Until now it was thought that the oscillations were driven by the mass flow flowing along the feedback channels, however in this paper it is proved that the oscillations are pressure driven. The peak to peak stagnation pressure fluctuations increase with increasing Reynolds number, and so does the pressure momentum term acting onto the mixing chamber inlet incoming jet.

The rapidly growing computational capacity hasmade CFD simulations an attractive tool for indoorenvironmental applications. The ability of CFD toperform transient simulations could be incorporatedinto model predictive control systems for buildings inorder to correctly reproduce prompt disturbances inthe air field, such as opening doors and windows orchanges in occupants behaviour. In this work, twocharacteristic configurations which mimic typical air-flow patterns inside buildings are studied using dif-ferent grid sizes and turbulence models. Case one isa tall turbulent differentially heated cavity and casetwo is the turbulent mixed convection in a ventilatedsquare cavity. The Spearman’s rank correlation coef-ficient for transient simulations is compared againstcomputational time for different CFD approaches,and the possibility of performing real-time simula-tions is evaluated. Among different turbulence mod-els studied, the no-model approach with symmetrypreserving discretization has shown the best overallperformance in terms of computational cost and ac-curacy of the results.

Concentrated solar power technologies are gaining more attention in the last two decades in order to replace the conventional power technologies and reduce their environmental impact. Among the developed concentrating technologies, parabolic trough solar collector and solar tower are the most mature and dominant technologies. As part of the continuous development of these technologies, significant efforts have been deployed to predict and improve their performance, and therefore reduce their cost and make them more competitive. In this context, numerous analytical and numerical studies have been developed and presented in the literature. This review aims to summarize the state-of-the-art modeling approaches used to simulate, predict and evaluate the optical, thermal and dynamic performance of high-temperature solar thermal collectors. The review includes the different analytical and ray tracing models used to determine the non-uniform flux on the receiver aperture. Energy balance models are also presented as simple and easy computational models suitable to predict the thermal performance at a reasonable time and computational cost, whereas Computational Fluid Dynamic models are more convenient to study the details of the coupled fluid flow and heat transfer in the internal and external flow. The review also includes dynamic models such as the lumped capacitance models which are used to simulate the dynamic characteristics of the heat transfer fluid and interaction with the solar receiver under transient conditions. The dynamic behavior of the whole solar plant using different codes is examined. Furthermore, different features and capabilities of those approaches are also analyzed and compared. Finally, the use of numerical modeling in the development of new designs and assessment of the use of nanofluids is discussed. In summary, this work presents a comprehensive review of the existing numerical models and could serve as a guideline to develop new models for future trends in concentrating solar technologies.

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].

It is well known that hydrodynamic drag reduction can be obtained by locally surround-ing an immersed solid boundary with another low viscosity-fluid resulting in a lubricating effect. In aerodynamics propulsion, this principle has been used in the so called super-cavitation, in which the viscous drag resistance acting on a, say, torpedo or submarine is substantially reduced by enclosing the body in a low-viscosity gas bubble. In this paper we are exploring the same idea but in an opposite direction, namely: we want to know if creating a high-viscosity fluid layer or film can result in an anti-lubricating effect in which the viscous drag resistance is substantially increased, i.e., a drag enhancement technique. The main motivation behind this idea is in application to the Red planet for landing large payloads as for example in future human missions with payloads several factors larger than an unmanned spacecraft and where the thin atmosphere of Mars sharply reduce the aerobraking capabilities. Utilizing a simplified turbulent layer model the theoretical justification of this rather intuitive idea is outlined. Some preliminary computational fluid dynamics calculations were performed which encourage further research.

