Nonlinear evolution of harmonically forced perturbations on a wingtip vortex

Wingtip vortices are created by flying airplanes due to lift generation. The vortex interaction with the trailing aircraft has sparked researchers’ interest to develop an efficient technique to destroy these vortices. Different models have been used to describe the vortex dynamics and they all show that, under real flight conditions, the most unstable modes produce a very weak amplification. Another linear instability mechanism that can produce high energy gains in short times is due to the non-normality of the system. Recently, it has been shown that these non-normal perturbations also produce this energy growth when they are excited with harmonic forcing functions. In this study, we analyze numerically the nonlinear evolution of a spatially, pointwise and temporally forced perturbation, generated by a synthetic jet at a given radial distance from the vortex core. This type of perturbation is able to produce high energy gains in the perturbed base flow (10^3), and is also a suitable candidate for use in engineering applications. The flow field is solved for using fully nonlinear three-dimensional direct numerical simulation with a spectral multidomain penalty method model. Our novel results show that the nonlinear effects are able to produce locally small bursts of instability that reduce the intensity of the primary vortex.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Effect of the axial jet on the optimal response in Batchelor vortex

En este póster se estudia la respuesta óptima del torbellino de Batchelor para distintos números de onda. Se demuestra que incluso teniendo la velocidad axial, un torbellino es capaz de tener grandes amplificaciones de energía.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Wingtip vortex in a NACA0012 airfoil and its active control

Contribución mediante sesión pósterWe 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 Málaga. Campus de Excelencia Internacional Andalucía Tech

On the effect of low blowing ratio continuous jets on wingtip vortex characteristics

Vortices are an unavoidable effect of flight, which appear behind the wing with a bounded length. The strength of these vortices, which are extremely stable, is due to the lift force [1]. That is the reason why this phenomenon is especially relevant during take-off and landing operations. In these situations, when aircraft are departing from or arriving to the airport runways, the following aircraft might feel two counter-rotating vortices which remain long time under normal environmental conditions. Unfortunately, this huge rotation of airflow patterns always destabilizes the following aircraft. Consequently, trailing vortices have a mighty influence on the air traffic control of airport runways, and they have justified the research interest in this topic since the 1960's [2]. However, aeronautical engineers are still searching for different technological strategies to breakdown these wingtip vortices.Short-Term Postdoctoral Stay of Talent Attraction Plan of Andalucía TECH ICE. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

New Architectures based on Isotactic Polypropylene: Synthesis and Molecular Characterization, Competition between Polymorphs (monoclinic / orthorhombic / mesomorphic / trigonal), and Properties Evaluation

