Instability Analysis of Incompressible Open Cavity Flows

El problema del flujo sobre una cavidad abierta ha sido estudiado en profundidad en la literatura, tanto por el interés académico del problema como por sus aplicaciones prácticas en gran variedad de problemas ingenieriles, como puede ser el alojamiento del tren de aterrizaje de aeronaves, o el depósito de agua de aviones contraincendios. Desde hace muchos a˜nos se estudian los distintos tipos de inestabilidades asociadas a este problema: los modos bidimensionales en la capa de cortadura, y los modos tridimensionales en el torbellino de recirculación principal dentro de la cavidad. En esta tesis se presenta un estudio paramétrico completo del límite incompresible del problema, empleando la herramienta de estabilidad lineal conocida como BiGlobal. Esta aproximación permite contemplar la estabilidad global del flujo, y obtener tanto la forma como las características de los modos propios del problema físico, sean estables o inestables. El estudio realizado permite caracterizar con gran detalle todos los modos relevantes, así como la envolvente de estabilidad en el espacio paramétrico del problema incompresible (Mach nulo, variación de Reynolds, espesor de capa límite incidente, relación altura/profundidad de la cavidad, y longitud característica de la perturbación en la dirección transversal). A la luz de los resultados obtenidos se proponen una serie de relaciones entre los parámetros y características de los modos principales, como por ejemplo entre el Reynolds crítico de un modo, y la longitud característica del mismo. Los resultados numéricos se contrastan con una campaña experimental, siendo la principal conclusión de dicha comparación que los modos lineales están presentes en el flujo real saturado, pero que existen diferencias notables en frecuencia entre las predicciones teóricas y los experimentos. Para intentar determinar la naturaleza de dichas diferencias se realiza una simulación numérica directa tridimensional, y se utiliza un algoritmo de DMD (descomposición dinámica de modos) para describir el proceso de saturación. ABSTRACT The problem of the flow over an open cavity has been studied in depth in the literature, both for being an interesting academical problem and due to the multitude of industrial applications, like the landing gear of aircraft, or the water deposit of firefighter airplanes. The different types of instabilities appearing in this flow studied in the literature are two: the two-dimensional shear layer modes, and the three-dimensional modes that appear in the main recirculating vortex inside the cavity. In this thesis a parametric study in the incompressible limit of the problem is presented, using the linear stability analysis known as BiGlobal. This approximation allows to obtain the global stability behaviour of the flow, and to capture both the morphological features and the characteristics of the eigenmodes of the physical problem, whether they are stable or unstable. The study presented here characterizes with great detail all the relevant eigenmodes, as well as the hypersurface of instability on the parameter space of the incompressible problem (Mach equal to zero, and variation of the Reynolds number, the incoming boundary layer thickness, the length to depth aspect ratio of the cavity and the spanwise length of the perturbation). The results allow to construct parametric relations between the characteristics of the leading eigenmodes and the parameters of the problem, like for example the one existing between the critical Reynolds number and its characteristic length. The numerical results presented here are compared with those of an experimental campaign, with the main conclusion of said comparison being that the linear eigenmode are present in the real saturated flow, albeit with some significant differences in the frequencies of the experiments and those predicted by the theory. To try to determine the nature of those differences a three-dimensional direct numerical simulation, analyzed with Dynamic Mode Decomposition algorithm, was used to describe the process of saturation

On linear instability mechanisms in incompressible open cavity flow

A theoretical study of linear global instability of incompressible flow over a rectangular spanwise-periodic open cavity in an unconfined domain is presented. Comparisons with the limited number of results available in the literature are shown. Subsequently, the parameter space is scanned in a systematic manner, varying Reynolds number, incoming boundary-layer thickness and length-to-depth aspect ratio. This permits documenting the neutral curves and leading eigenmode characteristics of this flow. Correlations constructed using the results obtained collapse all available theoretical data on the three-dimensional instabilities

Energía y confort. La evolución histórica de la fachada en la arquitectura occidental

[EN] The envelope is considered to be the boundary between the outside and the inside of a building. The aim of this study is to analyze both the process that led the concept of the façade to evolve in Western architecture and the repercussions of such evolution, focusing on energy consumption and comfort. The entire evolution of the façade has been closely related to the evolution of materials and construction technologies. The comfort and energy characteristics of architecture have always been determined by the materials and construction technologies employed in façades. Architecture has improved in technical aspects, especially in terms of lighting and thermal comfort. Nevertheless, thermal comfort is usually linked to energy consumption, which is the parameter that has increased the most in this development, with the only exception being sustainable architecture.[ES] La envolvente se considera el límite entre el exterior y el interior de un edificio. El objetivo de este estudio es analizar el proceso que llevó a la evolución del concepto de fachada en la arquitectura occidental y las repercusiones de dicha evolución, centrándose en el consumo energético y el confort. Toda la evolución de la fachada ha estado estrechamente relacionada con la evolución de los materiales y las tecnologías de la construcción. El confort y las características energéticas de la arquitectura siempre han estado determinados por los materiales y tecnologías de construcción empleadas en las fachadas. La arquitectura ha mejorado en aspectos técnicos, especialmente en términos de iluminación y confort térmico. Sin embargo, el confort térmico suele estar ligado al consumo de energía, que es el parámetro que más ha aumentado en esta evolución, con la única excepción de la arquitectura sostenible.Sánchez-Ramos, I.; Raposo Grau, JF.; Meseguer-Garrido, F.; Mediavilla-Martín, D. (2022). Energy and comfort. The historical evolution of the façade in Western Architecture. VLC arquitectura. Research Journal. 9(2):179-200. https://doi.org/10.4995/vlc.2022.165421792009

