Aerodynamics of Mars 2020 Rover Wind Sensors

Environmental factors in Mars atmosphere are a part of the research issues of the future Mars 2020 mission. The new rover surface vehicle will transport different instruments to investigate the geology, biology, and meteorology of Mars. Amongst these instruments, the Mars Environmental Dynamics Analyzer (MEDA) will be dedicated to the measurement of environment parameters. Two wind sensors will be included in the meteorological station MEDA because wind plays a very important role in Martian climate. High-quality wind data are required to build mathematical models of the Mars climate; therefore, powerful techniques are necessary to eliminate aerodynamic perturbations produced by the rover presence over wind measurements. This chapter is dedicated to the characterization of the aerodynamics around the Mars 2020 rover and its interaction with the rover Mars surface vehicle in order to get information to correct wind data coming from Mars

Water droplet deformation and breakup in the vicinity of the leading edge of an incoming airfoil

La presente tesis ha tenido por objeto abordar el problema de la deformación y rotura de gotas debido a la presencia del campo fluido acelerado generado en las inmediaciones de un borde de ataque de un perfil aerodinámico. En la literatura hay numerosos estudios de deformación y rotura de gotas en otras condiciones, como campo fluidos de velocidad constante, cuyos trabajos experimentales se han llevado a cabo principalmente en instalaciones tales como tubos de choque o túneles de viento. Sin embargo la deformación y rotura de gotas en campos fluidos no estacionarios es un problema que no se había abordado todavía. Los campos fluidos no estacionarios, acelerados o decelerados, solo se habían estudiado para esferas solidas o para gotas lo suficiente pequeñas como para despreciar su deformación, siendo además este campo de investigación un campo todavía activo, ya que existen resultados experimentales contradictorios. Por tanto la principal novedad de este trabajo ha sido estudiar la deformación y rotura de gotas en un campo fluido no estacionario. El problema de deformación y rotura de gotas en las inmediaciones de un perfil es de aplicación en el campo aeronáutico, en concreto, en el problema de formación de hielo en alas de aviones debido a la presencia de gotas sobre-enfriadas grandes (también conocidas como SLD). Cuando una gota sobreenfriada impacta en una superficie solida, es posible que se forme hielo en dicha superficie siendo la cantidad y la forma de hielo formado dependiente entre otros factores del tamaño de la gota y del lugar de impacto. Si las gotas se rompiesen antes de llegar a impactar en el ala, como de hecho se ha observado que ocurre, el tamaño de las gotas a impactar cambia bruscamente, lo que podría modificar la forma de hielo en el ala respecto al caso en que las gotas no se rompen. Asimismo, y aunque las gotas no se rompan, el hecho de que se deformen significa que modifican su resistencia lo que se traduce en una variación de su trayectoria y consecuentemente del lugar de impacto. El hecho de que se forme hielo en las superficies aerodinámicas del avión es extremadamente peligroso, ya que modifica la sustentación y la resistencia de las mismas, pudiendo ocasionar accidentes. El problema se abordó de forma experimental realizándose varias campañas de ensayos en las instalaciones del brazo rotatorio de INTA estudiándose gotas de diámetros entre 300 ¸tm y 3.6 mm. En dichos ensayos, se montó un modelo en el extremo del brazo rotatorio de forma que se alcanzaron velocidades del modelo de hasta 90 m/s. Las gotas, en forma de chorro, se dejaron caer en la trayectoria del modelo que se acercaba a las mismas con velocidad constante. Se utilizaron tres modelos de distinto tamaño (radio del borde de ataque de 0.103 mm, 0.070 mm y 0.029 mm) y cinco velocidades de modelo (50 m/s, 60 m/s, 70 m = s, 80 m/s y 90 m/s). Por medio de la técnica de fotografía de sombras, se grabaron las imágenes de vídeo de la deformación y la rotura de las gotas. El campo fluido generado por los modelos se midió previamente usando la técnica PIV. Un software de análisis fue desarrollado para obtener datos cuantitativos de las imágenes sobre la deformación de las gotas y la rotura. Una vez realizado los ensayos, en primer lugar, se realizó un estudio de caracterización del campo fluido generado por el modelo en las gotas, obteniéndose los principales parámetros de flujo implicados en el problema de la deformación y la ruptura de las gotas. Una ley de escala se obtuvo para la deformación. Después, se aplicó el método HOSVD de reducción de datos al problema con el objetivo de profundizar en una visión de la física subyacente. Se construyeron dos tensores: uno que contenía la información de la deformación y otro que contenía el tiempo de ruptura. Estos tensores se utilizaron para extrapolar fuera del tensor y para interpolar en el interior. Y, por último, se propone un criterio de rotura para este tipo de campos fluidos. Las principales conclusiones obtenidas se cuentan en los siguientes párrafos. En la mayoría de los casos analizados durante las campañas experimentales, el tipo de ruptura fue tipo ‘bag y stamen’, excepto en unos pocos casos que se encontró tanto rotura tipo ‘bag’ como rotura tipo ‘shear’. Los efectos no estacionarios debido a la velocidad y aceleración crecientes han demostrado jugar un papel fundamental en los procesos de deformación y rotura de las gotas. Se encontró además que si el cuadrado del tiempo de residencia de la gota por la aceleración se mantiene constante, la deformación de gotas (su relación de aspecto instantánea) depende únicamente de la velocidad de deslizamiento. Esto sugiere que el problema es, al menos, gobernado por un parámetro que implica dos tiempos característicos: el tiempo característico de la variación del campo fluido y el tiempo de residencia de las gotas. Esta tesis pretendía únicamente ser el primer paso en un largo camino hasta poder generar métodos de ingeniería fiables para poder predecir el comportamiento de gotas en las proximidades de las alas de los aviones. Por tanto resultaba interesante obtener bases de datos fiables que