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de lectura: 23-11-2015El polipropileno isotáctico se encuentra presente en una enorme variedad de aplicaciones, que lo sitúan en la segunda posición de los polímeros con mayor demanda mundial, los denominados “commodities”. Las necesidades del mercado, la expansión de su uso así como nuevas políticas, medioambientales entre otras, están detrás de los numerosos esfuerzos que se llevan a cabo a diario para mejorar las arquitecturas existentes y diseñar otras nuevas basadas en ellas, con objeto de optimizar y ampliar su espectro de propiedades. El presente trabajo de investigación tiene, por tanto, el propósito último de incidir en las posibilidades que ofrecen los copolímeros y terpolímeros de propileno con alfa-olefinas de longitudes intermedias como comonómeros (1-penteno, 1-hexeno y 1-hepteno), motivado por el hallazgo en 2005 de una nueva estructura cristalina (celdilla trigonal) en copolímeros de propileno con 1-penteno y 1-hexeno a elevados contenidos. Para ello, se han sintetizado diferentes familias de copolímeros de propileno-co-1-penteno, propileno-co-1-hexeno y propileno-co-1-hepteno en intervalos amplios de composición de los comonómeros, así como terpolímeros de propileno-co-1-penteno-co-1-hexeno y propileno-co-1-penteno-co-1-hepteno, en los que, además, se varió el ratio entre comonómeros a una composición global dada. Se han preparado también los homopolímeros correspondientes, es decir, el polipropileno isotáctico, el poli(1-penteno), el poli(1-hexeno) y el poli(1-hepteno). Los numerosos materiales obtenidos presentan pesos moleculares suficientemente elevados así como una alta isotacticidad, características que garantizan unas buenas prestaciones mecánicas, como se ha comprobado. Un entendimiento adecuado de las estructuras cristalinas que pueden generarse y, consecuentemente, de las propiedades finales que pueden manifestar estos materiales, ha requerido una minuciosa evaluación de su microestructura. De ella se ha deducido que la inserción de los monómeros durante la polimerización se produce al azar. A continuación, se ha realizado un estudio pormenorizado sobre las diferentes estructuras cristalinas existentes, la competencia entre los diversos polimorfos y sus transiciones de fase, para cada una de las familias sintetizadas, en función de la composición, la velocidad de cristalización y el ratio entre comonómeros. Se ha prestado especial atención a las condiciones para obtener la mesofase y la nueva modificación trigonal. Finalmente, se ha procedido al estudio de algunas propiedades que se han considerado de interés para futuras posibles aplicaciones, haciendo incidencia en su comportamiento mecánico, su caracterización óptica y sus propiedades de transporte. Además, se ha realizado un estudio pionero sobre la estabilidad térmica de los copolímeros de propileno con 1-penteno y 1-hexeno. En general, las propiedades han resultado ser muy sensibles tanto a la cristalinidad total como a la naturaleza de las diversas fases presentes, lo que ha permitido obtener materiales polímeros en un extenso espectro de propiedades, que se pueden modular a voluntad en un amplio intervaloIsotactic polypropylene can be found in an enormous variety of applications, and, consequently, its demand is extraordinary high between those polymers denominated as “commodities”. Requirements of markets joined to expansion of its uses and new environmental policies, among others factors, are underneath the numerous efforts that are being carried out in order to enhance the existing architectures and to design new ones, aiming optimization and expansion of its properties range. The present research work has the final purpose of exploring the possibilities offered by copolymers and terpolymers based on propylene and alpha-olefins of different lengths as comonomers (1-pentene, 1-hexene, and 1-heptene), primarily motivated by the discovery in 2005 of a new crystalline structure (trigonal lattice) in propylene copolymers at high contents of 1-pentene or 1-hexene. For that, different families of propylene-co-1-pentene, propylene-co-1-hexene and propylene-co-1- heptene copolymers have been synthesized in a wide range of comonomer compositions, as well as propylene-co-1-pentene-co-1-hexene and propylene-co-1- pentene-co-1-heptene terpolymers, where the ratio between comonomers has been additionally varied at a given global composition. Moreover, the corresponding homopolymers have been also prepared, namely isotactic polypropylene, poly(1- pentene), poly(1-hexene) and poly(1-heptene). All these numerous materials prepared present sufficiently high molecular weights and high isotacticity, both features ensuring good mechanical performance, as observed. The adequate understanding of the different crystalline structures that can be developed and, consequently, of the final properties exhibited by these materials, required a detailed and thorough evaluation of the microstructure. From that, a random inclusion of the monomers during polymerization has been deduced. In addition, the different existing crystalline lattices, the competence between the various polymorphs and their phase transitions have been studied in detail for the different materials synthesized, as function of composition, crystallization rate and comonomers ratio. Special attention has been paid to the conditions for obtaining the mesophase and the new trigonal modification. Finally, some properties of interest for possible future applications have been studied, especially the mechanical behavior, optical response, and transport properties. In addition, a pioneer study on the thermal stability of propylene copolymers with 1-pentene and 1-hexene has been performed. In general, properties have turned out very sensitive both to the global crystallinity and to the nature of the phases involved, so that polymer materials covering a broad spectra of properties have been obtained and their ultimate performance can be widely tailore

