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Treballs Finals de Grau d'Enginyeria Biomèdica. Facultat de Medicina i Ciències de la Salut. Universitat de Barcelona. Curs: 2022-2023. Tutor/Director: Comelles Pujadas, Jordi, Cell migration plays a crucial role in various physiological and pathological processes, including immune response and cancer metastasis. The complex interplay of the cancer cells with the microenvironment and the immune cell recruitment has emerged as a critical aspect in the progression of colorectal cancer. Cytotoxic T lymphocytes infiltrate the tumour microenvironment to exert anti-tumour immunity. To get to the tumour stroma, cells have to extravasate the vascular endothelial barrier in a process called transendothelial migration. We herein develop a microfluidic device capable of investigating the migration of T cells within an environment that closely mimics In vivo tissue characteristics. We have developed different protocols to fabricate microchannels of two different materials, polydimethylsiloxane, and polyacrylamide. Photolithography and novel microfabrication techniques have been employed to acquire confined microchannels. The microchannels successfully recreated key aspects of In vivo environment, enabling precise control of size and confinement. We have studied and confirmed the advantages of using hydrogels in microfluidics and their tuneable mechanical properties have been proved. Finally, the PDMS microfluidic chip has been tested with Jurkat cells and we have confirmed the suitability of the device for studying T cell migration profiles.

In this work, consideration is given to thermal contraction of the boundary layer from the progressive cooling of the airfoil and its possible technological use as an active flow control technique. Here, it is thought that if the airfoil is progressively cooled from the leading-edge toward the trailing-edge the increase in density will translate into a progressive contraction of the boundary layer which eventually could be used as technique for either re-attachment or delay detachment of the boundary layer. Utilizing the von Karman momentum integral an analytical expression for the reduction of the thickness of the boundary layer by thermal contraction was derived which predicts contractions around 10 percent for temperatures drops around 50° K. Experimental measurements made on a heated flat plate with controlled thermal gradient agree with the theoretical prediction within a 10 per cent. The possibility of prompt contraction of the boundary layer by condensation (of the air or its moisture content) if the temperature drops below the subcooling temperature, is an open question which should be addressed in future research

The topology of multiscale turbulent motions in a high-pressure transcritical channel flow is studied using direct numerical simulations. In particular, the system analyzed corresponds to high-pressure (P/Pc=2) microconfined turbulence of N2 at transcritical conditions imposed by a temperature difference between the cold (T/Tc=0.75) and hot (T/Tc=1.5) walls for a friction Reynolds number of Ret=100 (cold wall). The invariants of the velocity-gradient, rate-of-strain, and rate-of-rotation tensors are computed at different length scales. The joint probability density functions of the invariants are calculated and conditioned based on the distance from the walls and additionally compared against an equivalent low-pressure case at isothermal conditions. The results indicate that the presence of higher levels of vorticity close to the hot wall significantly impacts the flow topologies in the viscous sublayer. As a result, topology distributions of the velocity-gradient tensor typical from the outer region are observed in the vicinity of the hot wall. Moreover, the second invariants of the rate-of-strain and rate-of-rotation tensors indicate a large probability of vortex sheet events in the hot (supercritical gaslike) region. Finally, at lengths comparable to the density gradient scale, the presence of vortex sheet structures is diminished with respect to the reference low-pressure case to favor more tubelike flow motions. As inferred from the vorticity transport equation, this behavior is connected to the appearance of a baroclinic-type instability generated from the combination of the external force driving the flow and the large variation of density across the pseudoboiling region. This work is funded by the European Union (ERC, SCRAMBLE, Grant No. 101040379). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. The authors also acknowledge support from the Beatriz Galindo program (Distinguished Researcher, Grant No. BGP18/00026) of the Ministerio de Ciencia, Innovación y Universidades (Spain), the SRG program (Grant No. 2021-SGR-01045) of the Generalitat de Catalunya (Spain), and the computer resources at FinisTerrae III and the technical support provided by CESGA (Grant No. RES-IM-2023-1-0005).

Stably stratified Taylor–Couette flow has attracted much attention due to its relevance as a canonical example of the interplay among rotation, stable stratification, shear and container boundaries, as well as its potential applications in geophysics and astrophysics. In this article, we review the current knowledge on this topic, highlight unanswered questions and propose directions for future research. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper (part 2)’.

Common methods for hold-up time and volume determination in Reversed-Phase Liquid Chromatography (RPLC) have been tested for Hydrophilic Interaction Liquid Chromatography (HILIC). A zwitterionic ZIC-HILIC column has been used for the testing. The pycnometric determination method, based on differences in column weight when filled with water or organic solvent, provides the overall volume of solvent inside the column. This includes the volume of eluent semi-sorbed on the packing of the column, which acts as the main stationary phase. The homologous series approach, based on the retention behavior of homologues in relation to their molecular volume, allows the determination of accurate hold-up volumes. However, the application of this method is time-consuming. In some cases, large neutral markers with poor dipolarity/polarizability and hydrogen bonding interactions can be used as hold-up volume markers. This is the case of dodecylbenzene and nonadecane-2-one in clearly HILIC behaving chromatographic systems, the use of decanophenone as a marker can be even extended to the boundary between HILIC and RPLC. The elution volume of the marker remains nearly unaffected by the concentration of ammonium acetate in the mobile phase up to 20 mM. The injection of pure solvents to produce minor base-line disturbance as hold-up markers is strongly discouraged, since solvent peaks are complex to interpret and depend on the ionic strength of the eluent.

Microfluidics technology has grown rapidly over the past decades due to its high surface-to-volume ratios, flow controllability, and length scales efficiently suited for interacting with microscopic elements. However, as a consequence of the small rates of mixing and transfer they achieve due to operating under laminar flow regimes, the utilization of microfluidics for energy applications has long been a key challenge. In this regard, as a result of the hydrodynamic and thermophysical properties they exhibit in the vicinity of the pseudo-boiling region, it has recently been proposed that microconfined turbulence could be achieved by operating at high-pressure transcritical fluid conditions. Nonetheless, the underlying flow mechanisms of such systems are still not well characterized, and, thus, need to be carefully investigated. This work, consequently, analyzes supercritical microconfined turbulence by computing direct numerical simulations of high-pressure ([Formula: see text]) N2 at transcritical conditions imposed by a temperature difference between the bottom ([Formula: see text]) and top ([Formula: see text]) walls for a friction Reynolds number of [Formula: see text] (bottom wall). The results obtained indicate that microconfined turbulence can be achieved under such conditions, leading to mixing and heat transfer increments up to [Formula: see text] and [Formula: see text], respectively, with respect to equivalent low-pressure systems. In addition, it is found that the near-wall flow physics deviates from a single-phase boundary layer theory due to the presence of a baroclinic instability in the vicinity of the hot/top wall. This instability is generated by the combination of the external force driving the flow and the large variation of density across the pseudo-boiling region, which strongly modifies the flow behavior in the vicinity of the wall and renders present “law of the wall” transformation models inaccurate.

The study of complex multiscale flows [@Groen2014-A], like for example the motion of small-scale turbulent eddies over large aerodynamic structures [@Jofre2022-A], microconfined high-pressure supercritical fluids for enhanced energy transfer [@Bernades2022-A], or hydrodynamic focusing of microorganisms in wall-bounded flows [@Palacios2022-A], greatly benefits from the combination of interconnected theoretical, computational and experimental approaches. This manifold methodology provides a robust framework to corroborate the phenomena observed, validate the modeling assumptions utilized, and facilitates the exploration of wider parameter spaces and extraction of more sophisticated insights. These analyses are typically encompassed within the field of Predictive Science & Engineering [@Njam2009-A], which has attracted attention in the Fluid Mechanics community and is expected to exponentially grow as computational studies transition from (mostly) physics simulations to active vectors for scientific discovery and technological innovation with the advent of Exascale computing [@Alowayyed2017-A]. In this regard, the computational flow solver presented aims at bridging the gap between studying complex multiscale flow problems and utilizing present and future state-of-the-art supercomputing systems in academic environments. The solver presented is named RHEA, which stands for open-source Reproducible Hybrid-architecture flow solver Engineered for Academia, and is available as an open-source Git repository at https://gitlab.com/ProjectRHEA/flowsolverrhea.

