A non-linear observer for unsteady three-dimensional flows

A method is proposed to estimate the velocity field of an unsteady flow using a limited number of flow measurements. The method is based on a non-linear low-dimensional model of the flow and on expanding the velocity field in terms of empirical basis functions. The main idea is to impose that the coefficients of the modal expansion of the velocity field give the best approximation to the available measurements and that at the same time they satisfy as close as possible the non-linear low-order model. The practical use may range from feedback flow control to monitoring of the flow in non-accessible regions. The proposed technique is applied to the flow around a confined square cylinder, both in two- and three-dimensional laminar flow regimes. Comparisons are provided. with existing linear and non-linear estimation techniques

Mixing sensitivity to the inclination of the lateral walls in a T-mixer

One of the simplest geometries for micro-mixers has a T-shape, i.e., the two inlets join perpendicularly the mixing channel. The cross-sections of the channels are usually square/rectangular, as straight walls facilitate experimental and modeling analysis. On the contrary, this work investigates through Computational Fluid Dynamics the effect of a cross-section with lateral walls inclined of an angle α as such an inclination may stem from different microfabrication techniques. Considering water as operating fluid, the same mixing performance as square/rectangular cross-sections is obtained for inclinations α≤3°; this indicates the maximum admissible error on the perpendicularity of the walls in the manufacturing process. Above this value, the presence of inclined walls delays the onset of the engulfment regime at higher Reynolds numbers, and for α≥23°the mixing is hampered dramatically, as the flow is unable to break the mirror symmetry and enter in the engulfment regime. At low Reynolds numbers, the mixing is moderately improved for α≥10°, because the vortex regime presents a lower degree of symmetry than that of T-mixers with straight walls

Alimentação de duas espécies do gênero Pseudoplatystoma do Rio Negro, Pantanal da Nhecolândia, MS, Brasil.

Este trabalho investigou a dieta e reprodução de duas espécies de peixes Siluriformes migradores do rio Negro, Pantanal da Nhecolândia, sob a influência do pulso de inundação. As amostras foram realizadas com o uso de redes de espera e tarrafas com diversas malhagens. De cada exemplar capturado foram obtidas as seguintes informações: comprimento total, comprimento padrão, peso total, grau de repleção e peso estomacal. Para estudo de sobreposição alimentar foi utilizado o índice de Morisita-Horn e para o estudo da dieta o Índice Alimentar. Foram capturados 225 exemplares da espécie Pseudoplatystoma corruscans (Pintado) e 85 da espécie Pseudoplatystoma reticulatum (Cachara). Destes, foram obtidos 58 estômagos com algum conteúdo. Ambas as espécies intensificaram a tomada de alimento após o período de inundação e apresentaram consumo diferenciado de recursos alimentares, com sobreposições alimentares quase inexistentes. O Índice Alimentar demonstrou uma diferenciação bastante clara nas dietas destes dois peixes piscívoros, demonstrando através de suas presas que ambas convivem explorando os recursos por meio de comportamentos distintos. This study investigated the diet and reproduction of two species of Siluriforms fish, migrating from Negro river, Pantanal of Nhecolandia, under the influence of the inundation pulse. The samples were obtained using gill net and casting seine with different screen sizes. The following informations were obtained form each specimen: total and standard length, total weight, gut fullness and stomachic weight. The Morisita-Horn index was used to study the food overlap and the food index for diet. A total of 225 specimens of Pseudoplatystoma corruscans (Pintado) and 85 of Pseudoplatystoma reticulatum (Cachara) species were captured. From these samples, 58 stomachs had some content. Both species intensified the taking of food after the inundation period and presented differentiated consumption of food resources, with very low frequency of food overlap. The food index demonstrated a great differentiation in the diets of these two predators species, showing by their preys that both live exploiting the resources by distinct behaviours

Unsteady flow regimes in arrow-shaped micro-mixers with different tilting angles

Two arrow-shaped micro-mixers, obtained from the classical T-shaped geometry by tilting downward the inlet channels, are considered herein. The two configurations, having different tilting angle values, have been chosen since they show significantly different flow topologies and mixing performances at low Reynolds numbers. In the present paper, we use both experimental flow visualizations and direct numerical simulations to shed light on the mixing behavior of the two configurations for larger Reynolds numbers, for which the mixers present unsteady periodic flows, although in laminar flow conditions. The tilting angle influences the flow dynamics also in the unsteady regimes and has a significant impact on mixing. The configuration characterized by the lower tilting angle, i.e., α = 10°, ensures a better global mixing performance than the one with the larger angle, i.e., α = 20°

