A basic understanding of fluid flow through a porous media facilitates a comprehensive understanding of internal erosion in embankment dams. Hence, it is necessary to reveal the detailed seepage flow, the flow-induced forces acting within the porous media and the fluid flow deformation of the porous media. In order to increase the knowledge of the fluid flow a Computational Fluid Dynamics approach is applied to investigate different flow regimes. The regimes ranges from creeping flow, where a Darcy law formulation is sufficient, via an inertia dominated region, where a non-linear term must be added to the Darcy's law such as the Ergun equation, to the turbulent region, where the full Navier-Stokes equations must be solved including a Reynolds decomposition. Since it is not obvious when these transitions takes place the CFD-simulations are used to calculate the apparent permeability, the Blake-type friction factor and the normal and shear forces for a variety of model geometries. This includes quadratic and hexagonal packing of cylinders as well as spheres. One result is that the Reynolds number, where inertia-effects become significant, varies with the packing and the porosity. For a quadratic arrangement of cylinders this occurs around a Reynolds number about 10 while for a hexagonal arrangement it takes place between 30 and 50 depending on the porosity. Another result is that for quadratic arrangement the turbulent set-up at high Reynolds number gives higher forces than a corresponding laminar set-up regardless of the porosity. For hexagonal packing a turbulent set-up can, however, give lower forces. These ranges, regarding the Reynolds number, have been utilized in order to develop an expression for theoretical limits of the effective diameter and the applied pressure gradient to be applied when designing down-scaled geotechnical experimental setups. Regarding the deformation of the porous media there are several methods that has the potential to model the internal erosion process. One way is a mesh deformation approach where the normal and shear forces acting on the particles generate the motion. This methodology requires that the computational mesh is upgraded in every time-step resulting in rather computational heavy simulations. Another way is to combine CFDsimulations of flow in the vicinity of single particles with Monte-Carlo simulations of a system of a large number of particles by using the fact that the distribution of the stream function follows the known principle of minimal dissipation rate of energy. Main result is that the more compact the system is the larger is the possible relative change of permeability by applying a high flow rate. When applying this technique on a classical geotechnical experimental setup, the No Erosion Filter test, results indicate that the developed model captures the main characteristics of the sought particle transportation, both for a sealing as well as a non-sealing design of the filter and fine combination. / För en övergripande förståelse av inre erosion i fyllnadsdammar är det viktigt att få en grundläggande förståelse av villkoren för flöde genom porösa material. Därför är det nödvändigt att belysa de detaljerade flödesförhållandena, flödesinducerade krafter som verkar inom porösa material och flödesinducerad deformering av porösa material. För att öka kunskapen om dessa flöden är "Computational Fluid Dynamics" -simuleringar ett lämpligt tillvägagångssätt att använda för att undersöka olika flöden. Dessa villkor ger upphov till olika flödesregimer allt från krypande flöde, där en formulering baserad på Darcy's lag är tillräcklig, via en region dominerad av tröghetseffekter, där en icke-linjär term måste läggas till Darcy's lag såsom är fallet i Ergun's ekvation, till den turbulenta regionen, där de fullständiga Navier - Stokes ekvationer måste lösas. Men när dessa övergångar sker är inte uppenbart, därav användandet utav CFD-simuleringar för att beräkna den skenbara permeabilitet, en friktion faktor av Blake-typ och de normala och skjuvkrafter för olika modellgeometrier. Detta inkluderar kvadratiska och hexagonala packningar av cylindrar samt sfärer. Ett resultat är att Reynoldstalet där tröghetseffekterna blir betydande, varierar med packning och porositet. För en kvadratisk packning av cylindrar inträffar detta runt ett Reynolds tal omkring 10 medan för en hexagonal packning äger den rum mellan 30 och 50 beroende på porositet. Ett annat resultat är att för kvadratisk packning med turbulenta inställningar genereras högre krafter vid höga Reynolds tal än en motsvarande laminär inställning och detta sker oavsett porositet. För hexagonal packning kan en turbulent inställning ge lägre krafter. Dessa flödesregimer har använts för att fastställa ett matematiskt uttryck för de teoretiska gränserna gällande den effektiva diametern och lämplig tryckgradient för design utav nedskalade geotekniska experiment.När det gäller deformering utav ett poröst material finns flera metoder som har potential att modellera den inre erosions processen. Ett sätt är