Unsteady residual distribution schemes for transition prediction

In this work, the unsteady simulation of the Navier–Stokes equations is carried out by using a Residual Distribution Schemes (RDS) methodology. This algorithm has a compact stencil (cell-based computations) and uses a finite element like method to compute the residual over the cell. The RDS method has been successfully proven in steady Navier–Stokes computation but its application to fully unsteady configurations is still not closed, because some of the properties of the steady counterpart can be lost. Here, we proposed a numerical solution for unsteady problems that is fully compatible with the original approach. In order to check the method, we chose a very demanding test case, namely the numerical simulation of a Tollmien–Schlichting (TS) wave in a 2D boundary layer. The evolution of this numerical perturbation is accurately computed and checked against theoretical results

Generalization of the pedal concept in bidimensional spaces. Application to the limaçon of Pascal

The concept of a pedal curve is used in geometry as a generation method for a multitude of curves. The definition of a pedal curve is linked to the concept of minimal distance. However, an interesting distinction can be made for ℝ2. In this space, the pedal curve of another curve C is defined as the locus of the foot of the perpendicular from the pedal point P to the tangent to the curve. This allows the generalization of the definition of the pedal curve for any given angle that is not 90º. In this paper, we use the generalization of the pedal curve to describe a different method to generate a limaçon of Pascal, which can be seen as a singular case of the locus generation method and is not well described in the literature. Some additional properties that can be deduced from these definitions are also describedEl concepto de curva podal está extendido en la geometría como un método generativo para multitud de curvas. La definición de curva podal está ligada al concepto de mínima distancia. Sin embargo, es posible hacer una interesante distinción en el espacios ℝ2. En este caso, la curva podal de otra curva C se define como el lugar geométrico de los pies de las perpendiculares desde un punto P a las tangentes a la curva. Esto permite generalizar la definición de curva podal a cualquier ángulo que no sea 90º. En este artículo utilizamos la generalización de curva podal para describir un método diferente de generación de la Limaçon de Pascal, que puede relacionarse como un caso particular del método de generación por lugares geométricos y que no se encuentra bien descrito en la literatura. También se describen algunas propiedades que pueden deducirse de estas definicione

Generalization of the pedal concept in bidimensional spaces. Application to the limaçon of Pascal = Generalización del concepto de curva podal en espacios bidimensionales. Aplicación a la Limaçon de Pascal

The concept of a pedal curve is used in geometry as a generation method for a multitude of curves. The definition of a pedal curve is linked to the concept of minimal distance. However, an interesting distinction can be made for ?2. In this space, the pedal curve of another curve C is defined as the locus of the foot of the perpendicular from the pedal point P to the tangent to the curve. This allows the generalization of the definition of the pedal curve for any given angle that is not 90º. In this paper, we use the generalization of the pedal curve to describe a different method to generate a limaçon of Pascal, which can be seen as a singular case of the locus generation method and is not well described in the literature. Some additional properties that can be deduced from these definitions are also described. ----------RESUMEN---------- El concepto de curva podal está extendido en la geometría como un método generativo para multitud de curvas. La definición de curva podal está ligada al concepto de mínima distancia. Sin embargo, es posible hacer una interesante distinción en el espacios ℝ2. En este caso, la curva podal de otra curva C se define como el lugar geométrico de los pies de las perpendiculares desde un punto P a las tangentes a la curva. Esto permite generalizar la definición de curva podal a cualquier ángulo que no sea 90º. En este artículo utilizamos la generalización de curva podal para describir un método diferente de generación de la Limaçon de Pascal, que puede relacionarse como un caso particular del método de generación por lugares geométricos y que no se encuentra bien descrito en la literatura. También se describen algunas propiedades que pueden deducirse de estas definiciones

Wind tunnel testing on the new control tower of the Fujairah International Airport

The design of the new control tower of Fujairah International Airport is characterized by the geometry of the tower, inspired by the profile of a falcon and the curved surfaces of the roof of the auxiliary building. It is not possible to assimilate this peculiar geometry to the prototypical ones found in the application codes for wind action determination. In this article the process to carry out a wind tunnel testing campaign on a scale model of this building. The testing model has been constructed combining different techniques of carpentry, modelling, CNC milling and stereo-lithography (3D printing) and it was instrumented with 588 pressure taps. The effect on the aerodynamic loads of the buildings located around the tower has been studied. The results show that the distribution of pressures on the control tower and the auxiliary building are significantly modified depending on the configuration of the surrounding buildings

