| 1. |
- Chernoray, Valery, 1975, et al.
(author)
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Secondary instability of a swept-wing boundary layer disturbed by controlled roughness elements
- 2010
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In: Journal of Visualization. - : Springer Science and Business Media LLC. - 1343-8875 .- 1386-6478 .- 1875-8975. ; 13:3, s. 251-256
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Journal article (peer-reviewed)abstract
- Wind-tunnel data on velocity perturbations evolving in a laminar swept-wing flow under low subsonic conditions are reported. The focus of the present experiments are secondary disturbances of the boundary layer which is modulated by stationary streamwise vortices. Both the stationary vortices and the secondary oscillations of interest are generated in a controlled manner. The experimental data are obtained through hot-wire measurements. Thus, evolution of the vortices, either isolated or interacting with each other, is reconstructed in detail. As is found, the secondary disturbances, initiating the laminar-flow breakdown, are strongly affected by configuration of the stationary boundary-layer perturbation that may have an implication to laminar-turbulent transition control.
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| 2. |
- Chernoray, Valery, 1975, et al.
(author)
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Spatial hot-wire visualization of the Lambda-structure transformation into the turbulent spot on the smooth flat plate surface and riblet effect on this process
- 2010
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In: Journal of Visualization. - : Springer Science and Business Media LLC. - 1343-8875 .- 1386-6478 .- 1875-8975. ; 13:2, s. 151-158
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Journal article (peer-reviewed)abstract
- Evolution of the Lambda-vortex and its transformation into the turbulent spot in a flat plate boundary layer are investigated experimentally. Extensive measurements visualizing the Lambda-structure transformation into the turbulent spot on the smooth and ribbed surfaces of the flat plate are presented. The flow behavior in the course of spatial evolution of the Lambda-structure and turbulent spot is discussed. Specific features of the downstream evolution of Lambda-structure and turbulent spot on the smooth and ribbed surfaces are demonstrated, such as suppression by riblets of the Lambda-vortex transformation into the turbulent spot, appearance of the coherent structures of Lambda-vortex within ensemble-averaged turbulent spot, and oblique waves generation both by the Lambda-vortex and turbulent spot.
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| 3. |
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| 4. |
- Gong, C., et al.
(author)
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The acquisition and measurement of surface waves of high-speed liquid jets
- 2015
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In: Journal of Visualization. - : Springer Science and Business Media LLC. - 1343-8875 .- 1875-8975.
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Journal article (peer-reviewed)abstract
- Abstract: The instability analysis of the liquid jet issuing into ambient air was conducted with an emphasis placed upon the evolution of surface waves of the jet. An experiment was designed to visualize the microscopic morphology on the surface of a liquid jet. A spectral method was proposed to measure wavelength from the obtained jet images. We also discuss key setup parameters that significantly affect the resolution of desired jet features and the accuracy of the spectral measurement. The results show that the liquid jet near the nozzle exit can be divided into a laminar section, a transition section, an instability section, and a turbulence section. Surface wave scales range from 0.06 to 0.11 times of the nozzle diameter with the atomization breakup regime. For the atomization breakup regime, the growth ratio of the surface waves of the instability section is 0.06 which is 1.5 times the value of the second wind-introduced breakup regime and 3 times the value of the first wind-introduced breakup regime. Graphical abstract: [Figure not available: see fulltext.]
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| 5. |
- Kalpakli, Athanasia, et al.
(author)
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Dean vortices in turbulent flows : rocking or rolling?