en nätdeformationsmetod där normal och skjuvkrafter som verkar på partiklarna genererar rörelse utav det porösa materialet. Denna metod kräver att beräkningsnätet uppdateras i varje tidssteg vilket genererar ganska beräkningsintensiva simuleringar. Ett annat tillvägagångssätt är att kombinera CFD-simuleringar utav flödet i närheten av enstaka partiklar med Monte Carlosimuleringar på ett större system med partiklar. De beräknade parametrarna kombineras på det större systemet där minimering utav dissipationen ger oss ett linjärt ekvationssystem med avseende på strömfunktionen. Från strömfunktionen beräknas fördelningen av krafter på strukturen som ger upphov till en omfördelning av partiklarna, detta för att kunna förutse förändringar i permeabiliteten hos det stora systemet av partiklar. Huvudresultatet är att ju mer kompakt systemet är desto större är den möjliga relativa förändringen utav permeabilitet genom att tillämpa ett högt flöde. Om man tillämpar denna teknik på ett klassisk geotekniskt experiment, No Erosion Filter test, så indikerar resultaten att metoden beskriver huvuddragen vad gäller transport utav partiklar i ett poröst material bestående utav en zon med fint material som kopplar till en filter zon. / <p>Godkänd; 2009; 20091019 (gunhel); DISPUTATION Ämnesområde: Strömningslära/Fluid Mechanics Opponent: PhD/Associate Professor Thanasis D. Papathanasiou, University of Thessaly, Grekland Ordförande: Professor Staffan Lundström, Luleå tekniska universitet Tid: Fredag den 20 november 2009, kl 09.00 Plats: E 243, Luleå tekniska universitet</p>

The solar wind interaction with the terrestrial magnetosphere is a source for many spectacular phenomena on or close the Earth's surface. A key question during the last fifty years have been how the solar wind plasma can enter the terrestrial magnetic shield represented by the magnetosphere and its outermost layer called the magnetopause. This have been the seed for many controversies among researchers throughout the years. Today we know that there are several possibilities for the solar wind to break through the magnetic boundary of the Earth. The main plasma transport mechanism at the magnetopause is called magnetic reconnection, where the magnetic energy stored in the solar wind is converted to kinetic energy through a localized break-down of the ideal frozen-in condition of the magnetic field within the plasma. Since its introduction to the space-physical community in the late 1950's, reconnection research have had its primary focus on understanding the onset mechanisms inside the diffusion region where the solar wind magnetic field is reconnected with the magnetospheric magnetic field. In this thesis work we put the context well out of the diffusion region and focuses on the implications of magnetic reconnection onto the surrounding solar wind plasma, rather than on the main mechanisms which initiates the process. We present solutions for the structure of the plasma flow through the magnetopause surface during conditions of ongoing reconnection. This is done through viscous-resistive reconnection models together with models where finite gyro-radius effects are considered. In order to validate the viscous-resistive model we also couple the analytical solutions with \textit{in situ} measurements made by the Cluster spacecraft fleet. This results in an entirely new way of determining the magnetopause transition layer thickness and the location of the reconnection site from spacecraft data. / Godkänd; 2007; 20070904 (pafi)

Flow with free and rough surfaces near hydropower stations is of interest for both engineering and environmental applications. Here, Computational Fluid Dynamics simulations of free surface flow and flow over rough surfaces in regulated rivers were performed in applications such fish migration, spillway design and flow over rough surfaces as in hydropower tunnels or natural channels. For all the investigated applications it is typical with very large geometrical scales, high flow rates and highly turbulent flow. Modelling boundaries such as free water surfaces and rough walls presents a challenge and was given special attention as well as the treatment of turbulence. Validation of the numerical simulations was performed in all cases with methods such as acoustic measurements with an Acoustic Doppler Current Profiler (ADCP), Acoustic Doppler Velocimeter (ADV) and optical measurements with Particle Image Velocimetry (PIV).Numerical simulations have been used to evaluate the flow downstream the Stornorrfors hydropower plant in Umeälven with regards to upstream migrating fish. Field measurements with an ADCP were performed and the measurements were used to validate the simulations. By adding a fish ladder in the simulations it was possible to investigate the attraction water created from the fishway at different positions and angles. An additional possibility to create better attraction water and improve the conditions for upstream migrating fish was simulated by guiding the spill water from the hydropower dam through a