To increase renewable energy generation in some hydroelectric dams, a solution consisting in installing wind turbines close to dams is proposed. Indeed, dam surroundings are prone to benefit from wind speed-up effect, extra wind generation associated with thermal winds, and existing electrical infrastructure. Identifying the most suitable locations for turbines, that is, areas of relatively high-speed and low-turbulence wind, is fundamental to maximize this complementary power. Easy accessibility to turbines and minimum distance to dam electrical infrastructure are also essential to reduce the costs. Thus, a methodology is proposed to improve wind resource assessment in complex mountainous areas. First, potentially interesting dams are chosen using statistical local wind data. Second, weighted results of wind speed and turbulence intensity, considering all wind directions are presented based on CFD simulations. Finally, wind power density and annual energy production maps are generated, along with accessibility maps, to identify suitable sites. The Camarasa dam in the north-east of the Iberian Peninsula is chosen as case study to show and test the proposed methodology. Error estimations are provided, along with validation against Wind Atlas data and WAsP simulations.

A double acting cylinder operation has been fully monitored in its key functional parameters, focused on characterization of end-of-stroke cushioning and starting phases. Being the cylinder performance reliant in the piston constructive geometry, the number and location of piston circumferential grooves is a significant parameter affecting the internal cushioning system performance. An eddy current displacement sensor assembled in the piston allows assessment of piston radial displacement inside the cylinder tube, which is directly related with the studied operating phases. Due to such 3D displacements, the piston becomes as an active and self-adjusting element along the functional cycle of the cylinder. Mechanical joints orientation and operating pressure are also relevant parameters affecting piston radial displacement and, thus, the cushioning and starting performance. Computational Fluid Dynamics (CFD) results confirm the observed functional role of the perimeter grooves; the flow and pressure distributions, where develops a significant radial force, are also in accordance with the registered radial displacement.

The response of an elastic membrane to an external flow and its significance with regard to aerodynamic drag enhancement technique is discussed. It is shown that because the response of an elastic membrane to an external flow and the development of Kelvin-Helmholtz instabilities due to the relative motion between the atmosphere and the spacecraft, the flapping of the membrane will translate in a ulsating pressure onto the walls which added to the skin drag friction will increase the apparent drag force exerted by the surrounding media, i.e, a drag enhancement technique. Utilizing a simplified linear and inviscid stability analysis an estimate for the response of the membrane as well as the drag enhancement was obtained. The technique could be particularly interesting for descent spacecraft vehicles in planets with reduced atmosphere as Mars.

In this paper, numerical simulations of lubricating grease flow in the grease pocket of a double restriction seal geometry using computational fluid dynamics are presented. The grease is treated as a single-phase Herschel–Bulkley fluid with different rheological properties corresponding to NLGI grade 00, 1 and 2. The numerical code and rheology model have been validated with a semi-analytical solution based on flow measurements using microparticle image velocimetry. The flow has been modelled for low and high rotational speeds driving the flow, and elevated temperatures. Also, the evolution of contaminant particles in the grease pocket is investigated. It was found that the flow and velocity distribution in the pocket—and consequently the contaminant particle concentration evolution, is characterized by the shear thinning rheology of the grease. With higher shear rates in the grease and higher temperatures, the grease approaches a more Newtonian type of behaviour leading to a reduced yield and shear thinning characteristics directly affecting the grease ability to transport contaminant particles.

Since 2011, the European project Mont-Blanc has been focused on enabling ARM-based technology for HPC, developing both hardware platforms and system software. The latest Mont-Blanc prototypes use system-on-chip (SoC) devices that combine a CPU and a GPU sharing a common main memory. Specific developments of parallel computing software and well-suited implementation approaches are of crucial importance for such a heterogeneous architecture in order to efficiently exploit its potential. This paper is devoted to the optimizations carried out in the TermoFluids CFD code to efficiently run it on the Mont-Blanc system. The underlying numerical method is based on an unstructured finite-volume discretization of the Navier–Stokes equations for the numerical simulation of incompressible turbulent flows. It is implemented using a portable and modular operational approach based on a minimal set of linear algebra operations. An architecture-specific heterogeneous multilevel MPI+OpenMP+OpenCL implementation of such kernels is proposed. It includes optimizations of the storage formats, dynamic load balancing between the CPU and GPU devices and hiding of communication overheads by overlapping computations and data transfers. A detailed performance study shows time reductions of up to on the kernels’ execution with the new heterogeneous implementation, its scalability on up to 128 Mont-Blanc nodes and the energy savings (around ) achieved with the Mont-Blanc system versus the high-end hybrid supercomputer MinoTauro. The research leading to these results has received funding from the European Community’s Seventh Framework Programme [FP7/2007–2013] and Horizon 2020 under the Mont-Blanc Project (www.montblanc-project.eu), grant agreement n 288777, 610402 and 671697. The work has been financially supported by the Ministerio de Ciencia e Innovación, Spain (ENE- 2014-60577-R), the Russian Science Foundation, project 15-11-30039, CONICYT Becas Chile Doctorado 2012, the Juan de la Cierva posdoctoral grant (IJCI-2014-21034), and the Initial Training Network SEDITRANS (GA number: 607394), implemented within the 7th Framework Programme of the European Commission under call FP7-PEOPLE- 2013-ITN. Our calculations have been performed on the resources of the Barcelona Supercomputing Center. The authors thankfully acknowledge these institutions.

