Search

We describe the implementation of several recently developed boundary layer transition models into the overset computational fluid dynamics code, REX, developed at the University of Iowa, together with an evaluation of its capabilities and limitations for naval hydrodynamics applications. Models based on correlations and on amplification factor transport were implemented in one- and two-equation Reynolds-averaged Navier-Stokes turbulence models, including modifications to operate in crossflow. Extensive validation of the transition models implemented in REX is performed for several 2- and 3-dimensional geometries of naval relevance. Standard tests with extensive available experimental data include flat plates in zero pressure gradient, an airfoil, and sickle wing. More complex test cases include the propeller, P4119, with some experimental data available, and the generic submersible, Joubert BB2, with no relevant experimental data available, to validate the transition models. Simulations for these last two cases show that extensive regions of laminar flow can be present on the bodies at laboratory scale and field scale for small vessels, and the potential effects on resistance and propulsion can be significant. 1. Introduction Progress for prediction of attached, fully turbulent flows for practical aerodynamic and hydrodynamic applications has reached a relatively mature plateau. However, according to a recent comprehensive review of pacing items (Slotnick et al. 2014), the single largest hurdle for incorporating computational fluid dynamics (CFD) into the design process in the near future is the ability to accurately predict turbulent flows with boundary layer transition and separation. Transition can impact skin friction, heat transfer, noise, propulsion efficiency, and maneuverability. This is especially true at model scale and for small craft such as unmanned or autonomous surface and underwater vehicles.

In this study, we presented the influence of nanoparticle coatings over the inner furnace wall used in TS-FF-AAS for the determination of trace elements (Ag, Cd, Pb, and Se) in different complex matrix. The use of ceramic nanomaterials (ZrO2 and TiO2) as a coating, produced by the dipcoating technique, enabled enhanced analytical performance (analytical response, sensitivity, LOD, LOQ, and signal stability). This furnace modification was used for determining the analytes in different samples. Fil: Carrone, Guillermo Alejandro. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentina Fil: Onna, Diego Ariel. Universidad Nacional de San Martin. Instituto de Nanosistemas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Morzan, Ezequiel Martin. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Candal, Roberto Jorge. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentina Fil: Minaberry, Yanina Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Schneider, J.. Universidad de Belgrano. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Tudino, Mabel Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

The debonding process at the interface of filler-matrix is studied. The relevance of this process lays in its triggering effect of toughening mechanisms in polymer based composites. Based on a micromechanical model, a general approach of the debonding condition was derived. The proposed expression was applied for different particle shapes: spherical, ellipsoid, cubic, rectangular and fiber. Results of debonding strength versus geometric parameters of the different particles showed that oblate ellipsoids and cubic particles can be easily analyzed as spherical filler. Fil: Perez, Ezequiel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial. Centro de Plástico; Argentina Fil: Lauke, B.. Leibniz-institut Für Polymerforschung Dresden; Alemania

In this work we present a proof of concept for the optimization of the analytical performance in ThermoSpray Flame Furnace Atomic Absorption Spectrometry (TS-FFAAS) by using different systems of sample injection. The influence of different operational variables was studied with emphasis on the characteristics of the ceramic capillary employed for sample introduction. The classic single hole capillary was compared to capillaries with different number of inner holes (one, four and six) and different spatial distribution. The influence on the analytical signal of a double simultaneous injection applied to different zones of the atomization furnace was also evaluated. Determination of elements with different atomization temperature (Ag, Cd and Se) was done, results shown an optimization of the figures of merit with respect to the TS-FF-AAS conventional assembly increased with the element volatility. Applications of Multi Injection (MI-TS-FF-AAS) was evaluated for determination of Cd in “yerba mate” samples; comparison of the obtained results using the proposed technique with other validated ones showed good agreement, and a reduction of amount of sample for the determination was achieved by using the multi-injection alternative. A discussion focused on the importance of an efficient sample introduction on the figures of merit attainable with TS-FFAAS and analytical applications of the technique is provided.

