1,721,094 research outputs found
Dataset for The instantaneous structure of secondary flows in turbulent boundary layers
No full textDataset supports:
Vanderwel, Stroh, Kriegseis, Frohnapfel and Ganapathisubramani (2018). The instantaneous structure of secondary flows in turbulent boundary layers. Journal of Fluid Mechanics.
Secondary flows can develop in turbulent boundary layers that grow over surfaces with spanwise inhomogeneities. In this article, we demonstrate the formation of secondary flows in both experimental and numerical tests and dissect the instantaneous structure and topology of these secondary motions. We show that the formation of secondary flows is not very sensitive to the Reynolds number range investigated, and direct numerical simulations and experiments produce similar results in the mean flow as well as the dispersive and turbulent stress distributions. The numerical methods capture time resolved features of the instantaneous flow and provide insight into the near-wall flow structures, that were previously obscured in the experimental measurements. Proper orthogonal decomposition was shown to capture the essence of the secondary flows in relatively few modes and is useful as a filter to analyse the instantaneous flow patterns. The secondary flows are found to create extended regions of high Reynolds stress away from the wall that comprise predominantly sweeps similar to what one would expect to see near the wall and which are comparable in magnitude to the near-wall stress. Analysis of the instantaneous flow patterns reveals that the secondary flows are the result of a non-homogeneous distribution of mid-size vortices.</span
Enhanced three-dimensional particle detection in microcirculation experiments with defocus particle tracking and ghost red blood cells
Full text linkExperimental investigations on the motion of rigid particles in microcirculation environments are still scarce owing to the three-dimensional (3D) motion of the particles and to the particle image masking due to the presence of the red blood cells (RBCs). Despite the recent progress on the 3D tracking of rigid particles in RBC flows with defocus particle tracking (DPT) methods, the problem of particle image masking remains to be solved. Here, we propose, test, and evaluate the use hemoglobin-free RBCs, also known as ghost RBCs, as a replacement for normal RBCs in experiments with rigid particles in microcirculation environments. We performed DPT measurements of a pressure-driven flow of normal and ghost RBC suspensions seeded with rigid particles at three different flow rates. We show that the quasi-transparent appearance of ghost RBCs, as a result of the lack of hemoglobin, eliminates the RBC-induced masking of the defocused particle images and allows to achieve the particle matching standards found in cell-free experiments. In fact, ghost RBC suspensions enable the tracking of the rigid particles across the entire height of the microchannel, which was not possible in normal RBC flows. On a fluid dynamic level, we show that ghost RBC suspensions provide similar conditions to normal RBCs in terms of the velocity of the rigid particles and the rigid particles exhibit similar lateral dynamics in both types of cell suspensions. In essence, the findings from this work demonstrate that ghost RBCs are a well-suited replacement for normal RBCs in experiments aiming at deciphering the motion of rigid particles in microcirculation environments
Volumetric reconstruction of drop impact dynamics by means of color-coded glare points and deep learning
No full textThe present work introduces a method for the volumetric reconstruction of the gas-liquid interface of a droplet impinging on a solid surface from experimental image data by means of deep learning.
Differently colored glare points are used in order to encode three-dimensional information of the phase boundary on the image in addition to a standard shadowgraph.