Cavitation is an important issue in pumped storage unit as it can compromise the safe and stable operation of the unit. The present work aims revealing the dynamic behavior of a pump-turbine runner in cavitating flow from a perspective of fluid-structure interaction. A procedure is developed to map the cavities from computation fluid dynamics simulation to finite element model. The calculated flow rate and head agree well with experimental results. A nonlinear relationship between the sonic speed in cavity and vapor volume fraction is applied in the finite element model. The effect of the sonic speed and fluid density on the dynamic behavior of the runner, and their coupled effect are investigated, respectively. Then the modal characteristics of the runner in cavitating flow are analyzed by solving the first 8000 modes, and a harmonic analysis is carried out to determine the main global mode. The results show that the sonic speed (20 m/s–100 m/s) could have a greater effect than the added mass for some modes. Finally, it is shown that the complexity and number of nodal diameter modes greatly increases in cavitating flow, with a lot of local modes which are similar to global nodal diameter mode. This work provides a method for evaluating the dynamic behavior of the pump-turbine runner in cavitating flow and could contribute to the safe operation of the pump-turbine unit.

Different aspects related to Computational Fluid Dynamics (CDF) will be studied. First, theoretical aspects needed for the resolution of this kind of problems with the finite element method are reviewed. Then, the heat equation is also reviewed. After that, the generic convection diffusion equation is studied, and different convective schemes are used (CDS, UDS, SUDS and QUICK). Numerical experiments are conducted to compare them between each other. Then the problems that arise when trying to numerically solve the Navier Stokes equations are reviewed. These include the checkerboard problem and the fact the the equations are highly coupled. The equations will be solved for different cases, amongst them the Lid-Driven Cavity, using the convective schemes studied previously with a collocated mesh and a fractional step method. Finally, the energy equation is coupled with the Navier-Stokes equations, where the body forces that were previously neglected are also added. This allows the simulation of natural convection cases. The cases studied is that of a cavity with walls at different temperatures, which causes the fluid motion. This case is solved with a Staggered Mesh

Aerodynamic performances may be optimised by the appropriate tuning of Active Flow Control (AFC) parameters. For the first time, we couple Genetic Algorithms (GA) with an unsteady Reynolds-Averaged Navier-Stokes (RANS) solver using the Spalart-Allmaras (SA) turbulence model to maximise lift and aerodynamic efficiency of an airfoil in stall conditions [1], and then validate the resulting set of optimal Synthetic Jet Actuator (SJA) parameters against well-resolved three-dimensional Large Eddy Simulation (LES). The airfoil considered is the SD7003, at the Reynolds number and the post-stall angle of attack . We find that, although SA-RANS is not quite as accurate as LES, it can still predict macroscopic aggregates such as lift and drag coefficients, provided the free-stream turbulence is prescribed to reasonable values. The sensitivity to free-stream turbulence is found to be particularly critical for SJA cases. Baseline LES simulation agrees well with literature results, while RANS-SA would seem to remain a valid model to a certain degree. For optimally actuated cases, our LES simulation predicts far better performances than obtained by suboptimal SJA LES computations as reported by other authors [2] for the same airfoil, Re and a, which illustrates the applicability and effectiveness of the SJA optimisation technique applied, despite using the less accurate yet computationally faster SA-RANS. The flow topology and wake dynamics of baseline and SJA cases are thoroughly compared to elucidate the mechanism whereby aerodynamic performances are enhanced This work was supported by the Spanish Government under grants FIS2016-77849-R and PID2020-114043GB-I00 and by the Catalan Government under grant 2017-SGR-00785. Computations were performed in the Red Española de Supercomputación (RES), Spanish supercomputer network, under the grants IM-2019-3-0002 and IM-2020-1-0001. F. M. is a Serra-Húnter fellow

International audience; The clustering, collision, and relaxation dynamics of pristine and doped helium nanodroplets is theoretically investigated in cases of pickup and clustering of heliophilic argon, collision of heliophobic cesium atoms, and coalescence of two droplets brought into contact by their mutual long-range van der Waals interaction. Three approaches are used and compared with each other. The He time-dependent density functional theory method considers the droplet as a continuous medium and accounts for its superfluid character. The ring-polymer molecular dynamics method uses a path-integral description of nuclear motion and incorporates zero-point delocalization while bosonic exchange effects are ignored. Finally, the zero-point averaged dynamics approach is a mixed quantum–classical method in which quantum delocalization is described by attaching a frozen wavefunction to each He atom, equivalent to classical dynamics with effective interaction potentials. All three methods predict that the growth of argon clusters is significantly hindered by the helium host droplet due to the impeding shell structure around the dopants and kinematic effects freezing the growing cluster in metastable configurations. The effects of superfluidity are qualitatively manifested by different collision dynamics of the heliophilic atom at high velocities, as well as quadrupole oscillations that are not seen with particle-based methods, for droplets experiencing a collision with cesium atoms or merging with each other.

The world is going through a constant evolution, where the objectives are much more ambitious than before thanks to the new technologies. However, the focus is no longer on only improving existing services without considering anything else; nowadays, the benefit provided is just as important as the way in which it is achieved, and the main efforts currently are focused on achieving a sustainable world, in which life continues to be as we know it and climatic catastrophes are eradicated, at least those in which human activity is the main cause. That is why this thesis is focused on the implementation in the aeronautical industry of a promising technology called Active Flow Control (AFC). To that end, an exhaustive state-of-the-art is conducted in which the AFC technology is described in general, to then deep dive in its aeronautical applications. Next, the technology required so as to implement the AFC in an aircraft is described, covering the main elements needed to influence the flow around the aircraft together with the power supply architectures necessary to feed the actuators. On the other hand, and based on the information previously gathered, a Minimum Viable Product (MVP) is defined, in which AFC technology is to be implemented in an Airbus A-320 aircraft. In the MVP, both the technological elements that need to be installed together with the system infrastructure are established, thus defining the architecture of the product. In order to ensure the viability and profitability of the MVP, a feasibility study is conducted, analysing the installation of the product from an airline perspective considering three different casuistic: an aircraft that flies only at national level in Spain, an aircraft that flies at international level in Europe and a complete fleet of Airbus A-320 that flies at international level in Europe. The preliminary economic analysis covers the three cases mentioned, and the complete economic figures are presented for the third case, the one with more practical interest. On the other hand, the regulatory emissions framework currently in place in Europe is described, assessing whether the installation of the MVP in a European airline could influence the overall company strategy towards the 2050 zero net goal achievement. Due to the current situation, in which the global awareness of contaminant gases emissions has increased considerably, all the projects aiming to reduce this type of emissions have a great impact in the industry, and the AFC technology investigations are a good opportunity to improve aeronautical industry contaminant footprint in the world.

Spontaneous capillary imbibition is a classical problem in interfacial fluid dynamics with a broad range of applications, from microfluidics to agriculture. Here we study the duration of the cross-over between an initial linear growth of the imbibition front to the diffusive-like growth limit of Washburn's law. We show that local-resistance sources, such as the inertial resistance and the friction caused by the advancing meniscus, always limit the motion of an imbibing front. Both effects give rise to a cross-over of the growth exponent between the linear and the diffusive-like regimes. We show how this cross-over is much longer than previously thought – even longer than the time it takes the liquid to fill the porous medium. Such slowly slowing-down dynamics is likely to cause similar long cross-over phenomena in processes governed by wetting.