This paper presents some recent efforts carried out on the expansion of the scalability of TermoFluids multi-physics Computational Fluid Dynamics (CFD) code, aiming to achieve petascale capacity for a single simulation. We describe different aspects that we have improved in our code in order to efficiently run it on 131,072 CPU-cores. This work has been developed using the BlueGene/Q Mira supercomputer of the Argonne Leadership Computing Facility, where we have obtained feedback at the targeted scale. In summary, this is a practical paper showing our experience at reaching the petascale paradigm for a single simulation with TermoFluids.

A new parallel method for simulations with non-overlapping disconnected mesh domains but adjacent boundaries is presented and studied. This technique allows simulations using 3D unstructured meshes that are independent.

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0). Cushioning is an important aspect in hydraulic cylinder performance. The piston has to be decelerated before it strikes the end cap in order to avoid stresses in the cylinder components and reduce vibration that can be transmitted to the machine. One of the least-studied methods is internal cushioning by grooves in the piston. In this method, the flow is throttled with adequately designed grooves when the piston reaches the outlet port position. The purpose of the present work is to present a method to estimate the pressure-drop coefficients for a certain design of piston grooves in order to provide a model to develop a dynamic system simulation of the cushion system. The method is based on a computational fluid dynamic simulation of flow through piston grooves to the outlet port for each piston’s static position. The results are compared with experimental measurements, and a correction, based on Reynolds number, is proposed. Good agreement, below 16%, was obtained for all the positions but particularly for the last grooves, for which the numerical result’s deviation to the experimental measurements was less than 10%. In general, the numerical simulation tended to underestimate the pressure drop for the first grooves and overestimate the calculation for the last grooves.

The numerical analysis of an external gear pump with cavitation effects has been validated with experimental data obtained by applying Time-Resolved Particle Image Velocimetry. The effect of inlet and outlet pressure on volumetric efficiency has been studied numerically. First, the Particle Image Velocimetry method was used to analyze the two-dimensional velocity field in the middle plane of the suction chamber of the gear pump. The main improvement, with respect to previous similar analysis is the use of alginate micro particles as tracers. It is seen that the two-dimensional model is able to characterize the flow field of the real pump in the region of the inlet chamber in which cavitation is expected. In a previous study, it was seen that a cavitation cloud acted as a virtual contact point at low pressure, being responsible for an increase on the volumetric efficiency. The first set of simulations represents the pump working with high outlet pressure. Now, the cavitation cloud is not present and cavitation no longer helps to improve the efficiency of the pump. The second set of simulations represents the pump with an inlet loss factor, which implies a mean inlet pressure below atmospheric conditions. This allows cavitation clouds to propagate upstream. Despite the larger cavitation clouds, volumetric efficiency only drops at high operating velocities, when some clouds become trapped between gears and casing and are transported to the pressure side.

The flow over triangular-shaped cliffs is studied through Computational Fluid Dynamics simulations, using the RANS approach closed with the SST turbulence model. The formation of tip-vortices on the sides of the cliff is studied, taking into account the influence of the cliff geometry and the incoming wind. CFD results are compared with experimental data on 2D planes located above the cliff. Good agreement between the two is obtained once small experimental deviations from the nominal cliff geometry are accounted for in the simulations. In addition, 3D results, such as visualization of the vortices, allow a better understanding of the complex flow over such geometry to be achieved.