- 2012
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In: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975. ; 15:1, s. 37-38
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Journal article (peer-reviewed)abstract
- Flows in pipe bends have been studied extensively over the last decades due to their occurrence both in the human respiratory and blood systems as well as in many technical applications. When a fluid flows through a pipe bend an adverse pressure gradient is generated forcing high velocity fluid towards the outer wall which is then replaced by low velocity fluid moving along the wall towards the inner side of the bend. The physical effect is that the high velocity fluid is experiencing a large centrifugal force, resulting in an unstable ‘‘stratification’’ making the high velocity fluid in the centre deflect outwards along the pipe bend, thereby forming two counter-rotating roll cells, so-called Dean vortices. While their behavior in laminar flows has been nicely visualized, the picture of their unsteady behavior in turbulent flows still remains rather blurry, and in fact ‘‘the questions, for example, whether the Dean vortices stay symmetric with respect to the geometric plane of symmetry or whether the strength of the Dean vortices varies with time are hardly addressed’’ (Rütten et al 2005). In the present study, stereoscopic particle image velocimetry has been employed to seize the unsteady behavior of the Dean vortices at the exit of a 90 degree pipe bend at a Reynolds number and Dean number of 34,000 and 19,000, respectively. While the time-averaged flow field shows two symmetrical roll cells, that can be observed both in the streamwise and cross stream velocities, as well as in the streamwise vorticity, the instantaneous snapshots reveal an unsteady behavior where the roll cells are pushing one another alternatively towards the lower or upper half of the pipe, in what could be described as a ‘‘rocking’’ motion of the high speed ‘‘stem’’ in between the roll cells. Hence, the real question is not whether ‘‘to be, or not to be’’ in regards to the instantaneous existence of the Dean vortices in turbulent flows, but rather why, when and how they roll (as their time-averaged counterpart) or rock between the states caught in the presented snapshots.
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| 6. |
- Kalpakli Vester, Athanasia, et al.
(author)
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Combined hot-wire and PIV measurements of a swirling turbulent flow at the exit of a 90° pipe bend
- 2015
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In: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975.
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Journal article (peer-reviewed)abstract
- Measurements of turbulent swirling flow by means of hot-wire anemometry and stereoscopic particle image velocimetry were performed, 0.67 pipe diameters downstream a 90° pipe bend. The flow for a wide range of swirl numbers up to (Formula presented.), based on the angular velocity of the pipe wall and bulk velocity, was investigated and compared to the non-swirling case. The limitations and advantages of using a single hot-wire probe in a highly complex flow field are investigated and discussed. The present paper makes available a unique database for a kind of flow that has been neglected in literature and which is believed to be useful for validation purposes for the computational fluid dynamics community.
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| 7. |
- Kucher, Kostiantyn, 1989-, et al.
(author)
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StanceVis Prime : Visual Analysis of Sentiment and Stance in Social Media Texts
- 2020
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In: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975. ; 23:6, s. 1015-1034
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Journal article (peer-reviewed)abstract
- Text visualization and visual text analytics methods have been successfully applied for various tasks related to the analysis of individual text documents and large document collections such as summarization of main topics or identification of events in discourse. Visualization of sentiments and emotions detected in textual data has also become an important topic of interest, especially with regard to the data originating from social media. Despite the growing interest for this topic, the research problem related to detecting and visualizing various stances, such as rudeness or uncertainty, has not been adequately addressed by existing approaches. The challenges associated with this problem include development of the underlying computational methods and visualization of the corresponding multi-label stance classification results. In this paper, we describe our work on a visual analytics platform, called StanceVis Prime, which has been designed for the analysis of sentiment and stance in temporal text data from various social media data sources. The use case scenarios intended for StanceVis Prime include social media monitoring and research in sociolinguistics. The design was motivated by the requirements of collaborating domain experts in linguistics as part of a larger research project on stance analysis. Our approach involves consuming documents from several text stream sources and applying sentiment and stance classification, resulting in multiple data series associated with source texts. StanceVis Prime provides the end users with an overview of similarities between the data series based on dynamic time warping analysis, as well as detailed visualizations of data series values. Users can also retrieve and conduct both distant and close reading of the documents corresponding to the data series. We demonstrate our approach with case studies involving political targets of interest and several social media data sources and report preliminary user feedback received from a domain expert.
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| 8. |
- Mariani, Raffaello, Assistant Prof. 1981-, et al.