In this study Computational Fluid Dynamics (CFD) are used to predict the air flow structure and pollutant retention inside urban canyons taking into account thermal effects due to solar radiation in order to imitate diurnal heating over a city. The diurnal heating induces buoyancy therefore the flow structure and pollutant concentration will be completely different depending on the daytime. The presented method departs from a 2D domain comprised by eight urban canyons of aspect ratio 1 and different 2D transient RANS (Reynolds-Averaged Navier-Stokes) simulations that have been conducted using OpenFoam. Isothermal, single-surface heating and multi-surface heating cases are considered. For all of them, the results obtained have been post-processed using ParaView and Matlab to be able to analyse all the information related with velocity, pressure, temperature, pollutant concentration, streamlines, etc. These results have been also contrasted and validated with data obtained from wind-tunnel experiments and other CFD simulations which have been conducted using a 2D model and conditions similar to the ones used in this thesis. Finally, the conclusions obtained for an airflow with a Reynolds number of 12000 are that for most cases, a single main vortex is formed which is strengthen for the cases where leeward or ground surfaces are heated up compared to the vortex formed in isothermal case. In all cases where the windward side is heated up, a second counter-rotating vortex appears due to buoyancy and displaces the main one from the center of the canyon. Also, when the windward side is heated, the concentration of pollutants increases at the pedestrian level which may be considered as the worst case. Further improvements may be considered to continue with this work such as improving the mesh quality, considering an additional heat source, using another turbulence modelling (LES) or even considering a 3D model since the buoyant flows have an unsteady and 3D characteristc that require complex numerical models to obtain more accurate results

[eng] This thesis contains my doctoral research in condensed soft matter physics prepared at the University of Barcelona. It covers the interaction of active Janus particles with liquid-liquid and liquid-solid interfaces, both experimentally and computationally. The structure of this thesis is made up of three parts. In the first part I address the need to obtain methods and devices for experimental analysis. This discussion is divided into 3 chapters. In the first I show how to create active Janus particles and new microfluidic devices necessary for the development of the thesis. Various techniques are detailed, such as drop casting, sputtering, plasma cleaner, PDMS printing by 3D printer, lithography or spin coating. In the second chapter I show how to correctly record, store and compress the experimental videos, in order to obtain values such as the velocity, the rotational Brownian time or the translational diffusion constant of these particles. These measurements also depend on the duration of the recorded videos, and on how many frames per second are used. Thus, in this chapter I also analyse what effect these parameters have for the above calculation, and what parameters are optimal to achieve lighter videos. I also offer a software solution to compress captured videos further, if possible. Finally, in the third chapter I show how to capture the movement of the particles, using both traditional and novel techniques based on neural networks. The chapter shows how to manipulate particle trajectories using image processing algorithms and ends with a neural network-based particle tracking program capable of detecting hundreds of these colliding particles without losing their identity. In the second part of this thesis I study the interaction of these particles at the individual level with liquid- liquid interfaces. This part begins with an experimental chapter, where the study of the behaviour of particles that move on a solid surface and contact these liquid interfaces. To do this, I analyse the time they are in the interface after contacting it, the distance they travel along them and the orientation they have in them. The particles acquire a defined orientation that allows them to travel longer distances and for a longer time than expected, so these interfaces are useful to guide particles. These experiments are complemented with a small theoretical model, but it is insufficient to explain the results and therefore in the next chapter I develop an advanced model based on a hybrid Lattice-Boltzmann-Finite Element algorithm, where I exploit a model of active self- diffusiophoretic particles that interact with a dissolved medium asymmetrically between both sides of the interface. This model is capable of reproducing the behaviour of the particles in the interface and allows to study in detail the innate effect of the capillarity present in inactive particles and the extra component added in the active ones due to its attraction and phoretic production. The third and last part of this thesis, composed of a single chapter, explores how we can take advantage of the interaction of active particles with interfaces to obtain an accumulation system. This system is based on the use of solid-liquid interfaces with a complex geometry where the unit cells of the system do not break the detailed balance. The change in the type of interfaces was because active particles behaved in a similar way in the presence of liquid-liquid and solid-liquid interfaces, but they are simple to create a complex geometry. The chapter includes a model based on the theory of topological insulators that can predict the experimental behaviour, and with it we experimentally demonstrate behaviours predicted in the theory of topological insulators., [spa] Esta tesis contiene mi investigación doctoral en física de la materia blanda condensada elaborada en la Universidad de Barcelona. Cubre la interacción de las partículas Janus activas con interfases líquido-líquido y líquido-sólido, tanto experimentalmente como computacionalmente. La estructura de esta tesis se compone de tres partes. En la primera parte abordo la necesidad de obtener métodos y dispositivos para el análisis experimental. Esta discusión se divide en 3 capítulos. En el primero muestro cómo crear partículas Janus activas y nuevos dispositivos microfluídicos necesarios para el desarrollo de la tesis. En el segundo muestro cómo grabar, almacenar y comprimir correctamente los vídeos experimentales, optimizando los parámetros característicos del sistema. En el tercero muestro cómo capturar el movimiento de las partículas, usando tanto técnicas tradicionales como novedosas basadas en redes neuronales. En la segunda parte de esta tesis estudio la interacción de estas partículas a nivel individual con interfases líquido-líquido. En el primer capítulo de esta parte explico mis estudios desde un punto de vista experimental. La necesidad de una mejor explicación de los experimentos me hizo considerar desarrollar un modelo avanzado basado en un algoritmo Lattice-Boltzmann, que muestro en el siguiente capítulo. En cualquier caso, en ambos capítulos vemos cómo se pueden guiar las partículas activas utilizando interfases líquido-líquido. La tercera y última parte de esta tesis, compuesta de un único capítulo, explora cómo podemos aprovechar la interacción de partículas activas con interfases para obtener un sistema de acumulación. Este sistema se basa en el uso de interfases sólido-líquido con una geometría compleja donde las celdas unitarias del sistema no rompen el equilibrio detallado. El cambio del tipo de interfases fue debido a que las partículas activas se comportaron de manera similar en presencia de interfases líquido-líquido y sólido-líquido, pero éstas últimas son sencillas de crear para una geometría compleja.

L'objectiu d'aquest treball de final de màster és la implementació i validació, mitjançant exemples en la literatura, de la llei constitutiva de Herschel-Bulkley de la dinàmica de fluids mitjançant el mètode d'elements finits de partícules (PFEM). La base del treball és la formulació PFEM per a fluids Bingham implementada a la plataforma del codi obert Kratos Multiphysics. El model de Herschel-Bulkley relaciona el tensor de tensions tallant amb el tensor de velocitat de deformació tenint en compte el límit elàstic, que limita l'inici o el final del moviment del fluid; la viscositat del fluid, que és responsable de la resistència del fluid al moviment; i l'índex del fluid, un paràmetre que representa el nivell de no-linealitat del moviment. La llei de Herschel-Bulkley és validada amb problemes de referència de la literatura. Es duu a terme la convergència en l'espai i el temps, l'anàlisi de sensibilitat de les variables del model i les comparacions amb el model estàndard de Bingham. A més, s'aplica l'anomenada regularització de Papanastasiou per a evitar els inconvenients numèrics del model de Herschel-Bulkley. Tots els resultats son graficats al llarg del treball i es comparen amb referències numèriques i experimentals trobades en articles científics. Al llarg dels càlculs numèrics és possible calibrar una sèrie de paràmetres fonamentals per a les simulacions amb el model. El objetivo de este trabajo de final de máster es la implementación y validación, mediante ejemplos en la literatura, de la ley constitutiva de Herschel-Bulkley de la dinámica de fluidos mediante el método de elementos finitos de partículas (PFEM). La base del trabajo es la formulación PFEM para fluidos Bingham implementada en la plataforma de código abierto Kratos Multiphysics. El modelo de Herschel-Bulkley relaciona el tensor de tensiones cortante con el tensor de velocidad de deformación teniendo en cuenta el límite elástico, que limita el inicio o el final del movimiento del fluido; la viscosidad del fluido, que es responsable de la resistencia del fluido al movimiento; y el índice del fluido, un parámetro que representa el nivel de no linealidad del movimiento. La ley de Herschel-Bulkley se valida con problemas de referencia de la literatura. Se lleva a cabo la convergencia en el espacio y el tiempo, el análisis de sensibilidad de las variables del modelo y las comparaciones con el modelo estándar de Bingham. Además, se aplica la llamada regularización de Papanastasiou para evitar los inconvenientes numéricos del modelo de Herschel-Bulkley. Todos los resultados se grafican a lo largo del trabajo y se comparan con referencias numéricas y experimentales encontradas en artículos científicos. A lo largo de los cálculos numéricos es posible calibrar una serie de parámetros fundamentales para las simulaciones con el modelo. The objective of this master's thesis is the implementation and validation, by means of literature examples, of the Herschel-Bulkley constitutive law in fluid dynamics in a particle finite element method (PFEM). The basis of the work is the PFEM formulation for Bingham fluids implemented in the open-source platform Kratos Multiphysics. The Herschel-Bulkley model relates the shear stress tensor to the strain rate tensor taking into account the yield stress, which limits the beginning or the end of the fluid motion; the fluid viscosity, which is responsible for the fluid's resistance to motion; and the fluid index, a parameter representing the level of nonlinearity of the motion. The Herschel-Bulkley law is validated with benchmark problems from the literature. Convergence in space and time, sensitivity analysis of the model variables and comparisons with the standard Bingham model are carried out. In addition, the so-called Papanastasiou regularization is applied to avoid numerical drawbacks arisign from the Herschel-Bulkley model. All results are plotted throughout the paper and compared to both numerical and experimental references found in scientific articles. Throughout the numerical calculations it is possible to calibrate a series of fundamental parameters for simulations with the model.

