abstract: Control algorithm development for quadrotor is usually based solely on rigid body dynamics neglecting aerodynamics. Recent work has demonstrated that such a model is suited only when operating at or near hover conditions and low-speed flight. When operating in confined spaces or during aggressive maneuvers destabilizing forces and moments are induced due to aerodynamic effects. Studies indicate that blade flapping, induced drag, and propeller drag influence forward flight performance while other effects like vortex ring state, ground effect affect vertical flight performance. In this thesis, an offboard data-driven approach is used to derive models for parasitic (bare-airframe) drag and propeller drag. Moreover, thrust and torque coefficients are identified from static bench tests. Among the two, parasitic drag is compensated for in the position controller module in the PX4 firmware. 2-D circular, straight line, and minimum snap rectangular trajectories with corridor constraints are tested exploiting differential flatness property wherein altitude and yaw angle are constant. Flight tests are conducted at ASU Drone Studio and results of tracking performance with default controller and with drag compensated position controller are presented. Root mean squared tracking error in individual axes is used as a metric to evaluate the model performance. Results indicate that, for circular trajectory, the root mean squared error in the x-axis has reduced by 44.54% and in the y-axis by 39.47%. Compensation in turn degrades the tracking in both axis by a maximum under 12% when compared to the default controller for rectangular trajectory case. The x-axis tracking error for the straight-line case has improved by 44.96% with almost no observable change in the y-axis. / Dissertation/Thesis / Real-time Flight Test of Circular Trajectories / Masters Thesis Aerospace Engineering 2020

<p>The continuous trend in gas turbine design towards lighter, more powerful and more reliable engines on one side and use of alternative fuels on the other side renders flutter problems as one of the paramount challenges in engine design. Flutter denotes a self-excited and self-sustained aeroelastic instability phenomenon that can lead to material fatigue and eventually damage of structure in a short period of time unless properly damped. The design for flutter safety involves the prediction of unsteady aerodynamics as well as structural dynamics that is mostly based on in-house developed numerical tools. While high confidence has been gained on the structural side unanticipated flutter occurrences during engine design, testing and operation evidence a need for enhanced validation of aerodynamic models despite the degree of sophistication attained. The continuous development of these models can only be based on the deepened understanding of underlying physical mechanisms from test data.</p><p>As a matter of fact most flutter test cases treat the turbomachine flow in two-dimensional manner indicating that the problem is solved as plane representation at a certain radius rather than representing the complex annular geometry of a real engine. Such considerations do consequently not capture effects that are due to variations in the third dimension, i.e. in radial direction. In this light the present thesis has been formulated to study three-dimensional effects during flutter in the annular environment of a low-pressure turbine blade row and to describe the importance on prediction of flutter stability. The work has been conceived as compound experimental and computational work employing a new annular sector cascade test facility. The aeroelastic response phenomenon is studied in the influence coefficient domain having one blade oscillating in various three-dimensional rigid-body modes and measuring the unsteady response on several blades and at various radial positions. On the computational side a state-of-the-art industrial numerical prediction tool has been used that allowed for two-dimensional and three-dimensional linearized unsteady Euler analyses.</p><p>The results suggest that considerable three-dimensional effects are present, which are harming prediction accuracy for flutter stability when employing a two-dimensional plane model. These effects are mainly apparent as radial gradient in unsteady response magnitude from tip to hub indicating that the sections closer to the hub experience higher aeroelastic response than their equivalent plane representatives. Other effects are due to turbomachinery-typical three-dimensional flow features such as hub endwall and tip leakage vortices, which considerably affect aeroelastic prediction accuracy. Both effects are of the same order of magnitude as effects of design parameters such as reduced frequency, flow velocity level and incidence. Although the overall behavior is captured fairly well when using two-dimensional simulations notable improvement has been demonstrated when modeling fully three-dimensional and including tip clearance.</p>

The continuous trend in gas turbine design towards lighter, more powerful and more reliable engines on one side and use of alternative fuels on the other side renders flutter problems as one of the paramount challenges in engine design. Flutter denotes a self-excited and self-sustained aeroelastic instability phenomenon that can lead to material fatigue and eventually damage of structure in a short period of time unless properly damped. The design for flutter safety involves the prediction of unsteady aerodynamics as well as structural dynamics that is mostly based on in-house developed numerical tools. While high confidence has been gained on the structural side unanticipated flutter occurrences during engine design, testing and operation evidence a need for enhanced validation of aerodynamic models despite the degree of sophistication attained. The continuous development of these models can only be based on the deepened understanding of underlying physical mechanisms from test data. As a matter of fact most flutter test cases treat the turbomachine flow in two-dimensional manner indicating that the problem is solved as plane representation at a certain radius rather than representing the complex annular geometry of a real engine. Such considerations do consequently not capture effects that are due to variations in the third dimension, i.e. in radial direction. In this light the present thesis has been formulated to study three-dimensional effects during flutter in the annular environment of a low-pressure turbine blade row and to describe the importance on prediction of flutter stability. The work has been conceived as compound experimental and computational work employing a new annular sector cascade test facility. The aeroelastic response phenomenon is studied in the influence coefficient domain having one blade oscillating in various three-dimensional rigid-body modes and measuring the unsteady response on several blades and at various radial positions. On the computational side a state-of-the-art industrial numerical prediction tool has been used that allowed for two-dimensional and three-dimensional linearized unsteady Euler analyses. The results suggest that considerable three-dimensional effects are present, which are harming prediction accuracy for flutter stability when employing a two-dimensional plane model. These effects are mainly apparent as radial gradient in unsteady response magnitude from tip to hub indicating that the sections closer to the hub experience higher aeroelastic response than their equivalent plane representatives. Other effects are due to turbomachinery-typical three-dimensional flow features such as hub endwall and tip leakage vortices, which considerably affect aeroelastic prediction accuracy. Both effects are of the same order of magnitude as effects of design parameters such as reduced frequency, flow velocity level and incidence. Although the overall behavior is captured fairly well when using two-dimensional simulations notable improvement has been demonstrated when modeling fully three-dimensional and including tip clearance.

