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  • 1.
    Dahl, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hermansson, Roger
    Luleå University of Technology.
    Tiberg, Sven-Erik
    Luleå University of Technology.
    Veber, Pascal
    Luleå University of Technology.
    Use of video-based Particle Image Velocimetry technique for studies of velocity fields in a water heat storage vessel1995In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 18, no 5, p. 383-388Article in journal (Refereed)
    Abstract [en]

    A video-based Particle Image Velocimetry technique has been developed. The technique is particularly suitable for measurement of small velocities, below 3 cm/s. It has proved to be useful for the documentation of non-stationary velocity fields in a scaled-down model of a water heat storage vessel. An ordinary video camera is used to record the in-plane movements of particles in a light sheet in seeded water. The hardware used, the experimental method and the accuracy of the method are discussed. The use of two commercially available software packages (NIH-Image and IGOR) for the analyses is described. Examples of velocity fields are presented, showing that the measuring technique can be used for studies of mixing near the inlet of the storage vessel and exchange of water between the boundary layer and the core.

  • 2.
    Forslund, Tobias O. M.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, I. A. Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Non-Stokesian flow through ordered thin porous media imaged by tomographic-PIV2021In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 62, no 3, article id 46Article in journal (Refereed)
    Abstract [en]

    The 3D flow-fields in a staggered and cubic arrangement of mono-radii cylinders are investigated using tomographic-PIV. The cylinder Reynolds-number is in the range of ≈10 to ≈800 giving an almost complete overview of the transition region. Two pore-scale effects are discovered. The first, visible in the cubic packing, is a spatially alternating lateral velocity field, which has a significant impact on the pressure drop and transversal dispersion. The second effect, present in the staggered array, is an example of a disturbance propagation effect that takes place in the laminar steady region; this manifests as a peculiar and complex flow-pattern. In accordance with other studies, it is shown that Darcy’s law can, from an engineering point of view be valid far beyond the limit for Stokesian flow.

  • 3.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental study of the internal flow in freezing water droplets on a cold surface2019In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 60, no 12, article id 182Article in journal (Refereed)
    Abstract [en]

    The study of a freezing droplet is interesting in areas, where the understanding of build up of ice is important, for example, on wind turbines, airplane wings and roads. In this work, the main focus is to study the internal motion inside freezing water droplets using particle image velocimetry and to reveal if mechanisms such as natural convection and Marangoni convection have a noticeable influence on the flow within the droplet. The flow has successfully been visualized and measured for the first 25% of the total freezing time of the droplet when the velocity in the water is the highest and when the characteristic vortices can be seen. After this initial time period, the high amount of ice in the droplet scatters the PIV light sheet too much and the images retrieved are not suitable for analysis. Initially, it can be seen that the Marangoni effects have a large impact on the internal flow, but after about 15% of the total freezing time, the flow turns indicating increased effects of natural convection on the flow. Shortly after this time, almost no internal flow can be seen.

  • 4.
    Larsson, I. A. Sofia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, B. Daniel
    LKAB, SE-98186, Kiruna, Sweden.
    Experimental study of confined coaxial jets in a non‑axisymmetric co‑flow2020In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 61, no 12, article id 256Article in journal (Refereed)
    Abstract [en]

    Confined, turbulent, coaxial jets in a non-axisymmetric co-flow are studied using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) simultaneously. Eight different cases are measured. Two momentum flow ratios ofthe co-flow are used in the experiment to investigate the effect on the coaxial burner jet behavior and mixing characteristics of the coaxial jet flow and the co-flowing, secondary fluid. In addition, four different momentum flow ratios of the coaxial outer to inner jet are investigated. The objective of the study is to get a deeper understanding of how the flow dynamics affects the entrainment and mixing process in a coaxial jet with a non-axisymmetric, surrounding co-flow. The results show that the introduction of a coaxial stream affects the inner jet and decreases the mixing with the surrounding co-flow; the effect is enhanced as the momentum flow ratio of the coaxial jet increases. The distribution of the secondary, co-flowing fluid controls the shape and direction of the coaxial jet, but does not have a significant impact on the mixing process near the centerline. Practical implications of this investigation are related to the possibility to better control a diffusion flame by introducing acoaxial stream. In this context it is concluded that it is possible to affect the jet development and hence the flame length. The conclusion is based on the assumption that the outer, coaxial stream has a low mass flow, not enough to provide complete combustion, and hence the co-flowing, secondary fluid provides the air needed for the combustion process.

