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Establishment times of hypersonic shock-wave boundary-layer interactions in intermittent facilities
No full textEffect of isolated roughness element height on high-speed laminar–turbulent transition
No full textUnderstanding of the roughness-induced laminar–turbulent transition of supersonic and hypersonic flows is partly challenged by the intricate sensitivities presented by different correlation criteria. We investigate experimentally the effect of height for an isolated roughness element of quadrilateral planform. Heat transfer measurements document the enhancement of roughness-induced disturbances – here the associated heat flux perturbation – along a downstream axisymmetric laminar separation. With increasing element height k k, a gradual intensification in wake disturbance levels is found for subcritical elements ( k/δ k <0.15 k/k<0.15, where δ k k is the undisturbed boundary layer thickness) while elements taller than the effective condition ( k/δ k ⩾0.32 k/k⩾0.32 ) bypass the more moderate transition mechanisms to produce a fully turbulent element wake. Results exhibit high sensitivity to flow properties at roughness height between critical and effective conditions. A reduction in wake disturbance levels with increasing height is documented within 0.23⩽k/δ k ⩽0.32 0.23⩽k/k⩽0.32 . This effect coincides with a decrease in kinematic viscosity at roughness height ν k k(as Mach number at height M k Mk increases from 1.52 to 1.96) and is restricted to elements with strong local separation, whereby the influence of local shear effects is enhanced
Hypersonic interference aerothermodynamics
Get PDFWhen a vehicle travels at hypersonic speeds during launch, cruise or atmospheric re-entry
it is subject to extremely high surface flow temperatures. As well as on the vehicle forebody, extreme heating can take place close to surface protuberances which are almost impossible to avoid in a real flight vehicle. These disturbances interfere with the freestream flow and result in complex viscous interactions which induce a local heat flux augmentation that can become detrimental to the integrity of the vehicle. A greater understanding of these flow phenomena is required.
This thesis develops the understanding of the behaviour of the flow around surface
protuberances in hypersonic vehicles and presents an engineering approach to predict
the location and magnitude of the highest heat transfer rates in their vicinity. To this
end, an experimental investigation was performed in a gun tunnel at freestream Mach
numbers of 8.2 and 12.3 and Reynolds numbers ranging from Reoo/m=3.35xl0 ⁶ to
Reꚙ /m=9.35xl0 ⁶. The effects of protuberance geometry, boundary layer state,
freestream Reynolds number and freestream Mach number were assessed. Further
understanding of the flowfield was obtained through oil-dot visualisations and highspeed
schlieren videos taken at frame rates of up to 50 kHz.
Results show the local interference interaction is strongly three-dimensional and is
dominated by the incipient separation angle induced by the protuberance. In
subcritical interactions - in which the incoming boundary layer remains unseparated
upstream of the protuberance - the highest heating occurs adjacent to the device. In
supercritical interactions - in which the incoming boundary layer is fully separated
ahead of the protuberance - the highest heating generally occurs on the surface just
upstream of it. An exception is for low-deflection protuberances under low-Reynolds
freestream flow conditions in which case the heat flux to the side is greater
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
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