1,720,981 research outputs found
Validation of a prediction model for aerodynamic noise from aircraft landing gear
No full textThe continued development of quiet engines is now giving rise to situations where airframe noise is comparable with engine noise at approach. The landing gear is a major contributor to airframe noise, and this paper outlines development and testing of a semi-empirical noise model for predicting the benefit of noise control fairings. The model is based on nondimensional source spectra derived from a data base of full-scale tests on A320 landing gear installed in the DNW wind tunnel and is used to predict the noise reduction potential of a variety of fairings installed on the main and noise gears from an A340 aircraft . The model is found to give good agreement with data and this gives confidence that it may be used as an engineering tool to optimise fairing design. The paper also discusses the way in which the model can provide a framework for incorporating CFD data in the design process and also number of factors which complicate the comparison of noise data from wind tunnel and flyover tests
Aerodynamic noise sources on high lift slats and flaps
No full textThe high lift devices used on the wings of civil aircraft to increase lift at low flight speeds are contributors to the overall noise of aircraft at approach. Although there have been a number of recent steps forward in measurement and numerical modelling techniques for these sources there is still more work to be done in understanding the physical and acoustical reasons why they are so dominant. This paper outlines the analysis and interpretation of noise data from an aircraft in flight and the development of a semi-empirical noise model for slats and flaps. Interference patterns observed in the data
indicate that the sound radiation process involves multi-path sound propagation to the observer. A specific outcome of this observation was a notional source model which permitted the separation of noise radiation from the leading and trailing edges of acoustically non-compact flaps, and for slats a separation between two paths radiating from the slat trailing edge either above the slat or through the slat gap. Evidence for the fundamental source mechanisms is combined with standard theory of trailing edge and
leading edge noise on isolated airfoils and acoustic image source techniques to explain why flap noise dominates the forward arc of the aircraft whereas slat noise dominates the rear-arc and hence why these sources are so significant for an observer on the ground
Bluff body noise control using perforated fairings
No full textLanding gears of commercial aircraft make an important contribution to total aircraft noise in the approachconfiguration. Using fairings to shield components from high-speed impingement reduces noise. Furthermore,perforating these fairings has been confirmed by flight tests to enable a further reduction. A fundamental study hasbeen performed to investigate and optimize the benefits of bleeding air through the fairing by application ofperforations. Experiments have been performed with a simplified fairing–strut combination to clarify the influenceof perforations on flow behavior and acoustics. The fairing self-noise is reduced significantly by breakdown of thevortex shedding process, resulting in a reduction of the associated broadband noise level. A redistribution of thevelocities is achieved depending on the applied porosity. However, increasing the porosity can result in adverse noiseeffects due to the bled mass flow washing the strut. Self-noise of the perforations manifests itself at higher frequencies,although scaling of this phenomenon with orifice diameter opens up the possibility to shift it above the upper limit ofthe audible range
Measurement of flow around a flap side with porous edge treatment
No full textWind tunnel experiments were performed to investigate a flap side-edge flowfield. A porous side-edge treatment was applied to a half span flap in an attempt to reduce the flap side-edge noise. Measurements taken were forces, on-surface pressures, particle image velocimetry, hotwire anemometry and on-surface microphones. Oil flow was performed to visualise the on-surface flow. Three potential acoustic sources were identified. The first two sources were the turbulent shear layer reattaching on the side-edge and on the upper surface. A mid-frequency broadband hump was measured by an on-surface microphone at the point of reattachment of the turbulent shear layer on the flap side edge. The third source was a low frequency instability in the vortex due to non-linear vortical interactions upstream of the flap. This instability was measured by a hotwire in the downstream vortex and by an on-surface microphone in the main element flap cove. The effect of the porous side-edge was to reduce the magnitude of vorticity in the turbulent shear layer and the vortex. It was most noticeable in reducing the mid frequency broadband hump. It also had the effect of displacing the vortex further away from the flap surface. This reduced the magnitude of the low frequency perturbations from the unstable vortex that interacted with the solid surface
Modelling landing gear noise with installation effects
No full textThis paper describes continued development and validation of a semi-empirical model of
the aerodynamic noise generated by aircraft landing gears at approach. The model has been
developed with Airbus funding over a number of years1,2 , but recent studies carried out as
part of the EC funded SILENCER project have led to the introduction of a number of new
effects that occur on aircraft in flight. The core of the noise model is based on nondimensional
source spectra derived from a database of full-scale tests on landing gears
installed in the DNW wind tunnel. The new installation effects have been derived using the
results of small-scale model tests3 and by analysis of flight test data4. The model is used to
examine differences between the performance of noise control fairings installed on a landing
gear in a wind tunnel and similar fairings installed on a real aircraft in flight
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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