We optimise a set of Synthetic Jet (SJ) Active Flow Control (AFC) parameters on a SD7003 airfoil in order to maximise lift and aerodynamic efficiency. 2D-RANS with the Spallart Almaras (SA) turbulence model is employed in the optimisation process. The optimal set of SJ parameters is then tested using LES. Comparison between 2D RANS-SA and 3D LES results shows the necessity of tuning the SA model parameters to further improve the reliability of a 2D-simulation-based optimisation. Notwithstanding this, both RANS-SA and LES results show that airfoil efficiency can be drastically improved with SJ AFC

The availability of high fidelity data due to the recent developments in high-performance computing(HPC), has opened new doors for wall modeling in Large Eddy Simulation(LES). By augmenting the physics-based model with information gained from data, new methodologies of model development are being developed. Towards this goal, a preliminary work on developing a non-equilibrium wall model is presented here briefly describing the method.

A common approach in aerodynamic design is to optimize a performance function—provided some constraints—defined by a choice of an aerodynamic model at nominal operating conditions. Practical experience indicates that such a deterministic approach may result in considerably sub-optimal designs when the adopted aerodynamic model does not lead to accurate predictions, or when the actual operating conditions differ from those considered in the design. One approach to address this shortcoming is to consider an average or robust design, wherein the statistical moments of the performance function, given the uncertainty in the operating conditions and the aerodynamic model, is optimized. However, when the number of uncertain inputs is large or the performance function exhibits significant variability, an accurate evaluation of these moments may require a large number of function evaluations at each optimization iteration, rendering the problem significantly expensive. To tackle this difficulty, we consider a variant of the stochastic gradient descent method where in each iteration, a stochastic approximation of the objective, constraints, and their gradients is generated. This is done via a small number of forward/adjoint solutions corresponding to random selections of the uncertainties. The methodology is applied to the robust optimization of the NACA-0012 airfoil subject to operating condition and turbulence model uncertainty. With a cost that is only a small factor larger than that of the deterministic methodology, the stochastic gradient approach significantly improves the performance of the aerodynamic design for a wide range of operating conditions and turbulence models.

We study the flow past a square cylinder immersed in the wake of an upstream splitter plate separating two different-velocity streams. The bottom stream Reynolds number, ReB = 56 is kept constant for all cases, while the top-to-bottom Reynolds numbers ratio R = ReT/ReB is in the range R ¿ [1,6.5], corresponding to a variation of the bulk Reynolds number Re = (ReT +ReB)/2 ¿ [56, 210]. The onset of vortex-shedding, at R = 2.1 ± 0.1 (corresponding to Re = 86.8 ± 2.8), is pushed to higher Re as compared to the square cylinder in the classic configuration. The threedimensionality is triggered by a mode-C-type instability at R ¿ 3.1 (Re ¿ 115) with wavelength ¿z ¿2.5±0.1, similar to the mode reported for square cylinders placed at an incidence. For a velocity ratio R = 3.4 the flow is period-doubled and exhibits three spanwise symmetries: a mirror reflection and two spatiotemporal symmetries. The road to spatio-temporal chaos is initiated thereafter with a modulational period-doubling tertiary bifurcation at R ¿ (3.4,3.8) that also doubles the spanwise periodicity. The resulting nonlinear solution repeats after four vortex shedding cycles and retains only a spatiotemporal invariance consisting in the evolution by half a period followed by mirror reflection about a streamwise-cross-stream plane. At slighlty higher values R = 4, the flow becomes spatio-temporally chaotic, but the main features of mode C are still observable

Volume of fluid (VOF) method with its Piecewise Linear Interface Calculation (PLIC) reconstruction algorithm is one of the most popular approaches in numerical simulation of interfacial flows with a wide range of applications in different areas. In an effort to evaluate the similarity of the PLIC-generated planes in comparison with the exact interface, a point-cloud, based on the polygon centers of PLIC planes is extracted, which later is used to form a triangular grid that represents the estimated interface. The main objective of this article is to evaluate the interface geometrical properties based on the extracted triangular grid of the interface. The methods presented in this article, characterized by a higher spatially convergence ratio, are compared with the commonly used methods. The proposed methods are tested for two 3-dimensional general test cases, where an evident improvement is seen in calculation accuracy and spatial convergence of the errors of interface normal vector and curvature. This work has been financially supported by MCIN/AEI/10.13039/ 501100011033 Spain, project PID2020-115837RBI00. E. Schillaci acknowledges the financial support of the Programa Torres Quevedo (PTQ2018-010060).

La dinàmica d'un fluid ideal en un espai 2-dimensional pot ser aproximat mitjançant la evolució de N vortexs singulars a mesura que fem tendir N cap a infinit. Al llarg d'aquest treball estudiem la dinàmica de vortexs singulars, normalment denominats com "point vortices", en una superficie no orientable com és l'espai projectiu real, $\RP^2$. Primer estudiem les equacions de Euler per fluids incompressibles així com la seva generalització a varietats no orientables. L'objectiu es obtenir un nou model de vortexs singulars que sigui compatible amb varietats no orientables. Veurem que la dinamica de N vòretxs en un espai projectiu pot ser visualitzat com la dinàmica de N dipols antipodals en l'esfera $S^2$, la qual és un espai recobridor de dos fulls de l'espai projectiu. En la segona part del treball presentem un estudi dels casos integrables, en el sentit de Liouville, a $\RP^2$ entre els quals trobem tant fenòmens nous com fenòmens similars als que es tenen en el problema estandar a l'esfera. Dins de l'estudi incluim l'estudi de fenòmens de equilibri estàtic, equilibri dinàmic, estabilitat i del fenòmen de col·lapse singular. La dinámica de un fluido ideal en un espacio de dimensión 2 puede ser aproximado mediante la evolución de N vortices singulares a medida que N tiende a infinito. A lo largo de este trabajo estudiamos la dinámica de vortices singulares (point vortices) en una superficie no orientable, el plano proyectivo. Primero estudiamos las equaciones de Euler para fluidos incompressibles asi como su generalización para variedades no orientables. La intencion es obtener un nuevo modelo de vortices singulares que sea compatible con la no-orientabilidad de la variedad. Veremos que la dinámica de N vortices en el espacio proyectivo es equivalente a la dinámica de N dipolos antipodales en la esfera, la cual es un recubrimiento de 2 hojas del espacio proyectivo. En la siguiente parte presentamos una comparación de los casos integrables, en el sentido de Liouville, en RP^2 con dinámicas analogas en S^2. Veremos que la dinámica de N vortices en el espacio proyectivo presenta algunas similitudes con el problema estándar así como algunas diferencias. Dentro del trabajo incluimos el estudio de equilibrios estáticos, relativos, estabilidad y colapso singular. The motion of an ideal two-dimensional fluid can be approximated by the evolution of N point vortices, as N → ∞. Throughout this work, we study the motion of point vortices on a non- orientable surface, the projective plane RP2. First, we study the incompressible Euler equations, as well as their generalization to non-orientable manifolds. The aim is to derive a new model for point vortices that is compatible with non-orientability. We will see that the motion of N vortices on the projective space can be regarded as the motion of N antipodal dipoles on the sphere S2, the orientation cover of RP2. In the next part, we will present a comparison of the integrable cases of the vortex motions on RP2 with analogous motions on S2 describing new phenomena, as well as similarities. Among the cases we study, we include the study of equilibria, relative equilibria, their stability, and collapse. Outgoing

The transition between the stable base state of the magnetized spherical Couette (MSC) flow and the return flow instability is experimentally investigated. The experiments are conducted using an MSC setup consisting of insulating spheres with the ratio of the inner to the outer radii r i/r o = 0.5, Reynolds number Re = 1000 and Hartmann number Ha ∈ [25, 29]. The transition is characterized by changes in the power spectra of the azimuthal modes in the flow as Ha is dynamically changed. The transition occurs in the interval Ha ∈ [26.5, 27.5]. The evolution of the power spectra of the azimuthal modes exhibits hysteretic effect depending on whether Ha is increased or decreased within the experimental interval. The power spectra in the azimuthal modes m ∈ {3, 4} increases and remains dominant as Ha is increased, while the power spectra in m ∈ {2, 4} are dominant while the flow is time dependent due to return flow instability as Ha is decreased.

