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Frontiers of computational fluid dynamics (CFD) are constantly expanding and eagerly demanding more computational resources. Currently, we are experiencing an rapid evolution in the high performance computing systems driven by power consumption constraints. New HPC nodes incorporate accelerators that are used as math co-processors for increasing the throughput and the FLOP per watt ratio. On the other hand, multi-core CPUs have turned into energy efficient system-on-chip architectures. By doing so, the main components of the node are fused and integrated into a single chip reducing the energy costs. Nowadays, several institutions and governments are investing in the research and development of different aspects of HPC that could lead to the next generations of supercomputers. This initiatives have entitled the problem as the exascale challenge. This goal can only be achieved by incorporating major changes in computer architecture, memory design and network interfaces. The CFD community faces an important challenge: keep the pace at the rapid changes in the HPC resources. The codes and formulations need to be re-design in other to exploit the different levels of parallelism and complex memory hierarchies of the new heterogeneous systems. The main characteristics demanded to the new CFD software are: memory awareness, extreme concurrency, modularity and portability. This thesis is devoted to the study of a CFD algorithm re-factoring for the adoption of new technologies. Our application context is the solution of incompressible flows (DNS or LES) on unstructured meshes. The first approach was using GPUs for accelerating the Poisson solver, that is the most computational intensive part of our application. The positive results obtained in this first step motivated us to port the complete time integration phase of our application. This requires a major redesign of the code. We propose a portable implementation model for CFD applications. The main idea was substituting stencil data structures and kernels by algebraic storage formats and operators. By doing so, the algorithm was restructured into a minimal set of algebraic operations. The implementation strategy consisted in the creation of a low-level algebraic layer for computations on CPUs and GPUs, and a high-level user-friendly discretization layer for CPUs that is fully localized at the preprocessing stage where performance does not play an important role. As a result, at the time-integration phase the code relies only on three algebraic kernels: sparse-matrix-vector product (SpMV), linear combination of two vectors (AXPY) and dot product (DOT). Such a simple set of basic linear algebra operations naturally provides the desired portability to any computing architecture. Special attention was paid at the development of data structures compatibles with the stream processing model. A detailed performance analysis was studied in both sequential and parallel execution engaging up to 128 GPUs in a hybrid CPU/GPU supercomputer. Moreover, we tested the portable implementation model of TermoFluids code in the Mont-Blanc mobile-based supercomputer. The re-design of the kernels exploits a heterogeneous execution model using both computing devices CPU and GPU of the ARM-based nodes. The load balancing between the two computing devices exploits a tabu search strategy that tunes the workload distribution during the preprocessing stage. A comparison of the Mont-Blanc prototypes with high-end supercomputers in terms of the achieved net performance and energy consumption provided some guidelines of the behavior of CFD applications in ARM-based architectures. Finally, we present a memory aware auto-tuned Poisson solver for problems with one Fourier diagonalizable direction. This work was developed and tested in the BlueGene/Q Vesta supercomputer, and aims at demonstrating the relevance of vectorization and memory awareness for fully exploiting the modern energy efficient CPUs. ; Las fronteras de la dinámica de fluidos computacional (CFD) están en constante expansión y demandan más y más recursos computacionales. Actualmente, estamos experimentando una evolución en los sistemas de computación de alto rendimiento (HPC) impulsado por restricciones de consumo de energía. Los nuevos nodos HPC incorporan aceleradores que se utilizan como co-procesadores para incrementar el rendimiento y la relación FLOP por vatio. Por otro lado, CPUs multi-core se han convertido en arquitecturas system-on-chip. Hoy en día, varias instituciones y gobiernos están invirtiendo en la investigación y desarrollo de los diferentes aspectos de HPC que podrían llevar a las próximas generaciones de superordenadores. Estas iniciativas han titulado el problema como el "exascale challenge". Este objetivo sólo puede lograrse mediante la incorporación de cambios importantes en: la arquitectura de ordenador, diseño de la memoria y las interfaces de red. La comunidad de CFD se enfrenta a un reto importante: mantener el ritmo a los rápidos cambios en las infraestructuras de HPC. Los códigos y formulaciones necesitan ser rediseñados para explotar los diferentes niveles de paralelismo y complejas jerarquías de memoria de los nuevos sistemas heterogéneos. Las principales características exigidas al nuevo software CFD son: estructuras de datos, la concurrencia extrema, modularidad y portabilidad. Esta tesis está dedicada al estudio de un modelo de implementation CFD para la adopción de nuevas tecnologías. Nuestro contexto de aplicación es la solución de los flujos incompresibles (DNS o LES) en mallas no estructuradas. El primer enfoque se basó en utilizar GPUs para acelerar el solver de Poisson. Los resultados positivos obtenidos en este primer paso nos motivaron a la portabilidad completa de la fase de integración temporal de nuestra aplicación. Esto requiere un importante rediseño del código. Proponemos un modelo de implementacion portable para aplicaciones de CFD. La idea principal es sustituir las estructuras de datos de los stencils y kernels por formatos de almacenamiento algebraicos y operadores. La estrategia de implementación consistió en la creación de una capa algebraica de bajo nivel para los cálculos de CPU y GPU, y una capa de discretización fácil de usar de alto nivel para las CPU. Como resultado, la fase de integración temporal del código se basa sólo en tres funciones algebraicas: producto de una matriz dispersa con un vector (SPMV), combinación lineal de dos vectores (AXPY) y producto escalar (DOT). Además, se prestó especial atención en el desarrollo de estructuras de datos compatibles con el modelo stream processing. Un análisis detallado de rendimiento se ha estudiado tanto en ejecución secuencial y paralela utilizando hasta 128 GPUs en un superordenador híbrido CPU / GPU. Por otra parte, hemos probado el nuevo modelo de TermoFluids en el superordenador Mont-Blanc basado en tecnología móvil. El rediseño de las funciones explota un modelo de ejecución heterogénea utilizando tanto la CPU y la GPU de los nodos basados en arquitectura ARM. El equilibrio de carga entre las dos unidades de cálculo aprovecha una estrategia de búsqueda tabú que sintoniza la distribución de carga de trabajo durante la etapa de preprocesamiento. Una comparación de los prototipos Mont-Blanc con superordenadores de alta gama en términos de rendimiento y consumo de energía nos proporcionó algunas pautas del comportamiento de las aplicaciones CFD en arquitecturas basadas en ARM. Por último, se presenta una estructura de datos auto-sintonizada para el solver de Poisson en problemas con una dirección diagonalizable mediante una descomposicion de Fourier. Este trabajo fue desarrollado y probado en la superordenador BlueGene / Q Vesta, y tiene por objeto demostrar la relevancia de vectorización y las estructuras de datos para aprovechar plenamente las CPUs de los superodenadores modernos. ; Postprint (published version)