(author)
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On the application of non-standard rainbow schlieren technique upon supersonic jets
- 2020
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In: Journal of Visualization. - : Springer Nature. - 1343-8875 .- 1875-8975. ; 23:3, s. 383-393
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Journal article (peer-reviewed)abstract
- Abstract: A quantitative rainbow schlieren study was conducted on an over-expanded jet at nozzle pressure ratio of 2.8, based on two different schlieren set-ups: the standard z-type and a single-mirror schlieren set-up. The technique used a single, weak focal-length lens placed in the field of view of the system to provide the calibration information required for the extraction of the quantitative data. In the case of the single-mirror set-up, the calibration image required further post-processing procedures to take into account the double refraction experienced by the light. Density gradients were calculated using Abel transform and compared to validated reference data. Results indicate that the single-mirror set-up is able to improve prediction of the density gradient field as compared to the standard z-type schlieren, due to its inherent property of higher sensitivity. The study has shown that the single-mirror set-up performs on average better than the standard z-type system, yielding an overall averaged error of ± 20%, with localized values as low as ± 5% where the shock cell structure is clearly defined, with respect to the validated reference data. At the same time, both systems perform poorly in regions where the flow structure displays poor image contrast. Graphic abstract: [Figure not available: see fulltext.].
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| 9. |
- Milutinovic, Goran, et al.
(author)
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Does visual saliency affect decision-making?
- 2021
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In: Journal of Visualization. - : Springer Nature. - 1343-8875 .- 1875-8975. ; 24:6, s. 1267-1285
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Journal article (peer-reviewed)abstract
- In the present study, we explore potential effects of visual saliency on decision quality in context of multi-criteria decision-making (MCDM). We compare two visualization techniques: parallel coordinates (PC) and scatterplot matrices (SPM). We investigate the impact of saliency facilitated by means of either color or size. The saliency and visualization techniques were factors in our analysis, and effects were evaluated in terms of decision quality, attention, time on task, and confidence. Results show that the quality of choice and attention were comparable for all saliency conditions when SPM was used. For PC, we found a positive effect of color saliency both on the quality of choice and on attention. Different forms of saliency led to varying times on task in both PC and SPM; however, those variations were not significant. A comparison of PC and SPM shows, users spent less time on the task, obtained better decision quality, and were more confident with their decision when using PC. To summarize, our findings suggest that saliency can increase attention and decision quality in MCDM for certain visualization techniques and forms of saliency. Another contribution of this work is the novel suggestion of the method to elicit of users’ preferences; its potential benefits are discussed in the end of the paper.
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| 10. |
- Musleh, Maath, et al.
(author)
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Visual analysis of blow molding machine multivariate time series data
- 2022
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In: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975. ; 25, s. 1329-1342
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Journal article (peer-reviewed)abstract
- The recent development in the data analytics field provides a boost in production for modern industries. Small-sized factories intend to take full advantage of the data collected by sensors used in their machinery. The ultimate goal is to minimize cost and maximize quality, resulting in an increase in profit. In collaboration with domain experts, we implemented a data visualization tool to enable decision-makers in a plastic factory to improve their production process. The tool is an interactive dashboard with multiple coordinated views supporting the exploration from both local and global perspectives. In summary, we investigate three different aspects: methods for preprocessing multivariate time series data, clustering approaches for the already refined data, and visualization techniques that aid domain experts in gaining insights into the different stages of the production process. Here we present our ongoing results grounded in a human-centered development process. We adopt a formative evaluation approach to continuously upgrade our dashboard design that eventually meets partners' requirements and follows the best practices within the field. We also conducted a case study with a domain expert to validate the potential application of the tool in the real-life context. Finally, we assessed the usability and usefulness of the tool with a two-layer summative evaluation that showed encouraging results.
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| 11. |
- Talamelli, Alessandro, et al.
(author)
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"Lock-in" phenomenon in coaxial jets
- 2011
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In: Journal of Visualization. - : Springer Science and Business Media LLC. - 1343-8875 .- 1875-8975. ; 14:4, s. 305-306
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Journal article (peer-reviewed)abstract
- Flow visualizations have been performed in order to study the vortex interactions in the near field of a coaxial jet configuration. Smoke has been injected in the outer stream and a continuous Argon Laser sheet has been used as a light source. Instantaneous pictures have been acquired at a rate of 1 kHz by means of DANTEC Nanosense MK1 camera. In order to remove the background noise the average of all the available images has been subtracted from each snapshot. Different tests have been performed at moderately large Reynolds number, for different velocity ratios, r=Uo/Ui, [1], whereUiandUoare the inner and outer jet velocity, respectively. Three main regimes have emerged depending on the velocity ratio. Although for ru≪1 the coaxial jets dynamics may be related to the independent instability of the inner and outer shear layer (see figure 1a), in this type of configuration (visible for ru≫1 in figure 1c) it is typically the stronger outer shear layer that dominates the near field vortex dynamics, [2]. However, for runearly unitary, and for a thick enough separating wall, a clear vortex shedding behind the separating wall is produced as a result of a global instability mechanism. Figure 1b shows that the generated vortices impose their own dynamics on the entire jet near field synchronizing the instability of the outer shear layer. This ”lock-in” phenomenon can be used as a ”passive” mean, i.e. requiring no energy input, to control the mixing between the two streams and between the jet and the ambient fluid.