The final publication is available at Springer via http://dx.doi.org/10.1007/s11242-021-01721-z. Mixing is pivotal to conservative and reactive transport behaviors in porous media. Methods for investigating mixing processes include mathematical models, laboratory experiments and numerical simulations. The latter have been historically limited by the extreme computational resources needed for solving flow and transport at the microscopic scale within the complex pore structure of a three-dimensional porous medium, while dealing with a sufficiently large domain in order to generate meaningful emergent continuum-scale observables. We present the results of such a set of virtual column experiments, which have been conducted by taking advantage of modern high-performance computing infrastructure and Computational Fluid Dynamics software capable of massively parallel simulations. The computational approach has important advantages such as full control over the experimental conditions as well as high spatial and temporal resolution of measurements. Hydrodynamic dispersion results agree with the empirical and theoretical literature and link dispersivity to median grain size, while elucidating the impact of grain size variability on the critical Péclet number. Reactive transport results also indicate that the relative degree of incomplete mixing is related to the granular material’s mean hydraulic radius and not directly to the median grain size. When compared to a well-known laboratory experiment with similar configuration, less incomplete mixing is observed in our simulations. We offer a partial explanation for this discrepancy, by showing how an apparent nonlinear absorbance–concentration relationship may induce laboratory measurement error in the presence of local concentration fluctuations. The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by the Barcelona Supercomputing Center (research activity AECT-2019-3-0014). D. B. acknowledges financial support by the U.S. Army Research Office under Contract/Grant W911NF-18-1-0338. D. F. acknowledges financial support by the European Commission through project MARSOLUT (H2020-MSCA-ITN-2018), and by the Spanish Ministry of Science, Innovation and Universities through project MONOPOLIOS (RTI2018-101990-B-I00). The authors thankfully acknowledge Charles F. Harvey for sharing the G02 light absorbance data. This work was partially funded by the U.S. Army Research Office (W911NF-18-1-0338), the European Commission (H2020-MSCA-ITN-2018), and the Spanish Ministry of Science, Innovation and Universities (RTI2018-101990-B-I00).

The present work studies the hydro-gasdynamic analogy between a shock wave, occurring in supersonic internal or external compressible flows, and a hydraulic jump, a sort of normal shock occurring in open-channel flows. It consists of an extensive theoretical framework followed by a practical analysis, the aim of which was to experimentally trigger the hydraulic jump, both normal and oblique, while using a low-cost designed lab prototype. The assembly development, called ‘water table’, arises from the necessity of economical alternatives to expensive supersonic wind tunnels in the experimental study of compressible fluid dynamics. With this objective in mind, a hydraulic canal based on a Laval nozzle was constructed where water flow could accelerate from subcritical to critical to supercritical regime and then return to subcritical regime through a hydraulic jump. In addition, multiple design alternatives were evaluated considering environmental, economic, functional and aesthetics factors. A low-cost implementation was the critical criterion in the design process. The measurements have revealed that the geometry of the nozzle and the wedges designed as obstacles to cause obliquity are the most significant and influential elements in the formation of a hydraulic jump in the experimental set-up. Regarding the experimental variables, the experiments demonstrate the effect of the upstream and downstream heights of the hydraulic jump in the data collection. This experience is a step forward in supporting students in the understanding of compressible flow and its principles by providing an in-house experimental set-up that promotes active learning, motivation and interest in fluid mechanics.

The aim of this study is to determine through numerical simulations the extent and robustness of the three-dimensional torsional dynamics of the thermal convection in rotating spherical fluids at very low Prandtl numbers. It is known that the kinetic energy of the periodic axisymmetric flows propagates latitudinally on the surface of the sphere. Here, it is shown that when the axisymmetry is broken at a secondary Hopf bifurcation, the flow starts to drift in the azimuthal direction giving rise to a quasiperiodic motion that propagates the energy in latitude and longitude. The double direction of propagation gives rise to a meandering path of the kinetic energy, which is still concentrated on the surface, but highly localized. Several new stable states of convection with different symmetries have been identified in a large range of Rayleigh numbers, all of them retaining the torsional motion of the basic velocity field. Particular attention is paid to their dependence on the Rayleigh number and on the values of the frequencies, of the mean zonal flow, and of the kinetic energy of the fluid.

Active nematic fluids confined in narrow channels are known to generate spontaneous flows when the activity is sufficiently intense. Recently, it was demonstrated [R. Green, J. Toner, and V. Vitelli, Phys. Rev. Fluids 2, 104201 (2017)] that if the molecular anchoring at the channel walls is conflicting, i.e., perpendicular on one plate and parallel on the other, flows are initiated even in the zero activity limit. An analytical laminar velocity profile for this specific configuration was derived within a simplified nematohydrodynamic model in which the nematic order parameter is a fixed-magnitude unit vector n. The solution holds in a regime where the flow does not perturb the nematic order imposed by the walls. In this study, we explore systematically active flows in this confined geometry with a more general theoretical model that uses a second-rank tensor order parameter Q to express both the magnitude and orientation of the nematic phase. The Q-model allows for the presence of defects and biaxial, in addition to uniaxial, molecular arrangements. Our aim is to provide a unified picture, beyond the limiting regime explored previously, to serve as a guide for potential microfluidic applications that exploit the coupling between the orientational order of the molecules and the velocity field to finely control the flow and overcome the intrinsic difficulties of directing and pumping fluids at the microscale. We reveal how the nematic-flow coupling is not only dependent on geometrical constraints, but is also highly sensitive to material and flow parameters. We specifically stress the key role played by the activity and the flow aligning parameter, and we show that solutions mostly depend on two dimensionless parameters. We find that for large values of the activity parameter, the flow is suppressed for contractile particles while it is either sustained or suppressed for extensile particles depending on whether they tend to align or tumble when subject to shear. We explain these distinct behaviors by an argument based on the results of the stability analysis applied to two simpler configurations: active flows confined between parallel plates with either orthogonal or perpendicular alignment at both walls. We show that the analytical laminar solution derived for the n model in the low activity limit is found also in the Q model, both analytically and numerically. This result is valid for both contractile and extensile particles and for a flow-tumbling as well as aligning nematics. We remark that this velocity profile can be derived for generic boundary conditions. To stress the more general nature of the Q model, we conclude by providing a numerical example of a biaxial three-dimensional thresholdless active flow for which we show that biaxiality is especially relevant for a weakly first-order isotropic-nematic phase transition.

