423 research outputs found
Wingtip vortex in a NACA0012 airfoil and its active control
ContribuciĂłn mediante sesiĂłn pĂłsterWe conduct experiments in a towing-tank to analyse the flow patterns of wingtip vortices in a NACA 0012 airfoil. In this experimental research, we provide PIV measurements and flow visualisations. Without active control, several parameters are given experimentally as function of the Reynolds number, so we compare these data with the theoretical models of Batchelor, and Moore and Saffman together with DNS. Secondly, we analyse the effect of a continuous injection in the spanwise direction. The continuous jet has a strong influence on the wing-tip vortex formation. We explore this effect at low chord based Reynolds number ranging from 7000 up to 20000. We change the aspect ratio of the injection, R, defined as the ratio of the velocities between the jet (Uj) and free-stream (U). For R=1, we find that the jet strongly affects the wingtip vortex formation with a sudden decrement of the axial vorticity and the azimuthal velocity. This technique is a challenge and a promising tool to reduce the intensity of the vortex core.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Effect of the axial jet on the optimal response in Batchelor vortex
En este pĂłster se estudia la respuesta Ăłptima del torbellino de Batchelor para distintos nĂșmeros de onda. Se demuestra que incluso teniendo la velocidad axial, un torbellino es capaz de tener grandes amplificaciones de energĂa.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Influence of Reynolds number on theoretical models for trailing vortices
We conduct direct numerical simulations for a NACA0012 airfoil at Reynolds numbers (Re) ranging from 300 to 7000 to determine the wake behavior behind this wing profile. We characterize the structure of the wing-tip vortex, finding a reasonable agreement with experimental results at Re=7000. In addition, we model the trailing vortex theoretically, thus obtaining the parameters for Batchelorâs and Moore and Saffmanâs models. We compare the results of the best fitting for the axial vorticity and the azimuthal velocity, finding only small discrepancies. The main contribution of this research work is to study the evolution of these theoretical parameters as function of the Reynolds number. We observe that the wake becomes unstable at Re â1200, in agreement with previous results. These instabilities in the wake behind the wing produce a change in the trend of theoretical parameters (keywords: vortex dynamics, trailing vortices, theoretical models).Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Parabolic trough collectors. Fundamentals of heat transfer applied to solar thermal energy.
Solar thermal energy has undergone major development in recent years. The most
widely used technologies are central receiver solar towers and parabolic trough collectors (PTC)[1]. The latter technology has great advantages due to its higher optical
and thermal efficiency, but, despite being a well-proven technique, it presents certain
problems inherent to the manufacturing and durability of some critical elements in
the system. They are generally composed of an absorber tube surrounded by a glass
cover and in the intermediate space, a vacuum is created to minimize thermal losses
by convection[2]. The absorber tube is located at the focal line of a parabolic mirror
that concentrates sunâs rays. To predict the thermal behavior of this type of system,
ray-tracing techniques are used to determine the thermal load and accurate correlations are also needed to calculate the convective heat transfer. Also, the original design
shows some problems such as the selective coating applied on the absorber surface,
whose thermal performance decays with time. Besides, the metal-glass welding are
also a significant weak spot, which due to the thermal expansion can cause the partial
or total loss of the vacuum in the aforementioned annulus. In this work we present the
results of the modeling of this type of systems in different working configurations, as
well as a new design proposal to improve the thermal transfer in this type of systems.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Structural plasticity in I-Ag7 links autoreactivity to hybrid insulin peptides in type I diabetes
We recently provided evidence for promiscuous recognition of several different hybrid insulin peptides (HIPs) by the highly diabetogenic, I-Ag7-restricted 4.1-T cell receptor (TCR). To understand the structural determinants of this phenomenon, we solved the structure of an agonistic HIP/I-Ag7 complex, both in isolation as well as bound to the 4.1-TCR. We find that HIP promiscuity of the 4.1-TCR is dictated, on the one hand, by an amino acid sequence pattern that ensures I-Ag7 binding and, on the other hand, by the presence of three acidic residues at positions P5, P7 and P8 that favor an optimal engagement by the 4.1-TCR's complementary determining regions. Surprisingly, comparison of the TCR-bound and unbound HIP/I-Ag7 structures reveals that 4.1-TCR binding triggers several novel and unique structural motions in both the I-Ag7 molecule and the peptide that are essential for docking. This observation indicates that the type 1 diabetes-associated I-Ag7 molecule is structurally malleable and that this plasticity allows the recognition of multiple peptides by individual TCRs that would otherwise be unable to do so.Copyright © 2022 Erausquin, Serra, Parras, Santamaria and López-Sagaseta
FeAl and NbAl3 intermetallic- HVOF coatings: structure and properties