In this work we present the use of EMFAAS (Electrothermal Metallic Furnace Atomic Absorption Spectroscopy) for the determination of Cd in the tobacco cigarettes of five commercial brands. Optimization of the experimental conditions was done by controlling the sample flow rate and the temperature of both the injection capillary and the atomization cell. The determination was made in the whole cigarettes, filters and ashes of the cigarettes once consumed, cases in which the Cd concentration is much lower and its quantification is more difficult. For the validation of the results, the ICP-OES technique was used, obtaining good agreement within the experimental error. The results show that EMFAAS is a promising tool for the determination of volatile analytes. Fil: Carrone, Guillermo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Morzan, Ezequiel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Tudino, Mabel Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Etchenique, Roberto Argentino. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

In this work, films and fibers of Polypropylene based composites reinforced with quartz were investigated. The materials were processed in a twin screw extruder with filler contents of 1, 2.5, and 5 wt%. Morphology, thermal properties, and mechanical behavior of these materials were studied. A homogeneous filler dispersion and particle alignment in the extrusion direction was detected for the films. Thermograms displayed a marginal nucleating effect of quartz particles. Uniaxial tensile tests indicated a high ductility level and strain hardening for the composites processed as films (in the extrusion direction). Single fiber tests displayed improved tensile properties compared with the same materials produced as films. Quasi-static fracture tests showed a completely ductile behavior for the films in the extrusion direction. In addition, films fracture toughness was found to increase with filler content. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Polypropylene (PP) composites with 5 wt% of different rigid particles (Al2O3 nanoparticles, SiO2 nanoparticles, Clay (Cloisite 20A) nanoparticles or CaCO3 microparticles) were obtained by melt mixing. Composites with different CaCO3 content were also prepared. The effect of fillers, filler content and addition of maleic anhydride grafted PP (MAPP) on the composites fracture and failure behavior was investigated. For PP/CaCO3 composites, an increasing trend of stiffness with filler loading was found while a decreasing trend of strength, ductility and fracture toughness was observed. The addition of MAPP was beneficial and detrimental to strength and ductility, respectively mainly as a result of improved interfacial adhesion. For the composites with 5 wt% of CaCO3 or Al2O3, no significant changes in tensile properties were found due to the presence of agglomerated particles. However, the PP/CaCO3 composite exhibited the best tensile behavior: the highest ductility while keeping the strength and stiffness of neat PP. In general, the composites with SiO2 or Clay, on the other hand, displayed worse tensile strength and ductility. These behaviors could be probably related to the filler ability as nucleating agent. In addition, although the incorporation of MAPP led to improved filler dispersion, it was damaging to the material fracture behavior for the composites with CaCO3, Al2O3 or Clay, as a result of a higher interfacial adhesion, the retardant effect of MAPP on PP nucleation and the lower molecular weight of the PP/MAPP blend. The PP/MAPP/SiO2 composite, on the other hand, showed slightly increased toughness respect to the composite without MAPP due to the beneficial concomitant effects of the presence of some amount of the β crystalline phase of PP and the better filler dispersion promoted by the coupling agent which favor multiple crazing. From modeling of strength, the effect of MAPP on filler dispersion and interfacial adhesion in the PP/CaCO3 composites was confirmed. Fil: Perez, Ezequiel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernandez Long"; Argentina; Fil: Alvarez, Vera Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina; Fil: Pérez, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina; Fil: Bernal, Celina Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernandez Long"; Argentina

