| 1. |
- Chernoray, Valery, 1975, et al.
(författare)
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Influence of an unfavourable pressure gradient on the breakdown of boundary layer streaks
- 2007
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Ingår i: Journal of Visualization. - 1343-8875 .- 1386-6478. ; 10:2, s. 217-225
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Chernoray, Valery, 1975, et al.
(författare)
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Secondary instability of a swept-wing boundary layer disturbed by controlled roughness elements
- 2010
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Ingår i: Journal of Visualization. - : Springer Science and Business Media LLC. - 1343-8875 .- 1386-6478 .- 1875-8975. ; 13:3, s. 251-256
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Chernoray, Valery, 1975, et al.
(författare)
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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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Ingår i: Journal of Visualization. - : Springer Science and Business Media LLC. - 1343-8875 .- 1386-6478 .- 1875-8975. ; 13:2, s. 151-158
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Chernoray, Valery, 1975, et al.
(författare)
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Visualization of sinusoidal and varicose instabilities of streaks in a boundary layer
- 2006
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Ingår i: Journal of Visualization. - 1343-8875 .- 1386-6478. ; 9:4
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Eliasson, V, et al.
(författare)
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Shaping converging shock waves by means of obstacles
- 2006
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Ingår i: Journal of Visualization. - KTH Mech, SE-10044 Stockholm, Sweden. : SPRINGER. - 1343-8875 .- 1875-8975. ; 9:3, s. 240-240
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Gong, C., et al.
(författare)
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The acquisition and measurement of surface waves of high-speed liquid jets
- 2015
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Ingår i: Journal of Visualization. - : Springer Science and Business Media LLC. - 1343-8875 .- 1875-8975.
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Kalpakli, Athanasia, et al.
(författare)
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Dean vortices in turbulent flows : rocking or rolling?
- 2012
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Ingår i: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975. ; 15:1, s. 37-38
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Kalpakli Vester, Athanasia, et al.
(författare)
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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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Ingår i: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975.
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Kucher, Kostiantyn, 1989-, et al.
(författare)
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StanceVis Prime : Visual Analysis of Sentiment and Stance in Social Media Texts
- 2020
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Ingår i: Journal of Visualization. - : Springer. - 1343-8875 .- 1875-8975. ; 23:6, s. 1015-1034
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Mariani, Raffaello, Assistant Prof. 1981-, et al.
(författare)
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On the application of non-standard rainbow schlieren technique upon supersonic jets
- 2020
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Ingår i: Journal of Visualization. - : Springer Nature. - 1343-8875 .- 1875-8975. ; 23:3, s. 383-393
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Tidskriftsartikel (refereegranskat)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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