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| 12. |
- Vester, Athanasia Kalpakli, et al.
(author)
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Unravelling tumble and swirl in a unique water-analogue engine model
- 2018
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In: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975. ; 21:4, s. 557-568
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Journal article (peer-reviewed)abstract
- The in-cylinder flow prior to combustion is considered to be one of the most important aspects controlling the combustion process in an engine. More specifically, the large-scale structures present in the cylinder, so-called tumble and swirl, before compression are believed to play a major role into the mixing and combustion processes. Their development during the intake stroke and their final strength depend mainly (but not only) on the inlet port design. In the present study, the turbulent large-scale structures during the intake stroke are investigated in a unique water-analogue engine where inlet ports and valve timings can easily be configured and tested. The flow field in the cylinder volume is reconstructed through multi-planar stereoscopic particle image velocimetry measurements which reveal a wealth of vortical structures during the stroke's various phases. The aim of the present paper is to present and show results from a unique setup which can serve as a test bench for optimisation of inlet port designs to obtain a desired vortical pattern in the cylinder after the intake stroke is finished. This setup can simulate the intake stroke in a much more realistic way as compared to a through-flow setup with a fixed valve lift.
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| 13. |
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| 14. |
- Örlü, Ramis, 1977-, et al.
(author)
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The life of a vortex in an axisymmetric jet
- 2011
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In: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975. ; 14:1, s. 5-6
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Journal article (peer-reviewed)abstract
- An axisymmetric jet is produced whenever a fluid is ejected from a round nozzle. The internal and external disturbances present in and surrounding the jet will trigger the formation of Kelvin–Helmoltz waves that are amplified and grow until they saturate and roll up in discrete vortices undergoing different processes such as (vortex) pairing and tearing until they collapse generating a complete turbulent flow. Concerning the evolution of the vortices within the axisymmetric shear layer, a typical scenario, describing the stages in a life of a vortex, is well represented by the flow visualization sequences shown in Fig. 1 as well as the movie in Online Resource 1.
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| 15. |
- Chernoray, Valery, 1975, et al.
(author)
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Influence of an unfavourable pressure gradient on the breakdown of boundary layer streaks
- 2007
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In: Journal of Visualization. - 1343-8875 .- 1386-6478. ; 10:2, s. 217-225
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Journal article (peer-reviewed)abstract
- Breakdown of boundary layer streaks is studied experimentally and compared at zero and adverse (positive) streamwise pressure gradients on a wing under fully controlled experimental conditions. The varicose mode of streak breakdown is found to be a dominant mode in the case of the adverse pressure gradient. A strong influence of pressure gradient upon the development of the streak and the secondary instability is revealed. The unfavourable pressure gradient is shown to alter the critical streak amplitude, the dispersion properties of the streak and the secondary disturbance, as well as attained maximum amplitudes for both the streak and the secondary disturbance.
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| 16. |
- Chernoray, Valery, 1975, et al.
(author)
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Visualization of sinusoidal and varicose instabilities of streaks in a boundary layer
- 2006
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In: Journal of Visualization. - 1343-8875 .- 1386-6478. ; 9:4
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Journal article (peer-reviewed)abstract
- Nonlinear instabilities of boundary layer streaks are investigated experimentally. Extensive measurements visualizing the sinusoidal and varicose instabilities of streaky structures at nonlinear stage of the breakdown process in boundary layer are presented. The flow behaviour in the course of spatial evolution of the streaky structures with a secondary high-frequency disturbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaks are demonstrated, such as transverse and streamwise modulations of the streak by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady Λ-shaped structures localized in space in both cases.
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