In the present work, composites based on a commercial starch/PCL blend (MaterBi-Z) reinforced with three different nanoclays: natural montmorillonite (Cloisite Na+ (MMT)) and two modified montmorillonites (Cloisite 30B (C30B) and Cloisite 10A (C10A)) were prepared in an intensive mixer. The aim of this investigation was to determine the effect of the different nanoclays on the quasi-static fracture behavior of MaterBi-Z nanocomposites. An improvement in the fracture behavior for the composite with low contents of C30B was obtained, probably due to the easy debonding of clay achieved from a relatively weak filler–matrix interaction. On the other hand, a strong interaction had a detrimental effect on the material fracture toughness for the MaterBi-Z/C10A composites as a result of the higher compatibility of this organo-modified clay with the hydrophobic matrix. Intermediate values of fracture toughness, determined using the J-integral approach (Jc), were found for the composites with MMT due to its intermediate interaction with the matrix. The different filler–matrix interactions observed were also confirmed from the application of Pukánszky and Maurer model. In addition, multifractal analysis was applied to describe the topography of fracture surfaces. Thus, the complex fracture process could be successfully described by both experimental and theoretical tools. The obtained results suggest that it is possible to tailor the mechanical properties of the studied composites taking into account their further application. Fil: Perez, Ezequiel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernandez Long"; Argentina; Fil: Pérez, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina; Fil: Alvarez, Vera Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Universidad Nacional de Mar del Plata; Argentina; Fil: Bernal, Celina Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernandez Long"; Argentina

Polypropylene/wood flour composites with different fibre content were prepared. The effect of composition and the incorporation of maleinated polypropylene on the materials tensile and fracture and failure behaviour was investigated. Reliable fracture toughness data that will be useful for structural applications were obtained. In unmodified composites an increase in Young´s modulus was found with the addition of wood flour to PP, whereas tensile strength, strain at break and fracture toughness were observed to decrease as fibre content increased. The presence of MAPP was beneficial to tensile strength and ductility and had no significant effect on fracture toughness, as a result of enhanced fibre dispersion within the matrix and improved interfacial adhesion. Although reduced ductility and toughness were observed for the composites respect to the matrix, in the case of modified composites, environmentally friendly stiffer materials were obtained with cost saving without sacrificing strength.

Multifractal analyses were performed to elucidate the effect of incorporating maleic anhydride grafted polypropylene (MAPP) into a Polypropylene matrix: (i) on the dispersion of CaCO3 particles and (ii) on the fracture morphology of tensile samples. The box-counting method was applied considering the number of particles and the mean gray value distribution as measured properties of composites. The dispersion analysis exhibited, for the composite with MAPP, a reduction of larger agglomerates sizes without variation of the most frequent size. Similar results were achieved by a typical particle size distribution. Moreover, the morphology of fractured surfaces showed an irregular topography for composites without MAPP suggesting a complex fracture process. Composites with MAPP, on the contrary, displayed a regular surface morphology suggesting a more regular fracture process with an important reduction of ductile mechanisms. This fracture behavior was related to the variation of the singularity width Δα. The results obtained suggest that multifractal theory can be applied to elucidate the relationship between structure and mechanical behavior of PP–CaCO3 composite materials. Fil: Perez, Ezequiel Martin. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Bernal, Celina Raquel. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Piacquadio, Maria Natividad. Universidad de Buenos Aires. Facultad de Ingeniería; Argentina

