1,721,141 research outputs found
Vorlesung Basics of Aeroacoustics
Get PDFDas Vorlesungsmanuskript führt in das Gebiet Aeroakustik ein. Es befähigt Studierende, sich selbstständig in der Fachliteratur zum Thema Aeroakustik zurecht zu finden. Die Vorlesung setzt auf Grundlagenwissen aus den Ingenieurwissenschaften auf, die mit Abschluss der Bachelorausbildung vorliegt. Der erste Teil gibt einen Überblick über alle wichtigen Grundbegriffe der klassischen Akustik. Der zweite Teil enthält die Generalisierung auf aeroakustische Fragestellungen. Das Konzept aeroakustischer Analogien wird bis hin zur Ffowcs-Williams und Hawkingsgleichung ausgearbeitet und auf technische Beispiele angewendet.
The lecture notes introduce into the topic of aeroacoustics. It enables students to self-dependently orient themselves in the technical literature. The lecture draws on basic knowledge gained with a bachelors degree in engineering. The first part provides an overview about all important technical terms of classical acoustics. The second part contains the generalization on aeroaocustic problems. The concept of aeroacoustic analogies is elaborated up to Ffowcs-Williams and Hawkings equation and is applied to technical examples
Evaluation of the Noise Reduction Potential of a Krueger Flap High-Lift device via the Lattice Boltzmann Method
No full textMain objective of this work is to conduct Direct Noise Computation of high-lift wings using wall-modeled LES with LBM. For this purpose, we employ an industrial LBM software ProLB. In our previously reported work, we presented a quantitatively successful validation of a conventional high-lift wing (DLR/ONERA F16). This study carries forward our high-lift noise
investigation, now with a Krueger flap as an alternative high-lift device that has been proposed elsewhere for the laminar wing concepts. Aeroacoustically, in the absence of noise-generating mechanisms that are typically present at the conventional slat i.e. interacting and impinging
shear layers, this design provides a potential for noise reduction. For this study, we use two different Krueger flap designs: reference and aerodynamically optimized Krueger. Reference Krueger has a short chord while the optimized Krueger has a long chord. These multi-element,
unswept high-lift wings with deployed Krueger flap and flap are resolved on a mesh with 5%clean chord length spanwise extent. Periodic boundary condition is applied along the spanwise direction. For the relative accuracy, the time-averaged near field WM-LES results for both the Krueger flap variants are compared with the RANS. Far field acoustic comparison is carried out between the conventional slat (F16) and both the Krueger leading edge devices. Optimized Krueger shows a noise reduction potential over the reference Krueger and conventional slat based design. Further noise reduction potential is observed when the cavity for Krueger flap to stow back is closed in the simulation. It is found that the stowage cavity contributes to the overall noise radiation for frequencies higher than 3 kHz. Additional improvement towards tackling of the periodicity effect in the direct noise computation of high-lift approaches is reported. Periodicity introduces a cut-on type jump in the pressure spectrum. A new approach is introduced for the specific spanwise periodic setup that cancels excess energy induced by the
additional cut-on modes
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
Numerische Simulation externer und interner Strömungsgeräusche von Fahrzeugkomponenten
Get PDFA wide range of numerical methods have been developed in the last years to assess aeroacoustic problems. This work focuses on the possibility of using stochastic reconstruction of acoustic sources to simulate the noise generated by external and internal flows. The simulations are performed with the aeroacoustic code PIANO developed at the DLR Braunschweig. Two typical automotive applications were chosen to assess the capacity of such methods.
The first application consists in the computation of the acoustic field generated by the flow in 2D duct containing a flat plate. Two computational aeroacoustic methods have been used. The first method is based on the LEE, a single-test vortex is injected in the mean flow to interact with the geometry. The second method is based on the APE and a stochastic sound source modelling. The frequency and mode representation computed by both methods are in good agreement with the experiment.
The second application concerns the broadband noise induced by flow interacting with an automotive rain gutter. Two different profiles of rain gutter have been tested in wind tunnel. Steady and unsteady flow simulations have been computed. Four different computational methods have then been used to predict the flow-induced noise of an automotive rain gutter. The first two methods are based on different wave operators to compute the acoustic field radiated by an unsteady flow field. The first method is the Lighthill's Equation (Actran/LA) while the second method is based on the APE system. The two other methods are the same methods as those used for the first application: the injection of a single test-vortex in the flow and the stochastic sound source modelling (RPM). The first two methods delivered similar results but remained high sensitive to the quality of the acoustic sources computed by CFD. A good agreement was found between the RPM modelling and the experiment.Zahlreiche numerische Methoden für Aeroakustik wurden in den letzten Jahren entwickelt. Diese Arbeit fokussiert sich auf die Möglichkeit von stochastischen Methoden, um die akustischen Quellen aus gemittelten Strömungsfeldern zu rekonstruieren und das durch Um- und Durchströmung erzeugte Geräusch zu simulieren. Die Simulationen wurden mit der Simulationssoftware PIANO vom DLR Braunschweig durchgeführt. Zwei für die Automobilindustrie typische Anwendungsfälle wurden ausgewählt, um die Möglichkeit der Methode für solche Fälle zu testen.
Im ersten Fall wurde das akustische Feld einer ebenen Platte in einem 2D Kanal berechnet. Zwei numerische Methoden wurden dafür benutzt. Die erste Methode basiert auf den LEE Gleichungen: ein Einzel-Testwirbel wird in die mittlere Strömung injiziert, um mit der Geometrie zu interagieren. Die zweite Methode basiert auf den APE. Bei diesem stochastischen Modell, werden die akustischen Quellen aus mittleren Strömungsgrößen rekonstruiert. Die von beiden Methoden berechnete Frequenz und Moden Darstellung der Parker Resonanzen stimmen gut mit den experimentellen Daten überein.
Der zweite Anwendungsfall ist der induzierte Breitbandlärm, der bei der Umströmung automobiler Wasserfangleisten entsteht. Zwei unterschiedliche Profile wurden im Windkanal getestet. Dabei werden zuerst stationäre und transiente Simulationen eingesetzt. Im zweiten Teil der Arbeit werden vier unterschiedliche Methoden benutzt, um die strömungsinduzierten Geräusche der Wasserfangleisten zu berechnen. Die erste Methode basiert auf der Lighthill-Gleichung (Actran/LA). Die zweite Methode basiert auf den APE Gleichungen. Die zwei weiteren Methoden sind die Injektion eines Einzel Testwirbels und die RPM Turbulenz Modellierung. Die ersten zwei Methoden liefern ähnliche Ergebnisse, aber zeigen eine hohe Sensitivität zur Qualität der zu Grunde liegenden CFD Simulationen. Sehr gute Übereinstimmung zwischen dem RPM Modell und den Experimenten wurden gefunden
Airframe Noise
No full textThese lecture notes are meant to give an introduction into airframe noise at transport aircraft. The purpose is to provide the reader with the necessary background knowledge for understanding the source mechanisms attributed to the various airframe noise sources. The purpose is not to provide an extended review on experimental or computational work
in the field of airframe noise. The focus of the lecture is to convey a general understanding of the essential source physics at the most dominant airframe noise components. These are
the landing gears, slotted slats, flap side edges and some installation effects. A considerable part of the lecture refers to the large set of findings about all aspects of airframe noise
obtained by Dr. Werner Dobrzynski, a retired colleague of the author at DLR
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
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