smaller passage from the old river bed.Fish population data from the same location was compared with flow fields from numerical simulations. The population data was compared with variables such as velocity, vorticity and turbulence intensity. A correlation between fish detections and turbulence intensity was shown.Simulations on the spilling from a dam were performed and compared to experimental results from a physical scale model. ADV was used to measure the velocity and validate the simulations. Two different spillway configurations were considered and simulations with both the Rigid Lid model and the Volume of Fluids method were carried out. Water levels, velocities and the shape of the water surface were compared between simulations and experiments. The simulations capture both qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments.A wall with large surface roughness was created by laser scanning a tunnel. One of the side walls was down-scaled and used to create a rough wall in a channel with rectangular cross-section for both a numerical model and an experimental model. Numerical simulations were performed and validated by PIV-measurements in the experimental model.The resolution of the geometry for the rough surface was lowered in two steps and numerical simulations were performed for flow over all three surfaces. The difference in flow fields in the bulk and near wall region was investigated as well as the difference in turbulent quantities which can provide good input for a new model for surface roughness in applications with very large surface roughness and high velocities such as flow in hydropower tunnels or natural channels and rivers. / Godkänd; 2013; 20130425 (aneane); Tillkännagivande disputation 2013-05-29 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Anders G. Andersson Ämne: Strömningslära/Fluid Mechanics Avhandling: Modelling Flow with Free and Rough Surfaces in the Vicinity of Hydropower Plants Opponent: Associate Professor Nils Rüther, Dept of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, Trondheim, Norway Ordförande: Professor Staffan Lundström, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Torsdag den 20 juni 2013, kl 13.00 Plats: E231, Luleå tekniska universitet

Godkänd; 2014; 20140307 (soflar); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Sofia Larsson Ämne: Strömningslära/Fluid Mechanics Avhandling: The Fluid Dynamics of the Cold Flow in a Rotary Kiln Opponent: Forskningsassistent Lisa Prahl Wittberg, Skolan för teknikvetenskap, Mekanik, KTH, Stockholm Ordförande: Professor Staffan Lundström, Avd för strömningslära och experimentell mekanik, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Fredag den 11 april 2014, kl 10.00 Plats: E231, Luleå tekniska universitet / Fastelaboratoriet - VINNEXC

The fluid mechanical field of rough surface flows has been developed ever since the first experiments by Haagen (1854) and Darcy (1857). Although old, the area still holds merit and a surprising amount of information have to this day yet to be fully understood, which surely is a proof of its complexity. Many equations and CFD tools still rely on old, albeit reliable, concepts for simplifying the flow to be able to handle the effects of surface roughness. This notion is, however, likely to change within a not so unforeseeable future. The advancement of computer power has opened the door for more advanced CFD tools such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES). It can be argued that once a given flow situation has been fully accessible by numerical simulations, it is likely to be fully understood within a few years 1 . However, DNS is still limited to small scales of roughness and relatively low Reynolds number which is in contrast with given hydropower conditions today. The hydropower industry annually supplies Sweden with about 45% of its electricity production, and tunnels of various types are regularly used for conveying water to or from turbines within hydropower stations. The tunnels are a vital part of the system and their survival is of the essence. Depending on the manner of excavation, the walls of the tunnels regularly exhibit a roughness, this roughness may range from a few mm to m, which is true especially if the tunnel have been subjected to damage. For natural roughness e.g. hydropower tunnels, there is no clear way to distinguish between rough surface flows and flow past obstacles. Yet, to be able to distinguish between the two cases has proven to be important. This work is aimed to increase the understanding of how the wall roughness affects the flow, and how to treat it numerically. Paper A employs the use of pressure sensors to evaluate local deviations in pressure as well as head loss due to the surface roughness. Paper B is aimed at using PIV to evaluate the flow using averaging techniques and characteristic length scales. Paper C Further investigates the data from the PIV and pressure measurements and Evaluates the possibility to use basic but versatile turbulence models to evaluate the flow in such tunnels.