On the optimaL response of q-vortex

Wingtip vortices represent a hazard for the stability of the following airplane in airport highways. These flows have been usually modeled as swirling jets/wakes, which are known to be highly unstable and susceptible to breakdown at high Reynolds numbers for certain flow conditions, but different to the ones present in real flying airplanes. A very recent study based on Direct Numerical Simulations (DNS) shows that a large variety of helical responses can be excited and amplified when a harmonic inlet forcing is imposed. In this work, the optimal response of q-vortex (both axial vorticity and axial velocity can be modeled by a Gaussian profile) is studied by considering the time-harmonically forced problem with a certain frequency ω. We first reproduce Guo and Sun’s results for the Lamb-Oseen vortex (no axial flow) to validate our numerical code. In the axisymmetric case m = 0, the system response is the largest when the input frequency is null. The axial flow has a weak influence in the response for any axial velocity intensity. We also consider helical perturbations |m| = 1. These perturbations are excited through a resonance mechanism at moderate and large wavelengths as it is shown in Figure 1. In addition, Figure 2 shows that the frequency at which the optimal gain is obtained is not a continuous function of the axial wavenumber k. At smaller wavelengths, large response is excited by steady forcing. Regarding the axial flow, the unstable response is the largest when the axial velocity intensity, 1/q, is near to zero. For perturbations with higher azimuthal wavenumbers |m| > 1, the magnitudes of the response are smaller than those for helical modes. In order to establish an alternative validation, DNS has been carried out by using a pseudospectral Fourier formulation finding a very good agreement.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

On the Political Determinants of Intergovernmental Grants in Decentralized Countries: The Case of Spain

This paper studies the effect of political variables on the gains obtained by Spanish regions in periodical bargaining of the intergovernmental financing agreements and on the regional distribution of discretional earmarked grants over the period 1987-2008. First, we find that the relationship between gains in transferred revenues and on regional public debt stocks depends on the period and the specific issues discussed in the corresponding negotiation, aside from political affinity. Second, we show that the most discretional program of earmarked grants is strongly driven by electoral strategy. National incumbents tend to allocate intergovernmental transfers where there are competitive regional elections. We also show that earmarked grants are allocated in those regions where the incumbent performs better in national elections and, especially, in those where there are more seats to be won. Hence we prove that both strategies are complementary rather than exclusive.España. Ministerio de Ciencia e Innovación ECO2010-1555

PIV measurements of the effect of pulsed blowing jet on a NACA0012 wing model

Wingtip vortices are present in taking off, and landing operations and their presence in airport runways must be reduced. To that end, several strategies have been considered in the last decades, being the active control one possible technical solution. To compute the effectiveness of active control that corresponds to pulsed low-blowing-ratio transverse jet for the reduction of the wingtip vortex strength, we carry out 2D-PIV measurements in a towing tank for chord-based Reynolds numbers 15000 and 20000. We consider two cases: (i) no active control Rjet=0 and (ii) pulsating radial jet of blowing-ratio Rjet smaller than 1.7 (or momentum coefficient lower than 0.12) and different Strouhal numbers ranging from 0.27 to 0.94. Our observations show that the best reduction of wingtip vortex strength takes place at the lowest Strouhal number tested. We use the maximum azimuthal velocity and vorticity together with the circulation to quantify this decrease in the vortex strength. Besides, we define the spatial evolution of a disturbance parameter which allow us to detect again the optimal frequency that leads to vortex destruction.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Simulation of working procedures in a distribution centre

This simulation study has been developed to assess a set of realistic proposals of a new distribution centre to a pharmaceutical company, with a focus on the sorting operation. Different sorting strategies, establishing dynamic assignment of the lanes to destinations and lanes to operators are proposed. Also different packing procedures have been presented according to the operator way of working. New qualitative criterions have been defined to evaluate the strategies. The results show some interesting non-linear behaviour in the sorting operation, and give the number of required operators, length of the lanes, and working procedures to be used in this application. The simulation experiments show that the improvement in the overall productivity by choosing a specific sorting strategy can be significant. The study has helped the management of the involved company to make a decision about the supplier and actually, the suggested proposals are being implemented in practice

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 Batchelor’s and Moore and Saffman’s 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 ≈1200, 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 Málaga. Campus de Excelencia Internacional Andalucía Tech