A mixture fraction formulation to perform direct numerical simulations of a disperse and dilute two-phase system consisting of water liquid and vapor in air in local thermodynamic equilibrium using a two fluid model is derived and discussed. The goal is to understand the assumptions intrinsic to this simplified but commonly employed approach for the study of two-layer buoyancy reversing systems like the cloud-top mixing layer. Emphasis is placed on molecular transport phenomena. In particular, a formulation is proposed that recovers the actual non diffusive liquid-phase continuum as a limiting case of differential diffusion. High-order numerical schemes suitable for direct numerical simulations in the compressible and Boussinesq limits are described, and simulations are presented to validate the incompressible approach. As expected, the Boussinesq approximation provides an accurate and efficient description of the flow on the scales (of the order of meters) that are considered.

The aim of this paper is twofold. First, it is difficult for a newcomer in the NumericalWeather Prediction (NWP) community to find similarities with Computational Fluid Dy-namics (CFD) techniques as far as the numerical methods of the dynamical cores in NWPare concerned. Different variables than the CFD traditional conservative one are used andseemingly different discretization techniques have been developed, whereas the very sameEuler equations are being solved in both cases. So the first aim is to compare and contrastthe main numerical elements used in both communities. The second aim consists in val-idating a CFD solver adapted to NWP to a set of traditional NWP benchmarks on fullynonstructured three dimensional configurations. It is shown that it produces accurate andlow diffusive results. The main advantages of this approach are the same than comparedto CFD finite difference solvers, namely scalability, adaptivity for localized phenomenaand geometrical flexibility. Pole singularities are trivially removed. Keywords: Numeri-cal Weather Prediction, Computational Fluid Dynamics, compressible explicit edge-basedHLLC solver, density current, gravity waves

Management and follow-up of chronic aortic dissections continues to be a clinical challenge due to progressive aortic dilatation. To predict dilatation, guidelines suggest follow-up of the aortic diameter. However, dilatation is triggered by haemodynamic parameters (pressure and wall shear stresses (WSS)), and geometry of false (FL) and true lumen (TL). We aimed at a better understanding of TL and FL haemodynamics by performing in-silico (CFD) and in-vitro studies on an idealized dissected aorta and compared this to a typical patient. We observed an increase in diastolic pressure and wall stress in the FL and the presence of diastolic retrograde flow. The inflow jet increased WSS at the proximal FL while a large variability in WSS was induced distally, all being risk factors for wall weakening. In-silico, in-vitro and in-vivo findings were very similar and complementary, showing that their combination can help in a more integrated and extensive assessment of aortic dissections, improving understanding of the haemodynamic conditions and related clinical evolution.

© 2018 WIT Press In this work, a numerical framework for the direct numerical simulation of tsunami waves generated by landslide events is proposed. The method, implemented on the TermoFluids numerical platform, adopts a free surface model for the simulation of momentum equations; thus, considering the effect of air on the flow physics negligible. The effect of the solid motion on the flow is taken into account by means of a direct forcing immersed boundary method (IBM). The method is available for 3-D unstructured meshes; however, it can be integrated with an adaptive mesh refinement (AMR) tool to dynamically increase the local definition of the mesh in the vicinity of the interfaces, which separate the phases or in the presence of vortical structures. The method is firstly validated by simulating the entrance of objects into still water surfaces for 2-D and 3-D configurations. Next, the case of tsunami generation from a subaerial landslide is studied and the results are validated by comparison to experimental and numerical measurements. Overall, the model demonstrates its efficiency in the simulation of this type of physics, and a wide versatility in the choice of the domain discretization.