Ce travail de thèse s'inscrit dans la thématique de la pollution particulaire de l'air intérieur et concerne plus particulièrement les phénomènes de remise en suspension liés à l'impact, au niveau du sol, des pas d'une personne qui marche sur un plancher chargé en particules. La première partie présente un état de l'art des connaissances de la pollution particulaire. Les différents paramètres expérimentaux qui influencent la remise en suspension des particules ainsi que les coefficients utilisés pour la quantification du phénomène sont recensés. Les différentes perturbations mécaniques et aérodynamiques générées lors de l'impact d'un pied avec le sol pendant la marche d'une personne sont présentées et comparées. Nous terminons la première partie par une présentation des différents modèles de remise en suspension des particules émanant d'une surface. La seconde partie est consacrée à la présentation de la maquette qui a été mise au point au laboratoire LaSIE à La Rochelle afin d'étudier le dépôt et la remise en suspension des particules par un simulateur mécanique du pas humain depuis un sol chargé en particules. Cette étude a permis de classer les différents types de surfaces utilisées dans le bâtiment en fonction de leurs émissions en particules après l'impact mécanique d'un solide. La troisième partie du travail consiste à mesurer les vitesses de l'écoulement de l'air généré par un simulateur mécanique automatisé du pas humain en différents emplacements. Les mesures de la vitesse ont été effectuées par trois types de méthodes largement utilisées dans le domaine de la mécanique des fluides : deux méthodes de Vélocimétrie Laser (Vélocimétrie par Image des particules et Vélocimétrie Laser Doppler), mais également une méthode d’Anémométrie à Fil Chaud. Ces mesures nous ont permis de trouver la zone de forte vitesse qui correspond à la zone où nous avons une remise en suspension importante. Nous avons également étudié l'influence de l'état de la surface sur les vitesses de l'écoulement générées à proximité du sol suite au mouvement du simulateur mécanique. Ces mesures ont mis en évidence que l'influence de la rugosité de la surface sur la vitesse de l'écoulement généré par le pas est marginale. Finalement, nous avons étudié analytiquement le détachement des particules en utilisant un modèle basé sur le bilan des moments de forces. Des perspectives à la fois sur l'amélioration des deux maquettes mises en place au LaSIE et à l'ERM, ainsi que le développement d'un code numérique pour simuler le pas humain sont présentées et argumentées en conclusion. / This thesis work is part of indoor air particle pollution theme and more particularly the phenomenon of walking-induced particle resuspension. The first part presents a state of the art knowledge of particulate pollution. The different experimental parameters that influence the particles resuspension, as well as the coefficients used for the phenomenon quantification, are identified. The various mechanical and aerodynamic disturbances generated during person walking are presented and compared. We end the first part with a presentation of the different particles resuspension models. The second part is dedicated to present the experiment made on a small scale model developed at the LaSIE laboratory in La Rochelle to study particles deposition and resuspension by amechanical simulator of the human step from a particle-laden soil. This study classified the different types of surfaces used in the building according to their particulate emissions after the mechanical simulator impact. The third part of the work consists of measuring the airflow velocities generated by an automated mechanical simulator of the human footstep at different locations. The velocity measurements have been done in the Royal Military Academy at Brussels (RMA) by three types of methods widely used in the field of fluid mechanics : two methods of Laser Velocimetry (Particle Image Velocimetry and Laser Doppler Velocimetry), but also a method of Wire Anemometry. These measurements allowed us to find the high-speed zone that corresponds to the area where we have a significant resuspension. We also studied the influence the surface roughness on the flow velocities generated near the ground following the movement of the mechanical simulator. We have shown that the influence of the surface roughness on the speed of the flow generated by the pitch is marginal. Finally, we analytically studied the detachment of particles using a model based on the momentum balance. Perspectives on both the improvement of the two models set up in LaSIE and the RMA, as well as the development of a numerical code to simulate the human step, are presented and argued in conclusion.