Study region Two giant pockmarks in Lake Banyoles (NE Spain) have been surveyed over the last 35 years. The giant pockmark ‘B1’ has maintained an ‘eruptive’ mode with permanent groundwater discharge, whereas, the giant pockmark ‘B2’ has displayed alternating quiescent and eruptive phases. Study focus Interannual variability of lake-subsurface groundwater discharge in both pockmarks and the main lake aquifer level correlates with changes in the accumulated rainfall during the previous 10 months in the north-east of Spain. In the eruptive phase, the lutocline, marking the top of suspended sediments, is warmer than the ambient lake water and generates a turbid hydrothermal plume. New hydrological insights for the Region: Results show that the permanent hydrothermal plume at pockmark B1 is no longer penetrating the lake's background stratification due to the loss of plume buoyancy. The available data demonstrate that current climate change coupled with a depletion of groundwater resources has strongly impacted the hydrogeology and limnology of the main pockmark of the lake and also the distribution of suspended sediment in the water column Open Access funding provided thanks to the CRUE-CSIC agreement with Elsevier

Pycnometric and homologous series retention methods are used to determine the volume and mean composition of the water-rich layers partially adsorbed on the surface of several hydrophilic interaction liquid chromatography (HILIC) column fillings with acetonitrile-water and methanol-water as eluents. The findings obtained in this work confirm earlier studies using direct methods for measuring the stationary phase water content performed by Jandera's and Irgum's research groups. Water is preferentially adsorbed on the surface of the HILIC bonded phase in hydroorganic eluents containing more than 40% acetonitrile or 70% methanol, and a gradient of several water-rich transition layers between the polar bonded phase and the poorly polar bulk mobile phase is formed. These layers of reduced mobility act as HILIC stationary phases, retaining polar solutes. The volume of these layers and concentration of adsorbed water is much larger for acetonitrile-water than for methanol-water mobile phases. In hydroorganic eluents with less than 20-30% acetonitrile or 40% methanol the amount of preferentially adsorbed water is very small, and the observed retention behavior is close to the one in reversed-phase liquid chromatography (RPLC). In eluents with intermediate acetonitrile-water or methanol-water compositions a mixed HILIC-RPLC behavior is presented. Comparison of several HILIC columns shows that the highest water enrichment in the HILIC retention region for acetonitrile-water mobile phases is observed for zwitterionic and aminopropyl bonded phases, followed in minor grade for diol and polyvinyl alcohol functionalizations. Pentafluorophenyl bonded phase, usually considered a HILIC column, does not show significant water adsorption, nor HILIC retention.

Conventional municipal waste management systems based on collecting and storing waste for future management are cost-effective and flexible. These systems present significant problems such as odours, plagues and hygiene problems caused by their storage and greenhouse gas emissions from garbage trucks used for the transport of waste. The Automated Waste Collection System (AWCS) and Automated Vacuum Waste Collection (AVWC) systems, in which waste is transported directly underground to the processing plants, are efficient collection systems and respectful of the environment as alternatives to traditional systems. The pneumatic system reduces the value of the per capita generation of general waste. The present study explains the origin of pipe failure in two different AWCS factories, as well as the identification of the failure phenomena. To carry out the study, a classification of 90 failure cases by primary cause was performed, followed by recommendations to avoid these failures in the future. Moreover, a computational fluid dynamics (CFD) simulation was performed in order to help in the failure determination and the key recommendations to avoid the most common and frequent failures.

The incompressible Navier-Stokes equations stand as the best mathematical model for turbulent flows. However, direct numerical simulations at high Reynolds numbers are not yet feasible because the convective term produces far too many relevant scales of motion, thus remaining limited to relatively low-Reynolds numbers. Dynamically less complex mathematical formulations have been developed for coarse-grain simulations, like the well known eddy-viscosity models. Most of these models are based on the combination of invariants of a symmetric tensor that depends on the gradient of the resolved velocity field, G = Ñu, and should properly detect different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime, etc.). Brand-new models have been constructed considering the first three invariants of the symmetric tensor GGT with excellent results;1 hence, it is formally based on the lowest-order approximation of the subgrid stress tensor, t(u) = D2 12GGT +O(D4), i.e. the gradient model proposed by Clark.2 Furthermore, these models have been implemented on a pseudo-spectral algorithm with a fully-explicit second-order time-integration method.3 The performance of this special configuration has been successfully tested for decaying isotropic turbulence and a turbulent channel flow. It is currently being developed for a semi-infinite boundary layer with periodic conditions as a previous step to carry out wind farm simulations. Details of the implementation and numerical results will be presented. The work has been financially supported by a competitive R+D project (ENE2017-88697-R) by the Spanish Research Agency. The authors thankfully acknowledge these institutions.

This report aspires to deepen in the field of Computational Fluid Dynamics (CFD) and detail the steps to convert a physical phenomenon into a solvable domain. Four parts can be clearly differenced along this thesis. First, we set basic concepts such as governing equations, numerical methods and schemes, solvers and algorithms which are essential for the resolution of any real case. Secondly, we give a brief overview of turbulence and its modelling. Then we resolve three well-known didactic exercises of forced, natural and mixed convection and compare our results to benchmark solutions. Finally, we make an introduction to Thermal Comfort and apply all previous knowledge for the study of thermal comfort inside a room. For the resolution of the exercises, we used a self-developed C++ code due to its good efficiency in resolving computationally expensive algorithms. The results obtained in the first three didactic exercises are in accordance with the benchmark solutions, and hence we conclude our code is well-implemented. The layout used in our thermal comfort case gives as a result an acceptable comfort distribution throughout the room. We recommend to take a look at future lines which provide ideas for further thesis

This report presents the procedures and results obtained in the project ’Numerical Simulation of Turbulent Flows Using High Performance Computing’, in which a high performance code for fluid dynamics simulation (SA3) has been extended. Firstly, sub-mesh modelling has been incorporated into the integration of the Navier-Stokes equations using a source term representative of the turbulent transport. This operator has been generalized for any field, its discretization has been implemented and it has been validated by means of the Method of Manufactured Solutions (MMS). The problem is closed by a sub-mesh viscosity calculated by Smagorinsky, WALE and Vreman models. In addition, their boundary conditions have been carefully analysed. These models have also been successfully validated using the MMS method. Finally, the effect of the sub-mesh viscosity on the Courant-FriederichLewis condition has been added for the estimation of the maximum time step, completing the extension of SA3 for the execution of Large-Eddie Simulations (LES). In the second place, the solutions obtained for the case of a Channel Flow are studied, analyzing the capacity of the code to resolve turbulent flows and boundary layers. Therefore, the statistical description of the turbulent flow and the algorithms to calculate its different parameters are presented. Next, a scalability analysis is carried out according to the density of the mesh used, and the profiles of the statistical parameters obtained without using a turbulence model are compared with the profiles obtained using the Vreman and WALE models. Based on the results obtained throughout the project, the conclusions obtained and future recommendations are finally presented

Ferrofluid moving thin films and their possible significance with regard to active flow control for lift and attack angle enhancement are discussed. In this strategy, a very thin film of ferrofluid is strongly attached at the wall of the wing by a normal magnetic field from below and pumped tangentially along the wing. Utilizing a simplified physical model and from the available experimental data on moving walls, the expected lift enhancement and effect on the attack angle were assessed. Additional research and design is required in order to explore the possibilities in the use of ferrofluid moving thin films This research was supported by the Spanish Ministry of Economy and Competitiveness under fellowship grant Ramon y Cajal: RYC-2013-13459

The portability of codes has become a major advantage given the continuous development of new architectures for numerical applications, as well as the progressive incorporation of accelerators in modern supercomputers. Following this trend, we have adopted an algebraic approach in the implementation of a Poisson solver for incompressible flows with one periodic direction. This approach, which basically consists of adapting a reduced set of fundamental operations to any architecture (such as the sparse matrixvector product or the dot product of two vectors), allows us to efficiently port our applications to any heterogeneous supercomputers in an easy manner. More particularly, our three-dimensional solver takes advantage of the existing periodic dimension (by means of a Fourier decomposition) to later execute overlapped data transpositions among devices, which conveniently share the workload with their CPU hosts, and solve the resulting two-dimensional decoupled subsystems. The work has been financially supported by a competitive R+D project (ENE2017- 88697-R) by the Spanish Research Agency. A.A.B is supported by a predoctoral contract (DIN2018-010061) by the Ministry of Science, Innovation and Universities of Spain (MICINN) and X.A.F. by the by the Government of Catalonia (2019FI_B2-00076).