Application of the Cloude-Pottier decomposition to weather radar signatures

In this paper we apply the Cloude-Pottier decomposition to Weather Radar Signatures. First, we present the results of a simulation carried out at the Chemnitz University of Technology and give the expected H-α values for different rain intensities. A comparison with standard radarmeteorological variables is also given. Then, first ever images of Entropy and Anisotropy are presented for clouds and precipitation. Experimental Data are from the POLDIRAD Weather Facility in Oberpfaffenhofen, Germany

Analysis of Coal Combustion in Oxy-fuel Conditions through Pulsed Feeding Experiments in an Entrained Flow Reactor

Coal combustion is investigated in both air and oxy-fuel conditions in a pilot-scale entrained flow reactor able to provide high temperatures, heating rates and residence times. Measurements are carried out with different levels of complexity and are aimed at: assessing the thermal field inside the reactor; evaluating conversions of devolatilization or char combustion tests; identifying phenomena such as volatiles ignition and measuring the ignition delay time. Computational Fluid Dynamics was also used in order to provide a better understanding of the experimental evidences. Among the results, the ignition delay time was found to be larger in oxy-fuel conditions than in air, mainly because of the larger specific heat of the oxy-fuel environment. The proposed investigation may help the qualification of advanced experimental apparatus as entrained flow reactors, with the purpose to make them suitable for heterogeneous kinetics studies in oxy-fuel conditions

Effect of stratification on the mixing and reaction yield in a T-shaped micro-mixer

The effect of a small density difference, i.e., lower than 12%, between the two miscible liquid streams fed to a T-shaped junction is investigated experimentally and through numerical simulations. Micron-resolution particle image velocimetry (micro-PIV) experiments provided detailed support to the numerical analysis of how stratification influences flow features in different flow regimes. From dimensional analysis, we find that gravitational and inertial fluxes balance each other at a distance L=d/Ri from the confluence along the mixing channel, where d is the hydraulic diameter and Ri is the Richardson number. In general, at distances |y|≪L, the influence of gravity can be neglected, while at |y|≫L the two fluids are fully segregated; in particular, at the confluence, the flow field is the same as the one that we obtain assuming that the two inlet fluids are identical. Thus, in the segregated regime, the contact region separating the two fluids of the inlet streams remains vertical at distances |y|≪L along the mixing channel while it becomes progressively horizontal at |y|≈L. In the vortex regime as well, near the confluence the flow field presents a mirror symmetry, with a very small resulting degree of mixing; however, as we move down the mixing channel, when |y|>L, gravity becomes relevant, leading to a symmetry breaking that promotes convection and enhances mixing. When we further increase the Reynolds number, in the engulfment regime, the degree of mixing becomes much larger due to the mixing induced by the flow instability at the confluence and thus the successive stratification appears to have a small effect on the flow topology, with a degree of mixing that continues to grow very slowly in the mixing channel, similar to what happens in the case of identical inlet fluids. As expected, the onsets of the vortex and engulfment regimes occur at values of the Reynolds number Re that hardly depend on the density difference between the two inlet fluids, provided that Re is defined in terms of the fluid properties of a homogeneous fluid mixture. Finally, the reaction yield along the mixing channel is computed both from numerical and experimental data. In agreement with theoretical predictions, we found that the reaction yield depends on the Damköhler number and the kinetic constant, while it is independent of the density ratio, at least within the range of the investigated conditions

An Overview of Flow Features and Mixing in Micro T and Arrow Mixers

An overview of the mixing performances of micro T mixers operating with a single fluid is presented. The focus is on the relationship between the flow features and mixing. Indeed, T mixers are characterized by a variety of regimes for increasing Reynolds numbers; they are briefly described, in particular in terms of the three-dimensional vorticity field, which can explain the different mixing performances. The effects of changes in the aspect ratio of the channels are also reviewed. The role of instability and sensitivity analyses in highlighting the mechanisms of the onsets of the different regimes is then described. These analyses also suggest possible geometrical modifications to promote mixing. We focus on that consisting of the downward tilting of the inlet channels (arrow mixers). Arrow mixers are interesting because the onset of the engulfment regime is anticipated at lower Reynolds numbers. Hence, the mixing performances of arrow mixers with varying Reynolds number are described

Genome Sequence Announcement of Lactobacillus vaginalis S-26419, Isolated from a Healthy Woman

The Lactobacillus vaginalis LMG S-26419 strain, also named CBA-L88 (BV2), was isolated at the AAT-Advanced Analytical Technologies laboratories from a vaginal swab obtained from a healthy woman. The total genome size is 1,806,242\u2009bp with a G+C content of 40.6%