pudieran estar disponibles y ser utilizadas en el desarrollo de algoritmos para este fin. Debido a su naturaleza propia, los experimentos involucrados son complejos y caros. En este contexto, el método de descomposición en valores singulares de alto orden (conocido como HOSVD) ha demostrado ser un método bastante adecuado de reducción de datos para este problema. La razón es que permite la generación de bases de datos limpias y densificadas (que se obtienen de conjunto limitado de experimentos) que se pueden usar fácilmente para fines de desarrollo del modelos numéricos. Por último, se ha propuesto un nuevo criterio de rotura para predecir la rotura tipo ‘bag and stamen’, criterio que ha demostrado ser válido para todo el rango de casos experimentales analizados en esta tesis. Este criterio de rotura depende de un tiempo adimensional que es la relación del tiempo característico de deformación de las gotas y el tiempo característico de la variación del campo fluido. ABSTRACT The problem of droplet breakup in the vicinity of the leading edge of an airfoil has been addressed. The aim of this thesis was to study the problem of the deformation and breakup of a droplet that is immersed in a flow field where the velocity and the acceleration that the droplet senses increases continuously. This is a problem that has not been addressed before. Droplet aerobreakup has mainly been studied in shocktube or wind tunnels facilities, where droplet suddenly experiences a high constant air speed. This is in contrast with the problem studied in this thesis, where droplet are initially in a quiescent flow and then the air velocity starts to increase gradually with an acceleration also increasing, until the acceleration and the velocity have reached values that allow for droplet breakup. The problem is then a non-stationary problem and transient effects need to be considered. Accelerating and decelerated non-uniform flow field have only been studied for non-deformable spheres, or droplets that are small enough to neglect deformation and it has proved to be a very complex problem since there still are contradictory results. Therefore, the novelty of this work is to study the aerobreakup of droplets in a non-stationary flow. The problem of a droplet being approached by an airfoil is of special interest in aerospace applications. In particular, when a plane flies through a cloud, the water droplets inside the cloud will experience this flow field velocity when any lift surface such as the wing of the plane approaches. The interest in studying this problem is that these water droplets, when they are supercooled and impinge on lift surfaces of a plane, can create ice on them changing its aerodynamic lift and drag forces and resulting in a change in the performances of the plane, which in turn could cause accidents and the loss of the plane. An experimental investigation has been conducted in the rotating arm facility at INTA covering droplets diameter from 0.3 mm to 3.6 mm. Droplets were generated and allow to fall in the path of an incoming airfoil. Three airfoil sizes (leading edge radius of 0.103 mm, 0.070 mm, and 0.029 mm) and five airfoil velocities (50 m=s, 60 m=s, 70 m=s, 80 m=s and 90 m=s) were used during the test. By means of shadowgraph technique, video images of the deformation and the breakup of the droplets were recorded. The flow field generated by these airfoils was characterized in advance using PIV technique. A tracking software was developed to obtain quantitative data on the droplet deformation and the breakup from the images. During the thesis, first, a characterization of the specific flow field that droplets actually senses when an airfoil is approaching is made and the principal flow parameters involved in the problem of deformation and breakup of droplets are obtained. Then, a data reduction method, the so-called HOSVD, was applied to the problem aiming to provide insight in the underlying physics. Two tensors were constructed: one containing the deformation information and the other containing the breakup time. These tensors were used to extrapolate outside the tensor and to interpolate inside. And finally, the definitions of the onset of the breakup for each mode have been discussed and a breakup criterion equation has been proposed. It was found that in the most of the cases that were addressed during the experimental campaigns, the breakup type was ‘bag and stamen’. In a few cases ‘bag’ and ‘shear’ breakup were also identified. Unsteady effects due to unsteady slip velocity and acceleration profiles play a critical role in the droplet deformation and breakup processes. In the cases addressed in this thesis (continuously accelerating flow) the effect was to anticipate significantly the onset of breakup. It was found that if the flow acceleration profile times the square of the droplet residence time is constant, droplet deformation (its instant aspect ratio) depends on the slip velocity only. this suggests that the problem is, at least, governed by a parameter that involves two characteristic times: the characteristic time of the flowfield variation and the droplet residence time. This thesis has been the first step, only, in a long term development process aiming to generate reliable engineering methods to predict droplet behavior in the vicinity of aircraft wings. This required the availability of reliable databases that can be used for algorithm development purposes. Because of their own nature, the experiments involved are complex and expensive. Then, in this context, it has been found that High Order Singular Value Decomposition is a rather adequate data reduction method for this problem. The reason is that it allows for the generation of clean and densified databases (that are obtained after a limited set of experiments) that can readily be used for model development purposes. A new breakup criterion has been proposed to predict breakup in the ‘bag and stamen’ mode that has prove to be prevailing one in the majority of experimental cases that were addressed in this thesis. Again, the breakup criterion depends on a dimensionless time that is the ratio of the characteristic droplet deformation time to the flow field typical variation time

