1,720,987 research outputs found
Recommended from our members
Measurement of three-dimensional coherent fluid structure in high Reynolds number turbulent boundary layers
Full text linkThe turbulent boundary layer is an aspect of fluid flow which dominates the performance of many engineering systems - yet the analytic solution of such flows is intractable for most applications. Our understanding of boundary layers is therefore limited by our ability to simulate and measure them.
Tomographic Particle Image Velocimetry (TPIV) is a recently developed technique for direct measurement of fluid velocity within a 3D region. This allows new insight into the topological structure of turbulent boundary layers.
Increasing Reynolds Number increases the range of scales at which turbulence exists; a measurement technique must have a larger 'dynamic range' to fully resolve the flow. Tomographic PIV is currently limited in spatial dynamic range (which is also linked to the spatial and temporal resolution) due to a high degree of noise. Results also contain significant bias error.
This work proposes a modification of the technique to use more than two exposures in the PIV process, which (for four exposures) is shown to improve random error by a factor of 2 to 7 depending on experimental setup parameters. The dynamic range increases correspondingly and can be doubled again in highly turbulent flows. Bias error is reduced by up to 40%.
An alternative reconstruction approach is also presented, based on application of a reduction strategy (elimination of coefficients based on a first guess) to the tomographic weightings matrix Wij. This facilitates a potentially significant increase in computational efficiency.
Despite the achieved reduction in error, measurements contain non-zero divergence due to noise and sampling errors. The same problem affects visualisation of topology and coherent fluid structures. Using Projection Onto Convex Sets, a framework for post-processing operators is implemented which includes a divergence minimisation procedure and a scale-limited denoising strategy which is resilient to 'false' vectors contained in the data.
Finally, developed techniques are showcased by visualisation of topological information in the inner region of a high Reynolds Number boundary layer (δ+ = 1890, Reθ = 3650). Comments are made on the visible flow structures and tentative conclusions are drawn
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
Numerical study of unsteady shock/boundary layer interaction
Full text linkThe present work investigates the ability of the Partially-Averaged Navier Stokes (PANS) method to reproduce transonic buffet, occurring on airfoils and wings at transonic regime under specific flow conditions. The designed test case for this analysis is the OAT15A unswept wing at Mach number .M∞ = 0.73 and Reynolds number. Rec = 3 × 106. The three-dimensional flow is studied by accounting for the wind tunnel walls in the experiments of Jacquin et al. [ 1]. The computations on a large-span, confined configuration revealed a strong three-dimensionality of the flow both before and after the buffet onset. The comparison with unsteady Reynolds averaged Navier Stokes (URANS) results showed the benefits of PANS in resolving flow unsteadiness at different flow resolutions, especially on affordable CFD grids, at limited additional cost
Towards Effective Flow Control and Mitigation of Shock Effects in Aeronautical Applications
No full textThis open-access book reports on both experimental and numerical findings from the H2020-funded project TEAMAero (Towards Effective Flow Control and Mitigation of Shock Effects in Aeronautical Applications). It covers novel contributions on improving the fundamental understanding of the physics of shock wave boundary layer interaction, developments in flow control for mitigation of shock effects, and advanced numerical methods for predicting those effects. All in all, this book offers a timely snapshot of research and developments in numerical methods for flow analysis and control, with a special emphasis on high-speed flows. It offers extensive information to both researchers and professionals
Experimental and Numerical Investigations of SBLI and Flow Control on a Transonic Compressor Cascade
Full text linkThe flow through a transonic compressor cascade is inherently unsteady due to the shock-boundary layer interactions (SBLI) on the blade. Despite decades of research, few details are known about the mechanisms that cause such behavior. This chapter presents a multidisciplinary study aiming to elucidate these mechanisms and optimize flow control methods to mitigate their effects. For this purpose, the Transonic Cascade TEAMAero was first optimized and its performance was validated experimentally. The cycle of shock oscillation was then compared using advanced experimental measurement techniques and high-fidelity LES. This comparison revealed a continuous propagation of pressure waves from a point upstream of the trailing edge. The interaction of these waves with the main bow shock at different points of the cycle was then linked to the frequencies observed in the oscillation spectrum. A configuration of this cascade with two roughness patches was finally optimized using a novel procedure developed. The optimal configurations obtained show how the targeted design of these devices can simultaneously mitigate shock oscillations and improve performance. This chapter demonstrates how the combined application of advanced numerical and experimental techniques needs to be intensified as researchers search for a global theory of SBLI in compressor blades
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
- …