The theoretical models of Batchelor and Kraichnan, which account for the smallest scales of a scalar field passively advected by a turbulent fluid (Prandtl . 1), have been validated using shear and temperature profiles measured with a microstructure profiler in a lake. The value of the rate of dissipation of turbulent kinetic energy « has been computed by fitting the shear spectra to the Panchev and Kesich theoretical model and the one-dimensional spectra of the temperature gradient, once « is known, to the Batchelor and Kraichnan models and from it determining the value of the turbulent parameter q. The goodness of the fit between the spectra corresponding to these models and the measured data shows a very clear dependence on the degree of isotropy, which is estimated by the Cox number. The Kraichnan model adjusts better to themeasured data than the Batchelor model, and the values of the turbulent parameter that better fit the experimental data are qв 5 4.4 ± 0.8 and qK 5 7.9± 2.5 for Batchelor and Kraichnan, respectively, when Cox ≥ 50. Once the turbulent parameter is fixed, a comparison of the value of « determined from fitting the thermal gradient spectra to the value obtained after fitting the shear spectra shows that the Kraichnan model gives a very good estimate of the dissipation, which the Batchelor model underestimates ; This research was developed under Spanish Government Project FIS2008-03608. We would also like to thank Francesc Nogue´ (University of Girona) for his electronic engineering support and Joan Corominas (Banyoles) for his sailing support

