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Aerodynamics of a small-scale drone propeller in challenging operative conditions
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Experimental Investigation of a Small Drone Propeller Aerodynamics in Forward Flight
Get PDFThe aerodynamic performance of small drones is difficult to predict. Their small-scale propellers operate in a challenging fluid dynamics regime characterized by low Reynolds numbers, where complex transitional phenomena usually occur around the blades' surface. In the present work, an experimental campaign is carried out on a small isolated propeller in forward flight conditions. The main scope is to investigate how the performance and the induced flowfield are affected by the presence of a crossflow, which can be representative of the forward flight condition for a typical drone's propeller. As the crossflow velocity is incremented, considerable increases in thrust and power are measured. The resulting experimental loads are compared with semi-empirical laws derived from the momentum and blade element momentum theories. These laws have found extensive use in the preliminary design of helicopters and are also found applicable to the hereby investigated propeller with appropriate tunings. Furthermore, an analysis of the propeller's wake is conducted via planar particle image velocimetry. Significant differences in terms of flow topology and flowfield statistics are deducted with respect to the hovering condition. Ultimately, the vortices shed from the propeller's blades are identified and characterized, and a focus is posed on the vortices' trajectory and circulation. With respect to the hovering condition, the strongest vortical structures are advected in more confined trajectories, while the weakest structures are instead broken down under the effect of the crossflow
DESIGN OF A PROTOTYPE UNMANNED LIGHTER-THAN-AIR PLATFORM FOR REMOTE SENSING: STRUCTURAL DESIGN AND OPTIMIZATION
Get PDFThis work presents the structural design of a new Remotely Piloted Aircraft System (RPAS) concept for land survey applications. The RPAS Lighter-Than-Air (LTA) platform is equipped with a thrust vectoring control system made of six propellers attached to a single-rib exoskeletal load-bearing structure. The load-bearing structure is optimized to minimize structural mass, maximize payload capability, and meet the airship's operational requirements. A finite element model of the load-bearing structure was developed and analyzed under normal operating conditions of the airship, such as mid-air hovering and parking. Additionally, various failure cases, such as crash landing and control system failure, leading to haphazard operation of the propellers, were considered to simulate extreme load conditions on the airship exoskeletal structure. Airship slenderness was also considered an important design parameter and was optimized to maximize aerodynamic performance. A twin paper describes the other non-structural aspects of the airship design
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Multi-Fidelity Analysis of a Small-Scale Propeller Using VPM Against URANS and Experimental Data
Get PDFInternational audienceThe recent increase in small drones' popularity carries along some critical aspects, especially regarding the evaluation of their aerodynamic performance. Their small-scale propellers operate in challenging fluid dynamics regimes, characterized by complex transitional phenomena typical of low chord-based Reynolds numbers. In this work, an isolated small-scale propeller is analyzed with different techniques in hovering and axial inflow. An experimental campaign was initially conducted, evaluating the propeller thrust and torque with dedicated load sensors and the induced velocity in the wake with the planar PIV. Subsequently, the propeller was simulated with a mid-high fidelity URANS methodology through an overset mesh approach. The SST k-ω turbulence model coupled with the γ-Re_θ transition model was chosen for the purpose, attempting to properly capture the transitional phenomena in the flow. Finally, a further simulation campaign was conducted using the low-fidelity VPM code VULCAINS, in-house-built by ONERA. The code allowed for obtaining accurate results at a very reduced computational cost, with the further advantage of being a meshless method, leading to a very straightforward simulation pre-processing. The outcomes of the three methodologies are remarkably similar, mostly in axial inflow, showing errors under 4% for both thrust and torque coefficients and under 5% for what instead concerns the axial velocity in the wake. On the other hand, a slight mismatch is present in the hovering condition, featured by errors under 8% on the performance coefficients and around 10% to 15% for the axial velocity. Furthermore, the influence of the most relevant input parameters in the VPM code is investigated. The number of vorticity sources shed from the blades per time-step is the most influential parameter, affecting the time-averaged loads, the induced velocity in the wake, and the total computational time.L'augmentation récente de la popularité des petits drones soulève des questions cruciales, notamment en ce qui concerne l'évaluation de leurs performances aérodynamiques. Leurs hélices de petite taille opèrent dans des régimes de dynamique des fluides complexes, caractérisés par des phénomènes de transition complexes typiques des faibles nombres de Reynolds basés sur la corde. Dans ce travail, une hélice de petite taille isolée est analysée à l'aide de différentes techniques en vol stationnaire et en écoulement axial. Une campagne expérimentale a été initialement réalisée, évaluant la poussée et le couple de l'hélice à l'aide de capteurs de charge dédiés et la vitesse induite dans le sillage à l'aide de la PIV planaire. Par la suite, l'hélice a été simulée à l'aide de la méthodologie URANS de moyenne et haute fidélité à travers une approche de maillage superposé. Le modèle de turbulence SST k − omega couplé au modèle de transition gamma − Retheta a été choisi à cet effet, dans le but de capturer correctement les phénomènes de transition dans l'écoulement. Enfin, une autre campagne de simulation a été menée à l'aide du code VPM de faible fidélité VULCAINS V0.5, développé en interne par l'ONERA. Le code a permis d'obtenir des résultats précis à un coût de calcul très réduit, avec l'avantage supplémentaire d'être une méthode sans maillage, ce qui conduit à un prétraitement des simulations très simple. Les résultats obtenus à partir des trois méthodologies se recoupent assez bien, principalement en condition d'écoulement axial, montrant des erreurs très contenues tant en termes de charges moyennées dans le temps que de vitesse induite dans le sillage. En revanche, un léger décalage est présent en condition de vol stationnaire, montrant toutefois des erreurs globalement contenues. De plus, l'influence des paramètres d'entrée les plus pertinents dans le code VPM est étudiée. Le nombre de sources de vorticité émises par les pales à chaque pas de temps se révèle être le plus influent, affectant légèrement les charges moyennées dans le temps, la vitesse induite dans le sillage et le temps de calcul total
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