There is a huge number of natural and industrial flows, which are subjected to time-dependent boundary conditions. The flow of a magnetic fluid under the influence of temporal modulations is such an example. Here, we perform numerical simulations of ferrofluidic Couette flow subject to time-periodic modulation (with frequency $$\Omega _H$$ Ω H ) in a spatially homogeneous magnetic field and report how such a modulation can lead to a significant Reynolds number Re enhancement. Consider a modified Niklas approximation we explain the relation between modulation amplitude, driving frequency and stabilization effect. From this, we describe the system response around the primary instability to be sensitive/critical by an alternating field. We detected that such an alternating field provides an easy and in particular accurate controllable key parameter to trigger the system to change from subcritical to supercritical and vice versa. Our findings provide a framework to study other types of magnetic flows driven by time-dependent forcing.

An advanced numerical model is presented for the simulation of wave-induced free-surface flow, utilizing an efficient hybrid parallel implementation. The model is based on the solution of the Navier–Stokes equations using large-eddy simulation of large-scale coastal free-surface flows. The three-dimensional immersed boundary method was used for the enforcement of the no-slip boundary condition on the bed surface. The water-air interface was tracked using the level-set method. The numerical model was effectively validated against laboratory measurements involving wave propagation over a flatbed with an elliptical shoal, whose presence induces combined wave refraction and diffraction phenomena. The parallel implementation of the model enabled the efficient simulation of depth-resolved, wave-induced, three-dimensional, free-surface flow, the model parallel efficiency and strong scaling are quantitatively demonstrated.

The present study intends to investigate numerically the impact of: i) the fluid added mass, ii) the turbine rotational speed and iii) the variation of the runner blade bearing stiffness due to the turbine water head on the modal response of a reduced scale Kaplan turbine. The impact of each variable has been quantified by means of a series of numerical modal analyses of the turbine in vacuum and in water, and at rest and rotating. It has been found that the natural frequencies of the Kaplan turbine model are sensitive to all the variables investigated in the present paper, the added mass being the factor which has the greatest impact. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 814958. The authors also wish to acknowledge Vattenfall for the technical support received for developing this work.

State of the art rocket engines are reaching performance levels that have become limited by the available manufacturing techniques. With a great focus on these engines’ efficiency, rocket engine producers are focusing on increasing combustion chamber pressures and temperatures, which in turn produces increasingly greater structural and thermal loads. Complex cooling systems are usually used to tackle this issue, being the most predominant formula to use the stored cryogenic propellant as a coolant before being injected in the combustion pressure, more commonly known as regenerative cooling. However, these cooling systems are limited by the state of the art manufacturing techniques. To deal with this issue, efforts have been made to implement modern metal Additive Manufacturing (AM) techniques to rocket engine production. In order to show the extent of the benefits of such innovations, a rocket engine nozzle has been designed following the characteristics of SpaceX’s latest Raptor engines. This design has been tested through Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) simulations so as to validate its performance parameters and study how the implementation of metal AM techniques would improve the engine’s performance. The economic feasibility of such implementation has been studied through the comparison to former techniques, as well as their impact to the environment

The aerodynamic performance of active flow control on wings using synthetic jets with zero net-mass flow is investigated. The study is conducted via wall-modeled large-eddy simulations using a finiteelement-based solver. The performance of synthetic jets is evaluated for the high-lift configuration of the JAXA Standard Model at realistic Reynolds numbers for landing Rec = 1.96 × 106 . The results show that, at high angles of attack, the control successfully eliminates the laminar/turbulent recirculations located downstream the actuator, which increases the aerodynamic performance. Our efforts illustrate the technology-readiness of large-eddy simulation in the design of control strategies for real-world external aerodynamic applications. This work is funded in part by the Coturb program of the European Research Council. O. L. acknowledges the financial support by the Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain (ref. TRA2017-88508-R) and the European Union’s Horizon 2020 research and innovation programme (INFRAEDI-02-2018, EXCELLERAT- The European Centre Of Excellence For Engineering Applications H2020.). We also acknowledge Red Española de Supercomputacion and Barcelona Supercomputing Center for awarding us access to the MareNostrum IV machine based in Barcelona, Spain (FI-2018-3-0021, FI-2018-2-0015, FI-2018-1-0022, FI-2017-3-0024). A.L.-D. acknowledges the support of NASA Transformative Aeronautics Concepts Program (Grant No. NNX15AU93A) and the Office of Naval Research (Grant No. N000141712310).

Treballs Finals de Grau d'Enginyeria Química, Facultat de Química, Universitat de Barcelona, Curs: 2020-2021, Tutors: David Curcó Cantarell, Ricard Torres Castillo, As of 2021, even with growing concerns about climate change, internal combustion engines still power more than 99% of the vehicles on the planet, from the smallest of motorcycles to the largest container ships. Internal combustion engines are thermal machines subject to great irreversibilities that have peak thermal efficiencies well below 50% and thus reject large amounts of heat. As a consequence of this, they require cooling to keep their temperature below the maximum service temperature of their constitutive materials. In most modern engines, cooling is achieved through the forced circulation of a liquid coolant through the engine. The homogeneity of this refrigeration is critical as uneven cooling creates great thermal stresses that would severely reduce the durability and reliability of the engine. In this work, the cooling jacket of the cylinder on an internal combustion engine was modelized and analyzed through computational fluid dynamics simulations using the academic version of the commercial software ANSYS® Fluent®. First, a simplified model based on the cooling jacket on a single-cylinder liquid-cooled 125 cc spark-ignited engine was elaborated and validated through comparison with data available in the literature. Boundary conditions were obtained from a combination of experimental and literature data and the academic version of ANSYS® Fluent® proved being sufficient to perform a semiquantitative analysis. Once its results were validated, this system was then modified by including different combinations of baffles and additional outlets with the aim of improving its heat transfer characteristics, especially in terms of cooling homogeneity. Results were especially promising for the system containing the combination of additional outlets on the top part of the cooling jacket and a baffle on its outer wall. Uniform and enhanced cooling was achieved in the area of influence of the baffle while a notable pressure drop reduction in the cooling jacket was attributed to the presence of the additional outlets

The Material Point Method (MPM) [Sulsky et al. 1995] [1] combines a La-grangian description of a domain using a set of particles with a computational mesh used to solve numerically the system of governing equations. At each time step, the governing equations are solved on the nodes of the computa-tional grid, while history dependent variables and material information are saved on the particles for the entire deformation process. The Finite Element Method (FEM) has a counterpart which has beendeveloped in the last decades, the so called Meshless Methods (MMs) . Asa start, this project studies one of these methods, the Moving Least Squares(MLS) method, a previous step to combine it with the MPM, through Python programming language. First, it is tested in depth the MLS method for a 2D domain and its exact approximation cases for different consistency orders with different functions.It is considered either a structured or a random particle distribution, analyz-ing the optimal weight functions to be used and different dilation parameters. Next, MLS is to be applied as a solving solution for Partial Differen-tial Equation (PDE) systems for a 10x10m square domain submitted to self weight. Two cases are studied, depending on the constitutive model, one for Plane Stress and one for Stokes, being the latter a particular considera-tion of Navier-Stokes system of equations in which the convective terms areneglected in front of the viscous terms, thus for this Computational Fluid Dynamics (CFD) simulation high viscosity is implied for the momentum conservation equation. Plane Stress case is compared to the FEM case, for lateral fixed and base fixed cases, while Stokes case is only computed through MLS, being considered steady and transient cases, both for based fixed. A stabilization method for first and also for second order derivative terms is applied through Galerkin Least Squares (GLS) method. In addition, the software Comsol Multiphysics®is used as a tool to compare results obtained to an industry well-established FEM program andas a guide for the project

Numerical investigations of propagating vortex states (pVs) for ferrofluidic Couette flow with small aspect ratio and fixed non-rotating end-walls are presented. We study structural modifications and changes in spatial and temporal behavior for pV solutions. The system is subjected to either pure axial or pure transverse magnetic field, with the latter already breaking the basic system symmetries. While under axial magnetic field pVs remain basically the same, they are found to appear in various configurations with different symmetry variation in flow structure and flow dynamics under symmetry breaking transversal magnetic field. pVs appearing in a pitchfork bifurcation are found either symmetric or asymmetric/alternating, regarding the full cycle of vortex generation, propagation and annihilation, in upper and lower system half.