The theoretical models of Batchelor and Kraichnan, which account for the smallest scales of a scalar field passively advected by a turbulent fluid (Prandtl . 1), have been validated using shear and temperature profiles measured with a microstructure profiler in a lake. The value of the rate of dissipation of turbulent kinetic energy « has been computed by fitting the shear spectra to the Panchev and Kesich theoretical model and the one-dimensional spectra of the temperature gradient, once « is known, to the Batchelor and Kraichnan models and from it determining the value of the turbulent parameter q. The goodness of the fit between the spectra corresponding to these models and the measured data shows a very clear dependence on the degree of isotropy, which is estimated by the Cox number. The Kraichnan model adjusts better to themeasured data than the Batchelor model, and the values of the turbulent parameter that better fit the experimental data are qв 5 4.4 ± 0.8 and qK 5 7.9± 2.5 for Batchelor and Kraichnan, respectively, when Cox ≥ 50. Once the turbulent parameter is fixed, a comparison of the value of « determined from fitting the thermal gradient spectra to the value obtained after fitting the shear spectra shows that the Kraichnan model gives a very good estimate of the dissipation, which the Batchelor model underestimates ; This research was developed under Spanish Government Project FIS2008-03608. We would also like to thank Francesc Nogue´ (University of Girona) for his electronic engineering support and Joan Corominas (Banyoles) for his sailing support

The theoretical models of Batchelor and Kraichnan, which account for the smallest scales of a scalar field passively advected by a turbulent fluid (Prandtl . 1), have been validated using shear and temperature profiles measured with a microstructure profiler in a lake. The value of the rate of dissipation of turbulent kinetic energy « has been computed by fitting the shear spectra to the Panchev and Kesich theoretical model and the one-dimensional spectra of the temperature gradient, once « is known, to the Batchelor and Kraichnan models and from it determining the value of the turbulent parameter q. The goodness of the fit between the spectra corresponding to these models and the measured data shows a very clear dependence on the degree of isotropy, which is estimated by the Cox number. The Kraichnan model adjusts better to themeasured data than the Batchelor model, and the values of the turbulent parameter that better fit the experimental data are qв 5 4.4 ± 0.8 and qK 5 7.9± 2.5 for Batchelor and Kraichnan, respectively, when Cox ≥ 50. Once the turbulent parameter is fixed, a comparison of the value of « determined from fitting the thermal gradient spectra to the value obtained after fitting the shear spectra shows that the Kraichnan model gives a very good estimate of the dissipation, which the Batchelor model underestimates ; This research was developed under Spanish Government Project FIS2008-03608. We would also like to thank Francesc Nogue´ (University of Girona) for his electronic engineering support and Joan Corominas (Banyoles) for his sailing support

Turbidity, CTD, and temperature and shear microstructure data recorded along a 25 km transect from 8 to 69 m depth across the Ebro Delta shelf (northwestern Mediterranean) are presented. The water column was stratified and prior to the campaign the regional southwest flow was measured to have superimposed diurnal and sub-inertial components. The bottom boundary layer (BBL) at all stations deeper than 20 m has a vertical extension of 3 to 9 m, increasing to 12 m at the deeper stations and even to 14 m at a station at 45 m depth outside the studied transect. The law of the wall was identified at almost all stations with an extension ranging from 40% to 100% of that of the BBL. At some stations high dissipation rates were found in the interior of the bottom layer. The study shows the correspondence between the turbidity contents and the local mixing processes at the BBL and suggests that sub-critical reflection of internal waves could play an important role in boundary mixing. Our data also suggest that during the campaign, after two consecutive short episodes of high winds, the first baroclinic mode shifted to the second one ; We are grateful to M. Demestre for allowing us to be on board the Garcia de Cid within the context of the VEDA Project and the EU RESPONSE (Q5RS-2002- 00787) project and for facilitating the measurements. We are also very grateful to the editor and the anonymous reviewers, whose comments have helped to improve the first version of the paper. I. Lozovatsky and M Muñiz collaborated on the data analysis at an initial stage of this work. This paper was finished in accordance with the objectives of the project CGL2008-03608 funded by the Ministry of Science and Innovation of the Spanish Government and within the framework of the CLIMSEAS Project (FP7-PEOPLE-2009-IRSES N. 247512)