Iron ore pellets are a highly refined product supplied to the steel making industry for use in blast furnaces or direct reduction processes. The use of pellets offers many advantages such as customer adopted products, transportability and mechanical strength yet the production is time and energy consuming. Being such, there is a natural driving force to enhance the pelletization in order to optimize production and improve quality. The aim with this thesis is to develop numerical models with which the drying zone of an induration furnace can be examined and optimized. To start with, a continuous model of velocity and temperature distribution in the up-draught drying zone, without regard to moisture transport, is developed with aid of Computational Fluid Dynamics (CFD). The results show a rapid cooling of air due to the high specific surface area in the porous material. With the global model an overall understanding of heat transfer is gained, but the heat and moisture transport should also be investigated on a smaller scale in order to account for small scale phenomena such as turbulence and dispersion. Drying of a bed of iron ore pellets is therefore considered by modeling a two-dimensional discrete system of round pellets. The system is divided by modified Voronoi diagrams and the convective heat transfer of hot fluid flow through the system including dispersion due to random configuration of the pellets is modeled. The results show that the temperature front advances much faster in the gaps between pellets than in the interior of the pellets even if all the heat energy of the air goes in heating of the pellets initially. Decrease of temperature is possible for low dew points of the input air due to evaporation. If the dew point temperature is higher than the temperature of the pellets on the other hand, there is slight condensation of the steam at the beginning of the process and the temperature increases faster than it would for pure thermal heating. An uneven distribution in temperature and moisture content between pellets is furthermore displayed in the discrete system. This phenomenon is related to the natural dispersion occurring in random system of pellets.To further investigate drying of individual pellets, forced convective heating of a cylindrical porous pellet with surrounding flow field taken into account is first examined. A model with properties similar to that of an iron ore pellet is numerically investigated and with interface heat transfer condition provided by CFD, the simulations show an increased heating rate for the porous cylinder when compared to a solid. The most plausible explanation to this is that there is less solid to heat up for the porous medium since the porous cylinder behaves as if it was impermeable from a fluid flow point of view. With diffusive liquid transport inside the two-dimensional pellet and corresponding evaporation at the surface, simulations of drying show an initial warm up phase with a succeeding constant rate drying phase. Constant drying rate will only be achieved if the surface temperature is constant, i.e. if it has reached the wet bulb temperature. The falling rate period will subsequently start at the forward stagnation point when the local moisture content approaches zero, while other parts of the surface still provide enough moisture to allow surface evaporation. The phases will thus coexist for a period of time. Experiments are carried out in order to examine the drying behavior of a single iron ore pellet with main goal to retrieve data for validation of the computational drying models. The experiments are performed with two inlet temperatures and one pellet from the experiments is scanned by an optical scanning equipment. In order to investigate the influence of surface irregularities and overall geometry on drying, simulations of the first drying period are compared for: 1) a scanned pellet 2) an oval pellet resembling the experimental one with equivalent volume 3) a spherical pellet with equivalent volume. The results show that the local moisture content at the surface is influenced by both surface irregularities and overall geometry. A smooth surface will decrease the local variation of moisture while a spherical geometry will, compared to an oval, increase the difference. A diffusive model taking into account capillary flow of liquid moisture and internal evaporation is developed to account for the whole drying process and simulations of the scanned pellet are validated with good agreement. The result clearly shows four stages of drying; i) evaporation of liquid moisture at the pellet surface, ii) surface evaporation coexisting with internal drying as the