The application of a new finite element (FE) technique for the solution of stratified,non-hydrostatic, low-Mach number flows is introduced in the context of mesoscale atmo-spheric modeling. In this framework, a Compressible Variational Multiscale (VMS-C)finite element algorithm to solve the conservative form of the Euler equations coupled tothe conservation of potential temperature was developed. Thismethodologyisnewinthefields of Computational Fluid Dynamics for compressible flows and in Numerical WeatherPrediction (NWP), and we mean to show its ability to maintain stability in the solution ofthermal, gravity-driven flows in a stratified environment. This effort is justified by the ad-vantages offered by a Galerkin finite element algorithm when m assive parallel efficiency is aconstraint, which is indeed becoming the paradigm for both CFD and NWP practitioners.The algorithm is validated against the standard test cases specifically designed to test thedynamical core of new atmospheric models. In the context of buoyantandgravityflowsthree tests are selected among those presented in the literature: the warm rising smoothanomaly, and two versions of the density current evolution from a cold disturbance definedby different initial conditions. The reference quantitative andqualitativevaluesaretakenfrom the literature and from the output obtained with the Weather Research and Forecastingmodel (WRF-ARW), a state-of-the-art research NWP model.Keywords: Numerical Weather Prediction, Low Mach, Compressible Flows, High Perfor-mance Computing

Considering that the most common reason for electronic component failure is the excessive temperature level, an efficient thermal management design can prolong the operating life of the equipment, while also increasing its performance. Computational Fluid Dynamics and Heat Transfer (CFD&HT) have proved valuable in the study of these problems, since they can produce reliable fields of fluid flow, temperature and heat fluxes. Moreover, thanks to the recent advances in high-performance computers, CFD&HT numerical simulations are becoming viable tools to study real problems. The conventional approach, which consists of employing body-conformal meshes to the solids and fluids regions, often results costly and ineffective in applications with very complex geometries and large deformation. For these cases, an alternative approach, the Immersed Boundary Method (IBM), which employs a non-body conformal mesh and discretizes the entire domain using a special treatment in the vicinity of the solid-fluid interfaces, has proven more effective. In this work, an IBM was extended to simulate problems with conjugate heat transfer (CHT) boundary conditions taking into account the radiative exchange between surfaces. It was designed to work with any type of mesh (domain discretization) and to handle any body geometry. The implementation was validated and verified by several simulations of benchmark cases. Moreover, the IBM was applied in an industrial application which consists of the simulation of a Smart Antenna Module (SAM). All in all, the carried out studies resulted in a monolithic methodology for the simulation of realistic situations, where all three heat transfer mechanisms can be considered in complex geometries.

© 2018. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ Numerical simulations are carried out on the flow over a realistic generic car geometry, the DrivAer-fastback car model. Pure large eddy simulations (LES) and wall-modeled large eddy simulations (WMLES) are used and compared to numerical and experimental results to assess the validity of these approaches when solving the flow field around complex automotive geometries. Results show a 70% CPU time reduction when using the wall model. Drag coefficient results show the influence of the wall model on coarser meshes is positive, reducing the difference on those obtained using finer meshes. Pressure profiles exhibit mixed results. The wall model used works well in adverse pressure gradients and smooth geometry changes. Results worsen in sections where the flow detaches and experiences large pressure drops. Flow structures and unsteady effects around the car are also analyzed, obtaining several characteristic frequencies for the different flow structures encountered. It should be noted that the present investigation shows how WMLES helps to reduce the computing cost and response vs pure LES, while providing high-quality unsteady data, although computational cost remains high. Results show potential in the introduction of this tool as a competitive simulation strategy for complex geometries.

Runner and distributor blockages in hydraulic turbines occur due to the ingestion of external bodies such as rocks or logs. These obstructions can change the amplitude and uniformity of the pressure pulsations in the machine, creating large unbalanced forces that can lead to reduced efficiency, increased vibration and mechanical damage. In this paper, the effects of obstructions caused by ingested bodies in the runner and the distributor of a pump turbine on its internal pressure pulsation were investigated by means of computational fluid dynamics. A numerical model of an unobstructed pump turbine is presented and validated against experimental data. Several cases of runner or distributor blockage were studied, and their RSI pressure pulsations were recorded and analyzed at different locations. The results obtained allow us to characterize the effect of these blockages on the machine’s RSI, which can be helpful for the correct diagnosis of these types of damage.