Transition metal aluminides in their coating form are currently being explored in terms of resistance to oxidation and mechanical behavior. This interest in transition metal aluminides is mainly due to the fact that their high Al content makes them attractive for high-temperature applications. This is also a reason to study their resistance to wear; they may be suitable for use in applications that produce a lot of wear in aggressive environments, thus replacing established coating materials. In this study, the microstructure, microhardness, and wear and oxidation performance of FeAl and NbAl3 coatings produced by highvelocity oxy-fuel spraying are evaluated with two main aims: (i) to compare these two coating systemsÂża commonly studied aluminide (FeAl) and, NbAl3, an aluminide whose deposition by thermal spraying has not been attempted to dateÂżand (ii) to analyze the relationship between their microstructure, composition and properties, and so clarify their wear and oxidation mechanisms. In the present study, the higher hardness of niobium aluminide coatings did not correlate with a higher wear resistance and, finally, although pesting phenomena (disintegration in oxidizing environments) were already known of in bulk niobium aluminides, here their behavior in the coating form is examined. It was shown that such accelerated oxidation was inevitable with respect to the better resistance of FeAl, but further improvements are foreseen by addition of alloying elements in that alloy
Feasibility of using low pressure cold gas spray for the spraying of thick ceramic hydroxyapatite coatings
This article deals with the production of thick ceramic hydroxyapatite coatings obtained by Low Pressure Cold Gas Spray (LPCGS) system. Several factors such as powder microstructure, surface roughness and cold gas spray system are here discussed in the buildâup process. The use of nanocrystalline powder composed by fine agglomerates and needleâlike shape microstructure allows the realignment and compaction of individual crystallites to form thick deposits. In addition, the activation of the substrate surface results convenient for the first impinging particles anchored properly. Then, layer by layer, particles can remain attached leading to coating buildâup. Additionally, the use of low shock pressure as well as constant feeding system provided by LPCGS system lead to homogeneous coatings in comparison with High Pressure Cold Gas Spray (HPCGS) system. The successful coating buildâup has been achieved not only by the use of an agglomerated feedstock powder, but also by previous surface treatment and the use of the low pressure system. The obtaining of HA components by LPCGS is promising within biomedical field. An improvement of component strength is also suggested by means of thermomechanical analysis of the powder. The performance of a post heatâtreatment leads to an increase in HA strength, as well as crystal size
The effect of hot treatment on composition and microstructure of HVOF iron aluminide coatings in Na2SO4 molten salts
The paper deals with the hot corrosion performance of FeAl base intermetallic HVOF coatings in molten Na2SO4 at 850 C in an isothermal process over the span of 45 h under static conditions. The test was validated with electron microscopy and compositional analyses in the cross-section area, as well as x-ray diffraction techniques. All the coatings were characterized by Al-depleted regions, intersplat oxidation and different stoichiometric ratios of iron aluminides. The results were discussed in relation to the formation of oxide scales on the surface after exposition to corrosive media, as well as heterogeneity and defects of the sprayed coatings. The Fe40Al (at.%) powder showed quite uniform phase distribution after spraying and preserved its integrity after corrosion test; the FeCr25% ? FeAl-TiAl-Al2O3 (wt.%) and Fe46Al-6.55Si (at.%) powders exhibited interface oxidation, with localized corrosion attacks proceeding through particle boundaries and microcrack networks with no evidence of Na and S penetration. FexAly alloys are susceptible to accelerated damage and decohesion of the coating, whereas the formation of sulfides is observed at certain points
Deciphering the Potential Coding of Human Cytomegalovirus: New Predicted Transmembrane Proteome
CMV is a major cause of morbidity and mortality in immunocompromised individuals that will benefit from the availability of a vaccine. Despite the efforts made during the last decade, no CMV vaccine is available. An ideal CMV vaccine should elicit a broad immune response against multiple viral antigens including proteins involved in virus-cell interaction and entry. However, the therapeutic use of neutralizing antibodies targeting glycoproteins involved in viral entry achieved only partial protection against infection. In this scenario, a better understanding of the CMV prote-ome potentially involved in viral entry may provide novel candidates to include in new potential vaccine design. In this study, we aimed to explore the CMV genome to identify proteins with puta-tive transmembrane domains to identify new potential viral envelope proteins. We have performed in silico analysis using the genome sequences of nine different CMV strains to predict the trans-membrane domains of the encoded proteins. We have identified 77 proteins with transmembrane domains, 39 of which were present in all the strains and were highly conserved. Among the core proteins, 17 of them such as UL10, UL139 or US33A have no ascribed function and may be good candidates for further mechanistic studies
Influence of Cold Gas Spray process conditions on the microstructure of Fe-based amorphous coatings
Fe-based amorphous metallic coatings were prepared by Cold Gas Spray process. Through this study, the effects of the process conditions such as spraying distance, gas pressure and temperature on the microstructure of as-sprayed coatings are evaluated. Microstructural studies show that the coatings can present a densely layered structure with porosity below 0.5% and thickness around 800 ÎŒm depending on the process conditions. Precipitation of nanocrystals in as-sprayed coatings is observed and present results show its dependence on the thermal and kinetic energy implicated in the process. In general, when gas temperature and pressure decreased, in the studied range, coatings displayed a dense and amorphous structure
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