It is demonstrated that this volumetric information can be successfully reconstructed into a three-dimensional representation of the droplet phase boundary by the proposed neural network
Density measurements in cold plasma discharges by Schlieren method
No full textLAUREA MAGISTRALEL’obiettivo della tesi è investigare il comportamento della densità come variabile ter-
modinamica nell’applicazione dell’attuatore dieletric barrier discharge (DBD) mediante
il metodo sperimentale Schlieren. Lo scopo è quello di verificare, localizzare e quantifi-
care il cambiamento nell’attuazione stazionaria del DBD in condizioni quiescenti. La
densità è richiesta per dedurre modelli empirici e fenomenologici accurati per la forza
esercitata dell’attuatore sul flusso, usato poi come dato d’immissione in simulazioni di
fluidodinamica computazionale sugli attuatori. Gli esperimenti Schlieren sono stati effet-
tuati con due orientazioni diverse di blocco (cutoff) della luce nel punto focale: Il metodo
Schlieren è in grado di rilevare la derivata parziale della densità in direzione normale
all’orientamento del blocco. Coniugando due immagini, realizzate con taglio orizzontale
e verticale, è stato possibile ottenere il gradiente della densità. Il gradiente di densità
è un campo vettoriale potenziale, la densità stessa è uno scalare potenziale. Attraverso
un metodo d’integrazione parziale è stato ricavato il campo potenziale dello scalare den-
sità. Le immagini sono state registrati con una risoluzione di 1392 × 1280 pixel, con due
ingrandimenti: uno di 9.7 × 5.5 mm, per catturare l’origine del cambiamento di densità
e uno di 19.4 × 11 mm per catturare la causa più alcuni degli effetti immediati a valle
del plasma. I risultati rivelano che la densità cambia intorno al 30 ± 10% in prossimità
immediata del plasma. L’area con densità diminuita si allunga ed estende a valle; ciò è
dovuto al trasferimento di moto nel plasma che genera il flusso. Come causa principale
per l’alterazione di densità è stato identificato il riscaldamento del fluido nella zona del
plasma, dovuto alla temperatura elevata degli elettroni presenti nello stesso.This thesis presents the investigation into the behaviour of the thermodynamic state vari-
able density in the application of a dielectric barrier discharge (DBD) actuator by means
of Schlieren experiments. The aim is to verify, to localize and quantify changes in den-
sity for steady actuation of the DBD under quiescent conditions. Density distribution
is required to derive accurate empirical and phenomenological models for the body force
term exerted by the actuator on the flow, used as input in CFD simulations about plasma
actuators. Schlieren experiments are carried out with two different orientations of light-
cutoff in the focal point: The Schlieren method detects the partial derivative of density
in the direction normal to the orientation of cutoff. By combining two Schlieren images,
realized with horizontal and vertical cutoff, the gradient vector field could be obtained.
The density gradient is a potential vector field, and the density is the scalar potential. The
density distribution was retrieved from the gradient by the method of partial integration.
Pictures were recorded with a resolution of 1392 × 1280 pixel, with two different magni-
fications, 9.7 × 5.5 mm to capture the actual cause of density change, and 19.4 × 11 mm
to capture the cause plus some effects downstream. The results show that the density
diminishes for about 30 ± 10% in the immediate plasma zone. The diminished density
zone gets elongated, spread out downstream by the momentum transfer causing the flow.
The main cause for density change was identified as the heating of air, caused by the
elevated temperature of the electrons present in the plasma
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
Strömungsmechanische Bewertung der Umströmung des Gesichtsschildes PlexyCap der Firma Hans Keim Kunststoffe GmbH
Full text linkDie Erstellung dieses Berichts wurde von der Firma Hans Keim Kunststoffe GmbH in Auftrag gegeben, um das firmeneigene, CE-zertifizierte Produkt PlexyCap1,2 als Gesichtsschild hinsichtlich seiner strömungsmechanischen Wirksamkeit zur Minimierung der Tröpfchen- und Aerosolausbreitung vor dem Hintergrund einer Ansteckungsgefahr durch das Virus SARS-CoV-2 zu bewerten. Es sei ausdrücklich darauf hingewiesen, dass alle getroffenen Aussagen und abgeleiteten Schlussfolgerungen in diesem Dokument auf rein kontinuumsmechanischer Grundlage ohne jederart medizinischer und/oder virologischer Expertise basieren. Als Bewertungsgrundlage dienen Hochgeschwindigkeitsaufnahmen einer aerosolangereicherten Hustenwolke, die sowohl von außen aus verschiedenen Richtungen als auch von innen auf das Schild appliziert wurde. Das Bildmaterial wurde von der Firma iLA_5150 GmbH erzeugt und dem ISTM als Bewertungsgrundlage zur Verfügung gestellt
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