In the present work, the mechanical performance of polylactic acid (PLA) based composites reinforced with hydroxyapatite (HA) or β-tricalcium phosphate (β-TCP) was investigated. The polymer was melt compounded with 1 and 2.5 wt% of particles by using an intensive mixer or a twin screw extruder. Morphological, thermal and rheological studies were performed to analyze the composites internal structure and filler-matrix interaction. The mechanical behavior was investigated through uniaxial tensile and quasi-static fracture tests. The different characterization techniques evidenced a better filler dispersion for composites obtained by extrusion independently of the filler used. A relatively weak filler-matrix interaction was revealed from morphological observations and rheological measurements. In addition, thermal analysis evidenced similar crystalline structure for all of the investigated materials. In general, uniaxial tensile parameters displayed almost constant values independently of the filler content or compounding method. Particularly, extruded composites with 2.5 wt% filler exhibited slightly increased ductility respect to neat PLA which was related to improved filler dispersion. The PLA matrix displayed load-displacement curves with ductile instability in quasi-static fracture tests. On the other hand, the composites with 2.5 wt% filler exhibited an increased stable crack growth followed by ductile instability. The fracture process was quantitatively described by means of critical stress intensity factor (K IQ) and strain energy release rate at propagation (G CP) parameters. The extruded composites with 2.5 wt% filler displayed improved propagation fracture toughness. Based on fractured surfaces analysis this enhanced behavior, not largely reported for untreated rigid fillers, was attributed to the effective activation of the toughening mechanisms of particle debonding and subsequent plastic void growth. Fil: Pérez, Claudio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Eisenberg, Patricia. Instituto Nacional de Tecnología Industrial; Argentina Fil: Bernal, Celina Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnología en Polímeros y Nanotecnología. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnología en Polímeros y Nanotecnología; Argentina Fil: Perez, Ezequiel Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnología en Polímeros y Nanotecnología. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnología en Polímeros y Nanotecnología; Argentina

A novel method for combined particle image velocimetry and laser induced fluorescence is described and results from an experiment in a stratified flow are presented. A standard two-dimensional, one camera particle image velocimetry configuration is used, acquiring images of the seeding particles and the dye marking the current simultaneously and separating the two fields digitally. The implementation of the postprocessing method, its capabilities and the necessary conditions for its use are discussed in detail. The proposed method is applied to an arrested density current front. The front is made stationary by opposing a uniform velocity profile, obtained from the combination of a moving floor and the recirculation of fresh water in the channel. To improve the quality of the images, the current is made optically homogeneous by matching the refractivity index throughout the domain. Instantaneous and time averaged fields are obtained for both velocity and density. Simultaneous measurements of these fields provide insight in the mixing processes at the front of the density current. In particular persistent billow generation, similar to that found in shear layers and associated with Kelvin–Helmholtz instabilities, is observed.

Custom-produced fluorescent particles are presented and their use as tracers for particle image velocimetry is evaluated. The fabrication procedure is explained and the main properties of the particles are described. The advantages of using fluorescent particles over nonfluorescent ones are discussed, in particular, for applications involving large facilities, as those used in hydraulic research. Images using the produced particles are also shown.

Laboratory experiments were conducted to study the formation of layers and interfaces in a fluid stratified with two scalars. Fluid with initially linear, diffusively stable temperature and salinity profiles was stirred using an arrangement of horizontally oscillating, vertical rods. Layers occurred when the density ratio, or the ratio of the contributions of temperature and salinity to the density gradient, was small, but they did not form in similar conditions of turbulence intensity and stratification strength when the density ratio was large. The difference in behavior is ascribed to differential diffusion, or the preferential transport of temperature, which occurred in all of the experiments. Eddy diffusivities were linearly proportional to ɛa/νN 2, where ɛa is an averaged rate of dissipation of turbulent kinetic energy. The mixing efficiency, computed as the ratio of potential energy change to work input to the system, increased with the density ratio. As previous researchers have found, the Phillips–Posmentier mechanism describes the final layered state but not the initial, evolving states of the system.

A finite element simulation of flow and heat transfer in the moderator cell of a cold-neutron source (CNS), in which liquid deuterium subject to internal heat generation is flowing, is reported. The numerical scheme consists of a stabilized equal-order method. A time-accurate approach is adopted to resolve the large-scale eddies of the flow, with a Smagorinsky's model for the subgrid-scale effects. The thermal coupling follows a staggered strategy, with SUPG-type upwinding. A specific wall-law is developed that accounts for the correct partition of the heat deposited at the wall by radiation between the liquid deuterium and the helium gas flowing at the outer side of the wall. The average flow and thermal structure are presented. The turbulent fluctuations are both illustrated in physical space and decomposed into spectral components. The wavenumber spectrum suggests that adequate resolution of the large-scale eddies has been attained with just 200,000 nodes, while a DNS analysis would have required at le...