Turbidity, CTD, and temperature and shear microstructure data recorded along a 25 km transect from 8 to 69 m depth across the Ebro Delta shelf (northwestern Mediterranean) are presented. The water column was stratified and prior to the campaign the regional southwest flow was measured to have superimposed diurnal and sub-inertial components. The bottom boundary layer (BBL) at all stations deeper than 20 m has a vertical extension of 3 to 9 m, increasing to 12 m at the deeper stations and even to 14 m at a station at 45 m depth outside the studied transect. The law of the wall was identified at almost all stations with an extension ranging from 40% to 100% of that of the BBL. At some stations high dissipation rates were found in the interior of the bottom layer. The study shows the correspondence between the turbidity contents and the local mixing processes at the BBL and suggests that sub-critical reflection of internal waves could play an important role in boundary mixing. Our data also suggest that during the campaign, after two consecutive short episodes of high winds, the first baroclinic mode shifted to the second one ; We are grateful to M. Demestre for allowing us to be on board the Garcia de Cid within the context of the VEDA Project and the EU RESPONSE (Q5RS-2002- 00787) project and for facilitating the measurements. We are also very grateful to the editor and the anonymous reviewers, whose comments have helped to improve the first version of the paper. I. Lozovatsky and M Muñiz collaborated on the data analysis at an initial stage of this work. This paper was finished in accordance with the objectives of the project CGL2008-03608 funded by the Ministry of Science and Innovation of the Spanish Government and within the framework of the CLIMSEAS Project (FP7-PEOPLE-2009-IRSES N. 247512)

Turbidity, CTD, and temperature and shear microstructure data recorded along a 25 km transect from 8 to 69 m depth across the Ebro Delta shelf (northwestern Mediterranean) are presented. The water column was stratified and prior to the campaign the regional southwest flow was measured to have superimposed diurnal and sub-inertial components. The bottom boundary layer (BBL) at all stations deeper than 20 m has a vertical extension of 3 to 9 m, increasing to 12 m at the deeper stations and even to 14 m at a station at 45 m depth outside the studied transect. The law of the wall was identified at almost all stations with an extension ranging from 40% to 100% of that of the BBL. At some stations high dissipation rates were found in the interior of the bottom layer. The study shows the correspondence between the turbidity contents and the local mixing processes at the BBL and suggests that sub-critical reflection of internal waves could play an important role in boundary mixing. Our data also suggest that during the campaign, after two consecutive short episodes of high winds, the first baroclinic mode shifted to the second one ; We are grateful to M. Demestre for allowing us to be on board the Garcia de Cid within the context of the VEDA Project and the EU RESPONSE (Q5RS-2002- 00787) project and for facilitating the measurements. We are also very grateful to the editor and the anonymous reviewers, whose comments have helped to improve the first version of the paper. I. Lozovatsky and M Muñiz collaborated on the data analysis at an initial stage of this work. This paper was finished in accordance with the objectives of the project FIS2008-03608 funded by the Ministry of Science and Innovation of the Spanish Government and within the framework of the CLIMSEAS Project (FP7-PEOPLE-2009-IRSES N. 247512)