surface is locally dry, iii) internal evaporation with completely dry surface and iv) internal evaporation at boiling temperatures. A moisture front moving towards the core of the pellet will start to develop at the second drying stage and the results show that the front will have a non-symmetrical form arising from the surrounding fluid flow. With the developed drying model, simulations are then carried out on a spherical pellet with aim to investigate how the inlet air humidity affects drying. The results indicates that the effect of air dew point arise from the start of the first drying period, i.e the surface evaporation period, while the difference is reduced at the end of the period due to a prolonged stage of constant rate drying attained at high dew points. The wet-bulb temperature is increased with humidity and condensation will occur if the pellet surface temperature is below the dew point. Furthermore it is found that the moisture gradients at the surface and inside the pellet are increased with drying rate. / Godkänd; 2010; 20101103 (annlju); DISPUTATION Ämnesområde: Strömningslära/Fluid Mechanics Opponent: Professor Graham Nathan, The University of Adelaide, Australia Ordförande: Professor Staffan Lundström, Luleå tekniska universitet Tid: Onsdag den 8 december 2010, kl 09.00 Plats: F431, Luleå tekniska universitet

Iron ore pellets are a highly refined product and for companies such as LKAB it is important to constantly improve the pelletization in order to enhance production and improve product quality. A long term goal has been established to develop and considerably refine tools and techniques with which the drying zone of a pelletizing plant can be optimized. The aim with this research project is to numerically investigate how material and processing parameters influence the drying. This will be applied to several scales: i) The constituents of the pellets and their properties and geometry. ii) The geometry of the pellet, their permeability and size distribution. iii) The geometry of the bed and the processing conditions including the state of the air (ex. humidity, temperature and velocity). To start with, a pellet bed model of velocity and temperature distribution in the up-draught drying zone without regard to moisture transport is developed with aid of Computational Fluid Dynamics (CFD). Results from simulations show a rapid cooling of air due to the high specific surface area in the porous material. Following this work, heat and mass transport within a single pellet during drying is modeled. Heat transfer and convective transport of water and air through the capillaries of the porous media is computed and vaporization by boiling is taken into account. A sensitivity analysis shows that it is important to use a realistic value of the convective heat transfer coefficient when the vaporization of water is a dominating drying mechanism while the temperature of the solid and capillary movement of water is not influenced to the same extent. The derived model is applicable to a number of numerical set up such as a single pellet placed in infinite space. To further develop a single pellet model, forced convective heating of a porous media with surrounding flow field taken into account must first be examined. Therefore, a two dimensional model with properties similar to that of an iron ore pellet is numerically investigated. With interface heat transfer condition provided by CFD, the heat transfer and fluid flow around and within a porous cylinder is examined. The results lay foundation of future development of a single pellet drying model where heat and mass transfer models are combined and coupled to the surrounding flow field. / Godkänd; 2008; 20080428 (ysko)

<p> Microbubbles and droplets are nanometer to micron size biocompatible particles which are primarily used for drug delivery and contrast imaging. Our aim is to broaden the use of microbubbles from contrast imaging to other applications such as measuring blood pressure. The other goal is to develop in situ contrast agents (phase shift droplets) which can be used for applications such as cancer tumor imaging. Therefore, the focus is on developing and validating the concept using experimental and theoretical methods. Below is an overview of each of the projects performed on droplets and microbubbles. </p><p> Phase shift droplets vaporizable by acoustic stimulation offer many advantages over microbubbles as contrast agents due to their higher stability and possibility of smaller sizes. In this study, the acoustic droplet vaporization (ADV) threshold of a suspension of PFP droplets (400-3000nm) was acoustically measured as a function of the excitation