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  • 5.
    Larsson, Sofia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Granström, Reine
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    LKAB.
    PIV analysis of merging flow in a simplified model of a rotary kiln2012In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 53, no 2, p. 545-560Article in journal (Refereed)
    Abstract [en]

    Rotary kilns are used in a variety of industrial applications. The focus in this work is on characterizing the non-reacting, isothermal flow field in a rotary kiln used for iron ore pelletization. A downscaled, simplified model of the kiln is experimentally investigated using particle image velocimetry. Five different momentum flux ratios of the two inlet ducts to the kiln are investigated in order to evaluate its effect on the flow field in general and the recirculation zone in particular. Time-averaged and phase-averaged analyses are reported, and it is found that the flow field resembles that of two parallel merging jets, with the same characteristic flow zones. The back plate separating the inlet ducts acts as a bluff body to the flow and creates a region of reversed flow behind it. Due to the semicircular cross-section of the jets, the wake is elongated along the walls. Conclusions are that the flow field shows a dependence on momentum flux ratio of the jets; as the momentum flux ratio approaches unity, there is an increasing presence of von Kármán-type coherent structures with a Strouhal number of between 0.16 and 0.18. These large-scale structures enhance the mixing of the jets and also affect the size of the recirculation zone. It is also shown that the inclination of the upper inlet duct leads to a decrease in length of the recirculation zone in certain cases.

  • 6.
    Larsson, Sofia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Johansson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    LKAB.
    PIV/PLIF experiments of jet mixing in a model of a rotary kiln2015In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 56, no 5, article id 111Article in journal (Refereed)
    Abstract [en]

    The jet mixing in a downscaled, isothermal model of a rotary kiln is investigated experimentally through simultaneous particle image velocimetry and planar laser-induced fluorescence measurements. The kiln is modeled as a cylinder with three inlets in one end, two semicircular-shaped inlets for what is called the secondary fluid divided by a wall in between, called the back plate, where the burner nozzle is located. The scaling of the burner nozzle between real kiln and model and the corresponding jet flow through it is determined by the Craya–Curtet parameter. Three momentum flux ratios of the secondary fluid are investigated, and the interaction with the burner jet is scrutinized. It is found that the burner jet characteristics, its mixing with the secondary fluid and the resulting flow field surrounding the jet are dependent on the momentum flux ratio. A particular result is that stable shear layers give a more even mixing as compared to a case with shear layers subjected to a more prominent vortex shedding.

  • 7.
    Larsson, Sofia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Tomographic PIV of flow through ordered thin porous media2018In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, no 6, article id 96Article in journal (Refereed)
    Abstract [en]

    Pressure-driven flow in a model of a thin porous medium is investigated using tomographic particle image velocimetry. The solid parts of the porous medium have the shape of vertical cylinders placed on equal interspatial distance from each other. The array of cylinders is confined between two parallel plates, meaning that the permeability is a function of the diameter and height of the cylinders, as well as their interspatial distance. Refractive index matching is applied to enable measurements without optical distortion and a dummy cell is used for the calibration of the measurements. The results reveal that the averaged flow field changes substantially as Reynolds number increases, and that the wakes formed downstream the cylinders contain complex, three-dimensional vortex structures hard to visualize with only planar measurements. An interesting observation is that the time-averaged velocity maximum changes position as Reynolds number increases. For low Reynolds number flow, the maximum is in the middle of the channel, while, for the higher Reynolds numbers investigated, two maxima appear closer to each bounding lower and upper wall.

  • 8. Veber, Pascal
    et al.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hermansson, Roger
    Study of the phenomena affecting the accuracy of a video-based particle tracking velocimetry technique1997In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 22, no 6, p. 482-488Article in journal (Refereed)
    Abstract [en]

    The development of a video-based particle tracking velocimetry (PTV) technique has focused on the problem of the accuracy of this method. The PTV-method can be decomposed into three parts: the recording of the experiment, the image processing and the evaluation of the velocities. The accuracy of each stage has been studied. Inaccuracies due to resolution, length scale, light intensity and distortion of the x and y direction are analysed. One of the main factors influencing the accuracy is the selection of the time difference between frames. During the evaluation of velocities, incorrect identifications of particles may occur. The relation between the time-step of the frames and the percentage of incorrect identifications has been shown. The percentage of false identifications increases with the size of the time-step. The resolution accuracy is however improved when the time-step is increased. An adequate selection of the time-step has to be made to obtain a high resolution accuracy and a limited number of incorrect identifications

1 - 8 of 8
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