Transverse motions of a single sphere in hanging or swing configurations under a longitudinal flow

As a result of the reporting of casual observations of the oscillation or rotation of the beacons in transmission line guard cables, some attention has been paid to the stability of the guard cables with beacons. The relatively more frequent observation of these motions has been explained in recent papers dealing with the elastic part of the problem as a consequence of the increasing number of resonant frequencies (one for each additional beacon) that can be excited by appropriate aerodynamic loads. But a model that could explain the aerodynamic forces that can give rise to this motion is still lacking. In this paper we consider the transverse motions of a single sphere in two simplified configurations, (1) hanging (tethered at one point), and (2) swing (tethered at two points) under a longitudinal flow, performing small amplitude swinging oscillations or circular-orbit autorotation about an axis parallel to the main flow direction. The dynamic model here presented is based on the motion equations, which also include a model for the aerodynamic lift and drag forces on the sphere in transverse motion, which considers the effect of changes of flow around the sphere due to the cable interference. These forces are contained in the symmetry plane of the flow relative to the sphere, and, when projected on the lateral direction, give rise to a lateral force, which can explain the existence of the azimuthal motion even at a large reduced velocity, outside the vortex induced vibration (VIV) range The conditions for stable small oscillation motion and circular-orbit autorotation of a sphere in a swing configuration are given. The results for the aerodynamic loads in transverse motion have also been applied to the case of a circular-orbit autorotation of a hanging sphere (spherical pendulum) under a vertical flow. The angular rotation speed and the orbit radius (or cable angle) have been determined as a function of aerodynamic coefficients and configuration parameters

Characterization of the wind flow on the flight deck of a frigate

Helicopter operations in frigate-type boats can be critical depending on the sea and wind conditions. Dueto the non-steadiness and wide variations of the mean velocity, the flight envelope is limited, being theapproach to the flight deck one of the most complex and risky operations a helicopter can perform. Usually,the flight deck in the frigates is located in the stern. As a consequence, the wind flow in the surroundingsof the flight deck is highly conditioned by the wake generated by the freeboard of the boat. This wake ishighly turbulent and full of strong vortexes. These vortexes depend on the geometry of the boat upstreamthe flight deck. The correct characterization of this complex flow is related to the safety of the operationof the aircraft and allows to set the limits in which the deck can be operative or be certified. In this work,some partial results of an extensive wind tunnel test campaign are presented. In this campaign, a model ofthe frigate has been tested. The aim is to characterize the flow in the surroundings of the flight deck of thefrigate. For that, visualization tests with wool tufts and smoke, hot wire anemometry and particle imagevelocimetry (PIV) have been performed. All the tests have been done in the experimental aerodynamicsfacilities of the Instituto Universitario “Ignacio Da Riva”, belonging to the Universidad Politécnica deMadrid. Based on the information obtained in the tests, small modifications in the freeboard are suggested,in order to optimize the flow in the flight deck, which can make the approach operation easier for the pilots

Metatranscriptomic analysis of extremely halophilic viral communities

Hypersaline environments harbour the highest number of viruses reported for aquatic environments. In crystallizer ponds from solar salterns, haloviruses coexist with extremely halophilic Archaea and Bacteria and present a high diversity although little is known about their activity. In this work, we analyzed the viral expression in one crystallizer using a metatranscriptomic approach in which clones from a metaviromic library were immobilized in a microarray and used as probes against total mRNA extracted from the hypersaline community. This approach has two advantages: (i) it overcomes the fact that there is no straightforward, unambiguous way to extract viral mRNA from bulk mRNAs and (ii) it makes the sequencing of all mRNAs unnecessary. Transcriptomic data indicated that the halovirus assemblage was highly active at the time of sampling and the viral groups with the highest expression levels were those related to high GC content haloarchaea and Salinibacter representatives, which are minor components in the environment. Moreover, the changes in the viral expression pattern and in the numbers of free viral particles were analyzed after submitting the samples to two stress conditions: ultraviolet-radiation and dilution. Results showed that Archaea were more sensitive than Bacteria to these stress conditions. The overexpression in the predicted archaeal virus fraction raised and the total numbers of free viruses increased. Furthermore, we identified some very closely related viral clones, displaying single-nucleotide polymorphisms, which were expressed only under certain conditions. These clones could be part of very closely related virus genomes for which we propose the term 'ecoviriotypes'. © 2011 International Society for Microbial Ecology. All rights reserved.This work was supported by projects CGL2006-12714-CO2-01 and -02, and AYA2008-04013 of the Spanish Ministry of Science and Innovation (MICINN), which include funding from the European Union (‘FEDER’) and ACOM09/155 from the Generalitat Valenciana.Peer Reviewe