The leukocyte-specific ß2-integrin LFA-1 and its ligand ICAM-1, expressed on endothelial cells (ECs), are involved in the arrest, adhesion, and transendothelial migration of leukocytes. Although the role of mechanical forces on LFA-1 activation is well established, the impact of forces on its major ligand ICAM-1 has received less attention. Using a parallel-plate flow chamber combined with confocal and super-resolution microscopy, we show that prolonged shear flow induces global translocation of ICAM-1 on ECs upstream of flow direction. Interestingly, shear forces caused actin rearrangements and promoted actin-dependent ICAM-1 nanoclustering before LFA-1 engagement. T cells adhered to mechanically prestimulated ECs or nanoclustered ICAM-1 substrates developed a promigratory phenotype, migrated faster, and exhibited shorter-lived interactions with ECs than when adhered to non mechanically stimulated ECs or to monomeric ICAM-1 substrates. Together, our results indicate that shear forces increase ICAM-1/LFA-1 bonds because of ICAM-1 nanoclustering, strengthening adhesion and allowing cells to exert higher traction forces required for faster migration. Our data also underscore the importance of mechanical forces regulating the nanoscale organization of membrane receptors and their contribution to cell adhesion regulation. ; The authors thank T. van Zanten, E. Gutierrez and F. Campelo for useful discussions, J. Andilla from the SLN facility at ICFO for his support with STED imaging, and M. Rivas for technical assistance. This work was supported by the Human Frontiers Science Program (HFSP) (GA RGP0027/2012) and European Union H2020 Framework Programme under European Research Council Grant 788546 – NANO-MEMEC. M.F.G.-P. acknowledges support from the Government of Spain (FIS2017-89560-R; Severo Ochoa CEX2019-000910-S), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya (CERCA, AGAUR Grant No. 2017SGR1000). I.K.P. acknowledges the support of the Grant No. POIR.04.04.00-00-3F2E/17- 00 which is carried out ...

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). ; Peer Reviewed ; Postprint (published version)

Este texto analiza la importancia de la técnica de las ecuaciones diferenciales y sus planos de fases para expresar las conductas de un sistema, claro esto no sería un modelo exacto pero puede mostrarnos cualitativamente el curso de los acontecimientos en lo que respecta al mercado cambiario.

Fluidic oscillators are often used to modify the forces fluid generates on any given bluff body; they can also be used as flow, pressure or acoustic sensors, with each application requiring a particular oscillator configuration. Regarding the fluidic oscillators' main performance, a problem which is not yet clarified is the understanding of the feedback channel effect on the oscillator outlet mass flow frequency and amplitude, especially under compressible flow conditions. In order to bring light to this point, a set of three-dimensional Direct Numerical Simulations under compressible flow conditions are introduced in the present paper; four different feedback channel lengths and two inlet Reynolds numbers Re = 12,410 and Re = 18,617 are considered. From the results obtained, it is observed that as the inlet velocity increases, the fluidic oscillator outlet mass flow frequency and amplitude increase. An increase of the feedback channel length decreases the outlet mass flow oscillating frequency. At large feedback channel lengths, the former main oscillation tends to disappear, the jet inside the mixing chamber simply fluctuates at high frequencies. Once the Feedback Channel (FC) length exceeds a certain threshold, the oscillation stops. Under all conditions studied, pressure waves are observed to be traveling along the feedback channels, their origin and interaction with the jet entering the mixing chamber are thoroughly evaluated. The paper proves that jet oscillations are pressure-driven ; This work was supported by the Spanish and Catalan Governments under grants FIS2016- 77849-R and 2017-SGR-00785, respectively. The computations were done at the Barcelona Supercomputing Center under grants FI-2018-3-0036 and FI-2019-1-0017 ; Postprint (published version)

We investigate the aerodynamic performance of active flow control of airfoils and wings using synthetic jets with zero net-mass flow. The study is conducted via wall-resolved and wall-modeled large-eddy simulation using two independent CFD solvers: Alya, a finite-element- based solver; and charLES, a finite-volume-based solver. Our approach is first validated in a NACA4412, for which numerical and experimental results are already available in the literature. The performance of synthetic jets is evaluated for two flow configurations: a SD7003 airfoil at moderate Reynolds number with laminar separation bubble, which is representative of Micro Air Vehicles, and the high-lift configuration of the JAXA Standard Model at realistic Reynolds numbers for landing. In both cases, our predictions indicate 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 Supercomputación 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). We acknowledge Prof. R. Vinuesa for the discussions and data analysis of the NACA4412. A.L.-D. acknowledges the support of NASA Transformative Aeronautics Concepts Program (Grant No. NNX15AU93A) and the Office of Naval Research (Grant No. N000141712310). ; Peer Reviewed ; Postprint (published version)