This study is focused on the numerical investigation of reduced chemical schemes for high pressure spray flames of oxymethylene ethers (OMEx). A reduced mechanism using Path Flux Analysis (PFA) technique is tested using an a priori and a posteriori evaluation under the ECN Spray A nominal conditions. The global flame metrics for spray A along with the flame shape are well reproduced by the reduced mechanism, which encourages its use for practical applications. The research leading to these results has received funding through the ENERXICO project from the European Union’s Horizon 2020 Programme, grant agreement n 828947, and from the Mexican Department of Energy, CONACYT-SENER Hidrocarburos grant agreement n B-S-69926 and the Spanish Ministry of Economy and Competitiveness in the frame of the CHEST project (TRA2017-89139-C2-2- R). The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (IM- 2021-1-0014, IM-2020-3-0029, IM-2020-2-0023,IM- 2020-1-0013).

In this work, consideration is given to an aerodynamic concept to boost the filtration in face masks of airborne hygroscopic particles such as those caused by an infected person when coughs or sneezes. Nowadays, increasing the filtration efficiency of face masks implies either increasing the number of crisscrossing fiber layers or decreasing the equivalent hydraulic diameter of the pore, however, both measures are in clear detriment of its breathability. Here, a novel strategy is proposed in which the filtration of an airborne particle is boosted by increasing its diameter. We called properly this concept as the aerodynamic barrier layer. In this concept, a traditional crisscrossing fiber layer is replaced by a parallel rearranged of the fibers in the direction of the flow. This rearrangement will promote central lift forces which will push the particles toward the center of the channel where after clustering they will coalesce resulting in a bigger particle that can be now easily captured by a conventional fiber crisscrossing layer. Utilizing a simplified geometrical model, an expression for the required length of the aerodynamic barrier layer was derived. It is shown that an aerodynamic barrier layer with a length of only a few millimeters can aerodynamically focus water droplets around 1 μm-diameter and the penetration of airborne particles can be reduced up to 55%.

This work provides a numerical investigations of propagating vortex flow states (pVs) for ferrofluidic Couette flow with small aspect ratio and fixed non-rotating end-walls. The system is subjected to oblique magnetic fields as superposition of axial and transverse orientated fields. Such field configuration breaks the basic system symmetries and renders all flow structures to be inherently three-dimensional with complexer flow dynamics. Under oblique field configuration pV states are not direct present at onset. Instead oscillating flow states (oVs) bifurcate out of the stationary state. Basically these oVs hold same symmetries as pVs, which eventually evolve in a smooth transformation out of the oVs. pVs under oblique fields appear periodic or quasi-periodic, which render them topological speaking to exist on either two- or one-dimensional invariant manifolds as 2-torus or limit cycle (1-torus) solutions, respectively. In detail, structural modifications and changes in spatial and temporal behavior for pV solutions are studied with changing the magnetic field strength of the applied magnetic field.

The existence of triadic resonances in the magnetized spherical Couette system (MSC) is related to the development of modulated rotating waves, which are quasiperiodic flows understood in terms of bifurcation theory in systems with symmetry. In contrast to previous studies in spherical geometry the resonant modes are not inertial waves but related with the radial jet instability which is strongly equatorially antisymmetric. We propose a general framework in which triadic resonances are generated through successive Hopf bifurcations from the base state. The study relies on an accurate frequency analysis of different modes of the flow, for solutions belonging to two different bifurcation scenarios. The azimuthal and latitudinal nonlinear coupling among the resonant modes is analysed and interpreted using spherical harmonics and the results are compared with previous studies in spherical geometry., 15 pages, 10 figures, 3 tables

We conduct magnetized spherical Couette (MSC) flow experiments in the return flow instability regime with GaInSn as the working fluid, the ratio of the inner to the outer sphere radii ri/ro = 0.5, the Reynolds number Re = 1000, and the Hartmann number Ha ¿ [27.5, 40]. Rotating waves with different azimuthal wavenumbers m ¿ {2, 3, 4} manifest in certain ranges of Ha in the experiments, depending on whether the values of Ha were fixed or varied from different initial values. These observations demonstrate the multistability of rotating waves, which we attribute to the dynamical system representing the state of the MSC flow tending to move along the same solution branch of the bifurcation diagram when Ha is varied. In experiments with both fixed and varying Ha, the rotation frequencies of the rotating waves are consistent with the results of nonlinear stability analysis. A brief numerical investigation shows that differences in the azimuthal wavenumbers of the rotating waves that develop in the flow also depend on the azimuthal modes that are initially excited.

An analysis of existing and newly derived fast-projection methods for the numerical integration of incompressible Navier&ndash, Stokes equations is proposed. Fast-projection methods are based on the explicit time integration of the semi-discretized Navier&ndash, Stokes equations with a Runge&ndash, Kutta (RK) method, in which only one Pressure Poisson Equation is solved at each time step. The methods are based on a class of interpolation formulas for the pseudo-pressure computed inside the stages of the RK procedure to enforce the divergence-free constraint on the velocity field. The procedure is independent of the particular multi-stage method, and numerical tests are performed on some of the most commonly employed RK schemes. The proposed methodology includes, as special cases, some fast-projection schemes already presented in the literature. An order-of-accuracy analysis of the family of interpolations here presented reveals that the method generally has second-order accuracy, though it is able to attain third-order accuracy only for specific interpolation schemes. Applications to wall-bounded 2D (driven cavity) and 3D (turbulent channel flow) cases are presented to assess the performances of the schemes in more realistic configurations.

Petrographic and geochemical analyses (δ18O, δ13C, 87Sr/86Sr, clumped isotopes, and elemental composition) coupled with field structural data of synkinematic calcite veins, fault rocks, and host rocks are used to reconstruct the episodic evolution of an outstanding exposed thrust zone in the Southern Pyrenees and to evaluate the fault behavior as a conduit or barrier to fluid migration. The selected thrust displaces the steeply dipping southern limb of the Sant Corneli-Bóixols anticline, juxtaposing a Cenomanian-Turonian carbonate unit against a Coniacian carbonate sequence. Successive deformation events are recorded by distinct fracture systems and related calcite veins, highlighting (i) an episodic evolution of the thrust zone, resulting from an upward migration of the fault tip (process zone development) before growth of the fault (thrust slip plane propagation), and (ii) compartmentalization of the thrust fault zone, leading to different structural and fluid flow histories in the footwall and hanging wall. Fractures within the footwall comprise three systematically oriented fracture sets (F1, F2, and F3), each sealed by a separate generation calcite cement, and a randomly oriented fracture system (mosaic to chaotic breccia), cemented by the same cements as fracture sets F1 and F2. The formation of fractures F1 and F2 and the mosaic to chaotic breccia is consistent with dilatant fracturing within the process zone (around the fault tip) during initial fault growth, whereas the formation of the latest fracture system points to hybrid shear-dilational failure during propagation of the fault. The continuous formation of different fracture systems and related calcite cementation phases evidences that the structural permeability in the footwall was transient and that the fluid pathways and regime evolved due to successive events of fracture opening and calcite cementation. Clumped isotopes evidence a progressive increase in precipitation temperatures from around 50°C to 117°C approximately, interpreted as burial increase linked to thrust sheet emplacement. During this period, the source of fluid changed from meteoric fluids to evolved meteoric fluids due to the water-rock interaction at increasing depths and temperatures. Contrary to the footwall, within the hanging wall, only randomly oriented fractures are recognized and the resulting crackle proto-breccia is sealed by a later and different calcite cement, which is also observed in the main fault plane and in the fault core. This cement precipitated from formation fluids, at around 95°C, that circulated along the fault core and in the hanging wall block, again supporting the interpretation of compartmentalization of the thrust structure. The integration of these data reveals that the studied thrust fault acted as a transverse barrier, dividing the thrust zone into two separate fluid compartments, and a longitudinal drain for migration of fluids. This study also highlights the similarity in deformation processes and mechanisms linked to the evolution of fault zones in compressional and extensional regimes involving carbonate rocks., This research was carried out within the framework of the Dirección General de Investigación Científica y Técnica Spanish Project (PGC2018-093903-B-C22) (Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, Unión Europea) and the Grup Consolidat de Recerca “Geologia Sedimentària” (2017-SGR-824). The PhD research of DM-L is supported by the FPI2016 (BES-2016-077214) Spanish program from MINECO.