frequency by examining the scattered signals, fundamental, sub- and second-harmonic. This work presents the experimental methodology to determine ADV threshold. The threshold increases with frequency: 1.25 MPa at 2.25 MHz, 2.0 MPa at 5 MHz and 2.5 MPa at 10 MHz. The scattered response from droplets was also found to match well with that of independently prepared lipid-coated microbubble suspension in magnitude as well as trends above the threshold value. Additionally, we have employed classical nucleation theory (CNT) to investigate the ADV, specifically the threshold value of the peak negative pressure required for vaporization. The theoretical analysis predicts that the ADV threshold increases with increasing surface tension of the droplet core and frequency of excitation, while it decreases with increasing temperature and droplet size. The predictions are in qualitative agreement with experimental observations. </p><p> A technique to measure the ambient pressure using microbubbles was developed. Here we are presenting the results of an in vitro study aimed at developing an ultrasound-aided noninvasive pressure estimation technique using contrast agents--Definity&reg;, a lipid coated microbubble, and an experimental PLA (Poly lactic acid) microbubbles. Scattered responses from these bubbles have been measured in vitro as a function of ambient pressure using a 3.5 MHz acoustic excitation of varying amplitude. At an acoustic pressure of 670 kPa, Definity^&reg; microbubbles showed a linear decrease in subharmonic signal with increasing ambient pressure, registering a 12dB reduction at an overpressure of 120 mm Hg. Ultrasound contrast microbubbles experience widely varying ambient blood pressure in different organs, which can also change due to diseases. Pressure change can alter the material properties of the encapsulation of these microbubbles. Here the characteristic rheological parameters of contrast agent Definity and Targestar are determined by varying the ambient pressure (in a physiologically relevant range 0-200 mmHg). Four different interfacial rheological models are used to characterize the microbubbles. Both the contrast agents show an increase in their interfacial dilatational viscosity and interfacial dilatational elasticity with ambient pressure. </p><p> It has been well established that liposomes prepared following a careful multi-step procedure can be made echogenic. Our group as well as others experimentally demonstrated that freeze-drying in the presence of mannitol is a crucial component to ensure echogenicity. Here, we showed that freeze-dried aqueous solutions of excipients such as mannitol, meso-erythritol, glycine, and glucose that assume a crystalline state, when dispersed in water creates bubbles and are echogenic even without any lipids. We also present an explanation for the bubble generation process because of dissolution of mannitol.</p><p>

Computational Fluid Dynamics (CFD) are used to investigate two speech phenomena. The first phenomenon is the English bilabial plosive /pa/. Simulations are compared with microphone recordings and high speed video recordings to study the penetration rate and strength of the jet associated with the plosive /pa/. It is found that the dynamics in the first 10ms of the plosive are critical to penetration rate, and the static simulation was not able to capture this effect. However, the simulation is able to replicate the penetration rate after the initial 10ms. The second speech phenomenon is the English fricative /sh/. Here, the goal is to simulate the sound created during /sh/ to understand the flow mechanisms involved with the creation of this sound and to investigate the simulation design required to predict the sound adequately. A variety of simulation methods are tested, and the results are compared with previously published experimental results. It is found that all Reynolds-Averaged Navier-Stokes (RANS) simulations give bad results, and 2D Large Eddy Simulations (LES) also have poor results. The 3D LES simulations show the most promise, but still do not produce a closely matching spectra. It is found that the acoustic analogy matches the direct measurements fairly well in 3D simulations. The studies of /pa/ and /sh/ are compared and contrasted with each other. From the findings of the studies, and using theoretical considerations, arguments are made concerning which CFD methods are appropriate for speech research. The two studies are also considered for their direct applications to the field and future research directions which might be followed. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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