Characterization of an electrostatic filter prototype for bioaerosol flowmetering for INTA Investigation Aerial Platforms

The characterization of the airborne microorganisms at different altitudes of the atmosphere is usually conducted by means of aerial platforms. It is very interesting to know the biological processes in the atmosphere. However, there are problems associated to the fact that sampling systems are embarked on an aircraft and the low presence of microorganisms at high altitude. A prototype of a new electrostatic filter for bioaersol flowmetering dedicated to biology investigations has been developed. This prototype was designed to be installed on board in aerial platforms of INTA. The experimental characterization of the aerodynamic flow was performed in order to investigate the behaviour of the filter when different air intake widths and different mechanical deflectors are employed. A combination of these impactor with the filters based on industrial electrostatic precipitator technology have been studied. Non-intrusive Particle Image Velocimetry technique has been used to measure the flow field inside the filter when it was running under controlled conditions in laboratory. This study is a first investigation on the flow field of filter for bioaerosol flowmetering to be embarked on an aircraft. The results show the influence of each parameter in the flow field that could be used for further investigations and designs.This research has been partially supported by the Spanish Ministry of Economy and Competiveness (MINECO), under project MICRAS- Scientific missions from manned and unmanned aerial platforms CGL 2015–69758, by the Spanish Ministry of Science, Innovation and Universities under project “Desarollo e implementación de captadores biológicos atmosfericos de altitud: precipitadores electrostáticos de paso unico embarcables en plataformas aereas de investigación” CGL2017-92086-EXP and by the INTA internal project “Termofluidodinámica”

Selection Criteria for Biplane Wing Geometries by Means of 2D Wind Tunnel Tests

This paper presents a study based on wind tunnel research on biplane configurations. The objective of this research is to establish an experimental basis for relationships between the main geometrical parameters that define a biplane configuration (stagger, decalage, gap, and sweep angle) and the aerodynamic characteristics (CL, CD). This experimental study focuses on a 2D approach. This method is the first step towards dealing with the issue, and it allows the variables involved in the tests to be reduced. The biplane configuration has been compared with the monoplane configuration to analyze the viability for implementing the biplane configuration in the field of application for micro air vehicles (MAV). At present, the biplane and other unusual configurations have not been a common design for MAV; however, they do have unlimited future potential. A set of experimental tests were carried out on various biplane configurations at low Reynolds numbers, which allowed the criteria for selecting the best wing configuration to be defined. The results obtained here show that the biplane configuration provides a higher maximum lift coefficient (CLmax) than the planar wing (monoplane). Furthermore, it has a larger wetted surface than the planar configuration, so the parasitic drag increases for the biplane configuration. This research is focused on a drone flight regime (low Reynolds number), and in this case, the parasitic drag (profile drag) has an important role in the total drag of the airplane. This study considers whether the reduction in the induced drag due to three–dimensional configuration (biplanes, box–wings, and joined–wings) can reduce the total drag or if the increase in the parasitic drag is bigger. Additionally, the increase in lift and the decrease in parasitic drag (profile drag) will be studied to determine if they have a greater influence on the performance of the airplane than the increase in structural weight. Further research is planned to be performed on 3D prototypes, with the selected configurations, and applied to nonconventional wing planforms

Design Process and Advanced Manufacturing of an Aquatic Surface Vehicle Hull for the Integration of a Hydrogen Power Plant Propulsion System

This article presents the design and manufacturing of a hydrogen-powered unmanned aquatic surface vehicle (USV) hull. The design process comprised three stages: (1) defining the requirements for a preliminary geometry, (2) verifying the hydrodynamic hull performance using computational fluid dynamics (CFD) simulations, and (3) experimentally validating the hydrodynamic hull performance and CFD analysis results through experimental fluid dynamics in a calm water towing tank. The manufacturing process utilized additive manufacturing technologies, such as fused granular fabrication and selective laser sintering, to produce the hull and other components, including the propeller and the rudder; thermoplastic materials with carbon fiber reinforcement were employed. The experimental results demonstrate that the optimized trimaran hull exhibited low hydrodynamic resistance (7.5 N), high stability, and a smooth flow around the hull (up to 2 m/s). The design and manufacturing of the USV hull met expectations from both hydrodynamic and structural perspectives, and future work was outlined to integrate a power plant, navigation system, and scientific equipment