River flow velocity is critical information for hydraulic and hydrological applications. Monitoring flow fields in near-plant waterways and river reach has wide engineering applications insustainable hydropower generation. For instance, exploring eco-hydraulic concerns such as fish migration, pollutant transport, and river erosion and understanding river floating debris are a few examples of practical applications. Due to complicated geometry and large volumes of natural flows, the measurement task using traditional methods (e.g., velocity propellers, acoustic Doppler velocimetry, with acoustic Doppler current profilers) usually requires extensive investigative work. The measurement procedure also requires contact with waterbody, thus avoiding its use in severe flood conditions. Image analysis approach allows the measurement task to capture the surface-water velocity distribution over a large outdoor area. The main objectives of this research are to (1) evaluate the feasibility of employing multiple cameras in a single measuring system to estimate the flow surfacevelocity and (2) improve the capability to use natural floating materials in river flow observations. The properties of the camera system and particle tracking velocimetry (PTV) algorithm were investigated in a laboratory open channel flow measurement before being deployed for field measurements. The in situ camera calibration methods, which correspond to the two measurement situations, were used to mitigate the instability of the camera mechanism and camera geometry. The artificial tracer particles were deployed to seed the flows. Two photogrammetry-based PTV algorithms are presented regarding different types of employed seeding particles. The first algorithm uses the particle tracking method applied for individual particles, whereas the second algorithm employs correlation-based particle clustering tracking for clusters of small-size particles. The outcomes reveal that the method can offer a reliable and accurate assessment of 3D surface velocity. In river surface velocity measurements, flow seeding is unavoidable in some situations where the water flow is clear, and there are no occurrences of floating materials on the surface. This part of the study focuses on the application of this technique for river velocity measurements using natural surfacefloating patterns. The use of a multiple-camera system provides the ability to perform 3D measurements on the river surface, including surface velocimetry and water surface reconstruction. The pattern-based tracking approach is used to adapt the performance of image measurements on different types of naturalfloating tracers. A comparison of pattern-based tracking with particle tracking reveals that these two approaches are consistent. An analysis of the characteristics of floating patterns is performed to understand their influences on standard deviation of measured velocity. Considerations on practicing image velocimetry in river flows are also discussed.

On demand energy market and favourable government policies to encourage the usage of renewable energy have led to a dramatic increase of grid connected wind, solar, and other power in recent years. Penetration of the power above manageable limit, produced using intermittent energy sources, to meet the demand has induced instable grid operations. On the other hand, the consumers more – or – less expect to be able to draw greater or lesser amount of grid power, whensoever require, at their discretion, and they expect the grid to accommodate this flexibility. Intermittency in the power production and utilisation flexibility to the end users resulted in increased grid incidents. In order to ensure the uninterrupted grid operation one has to take the responsibility to retrieve the grid parameters within operating band before it collapses.Because of speedy and smooth response to the connected grid network, hydroelectric turbines are most frequently used to bring the grid parameters within stable operating band. In a hydro power plant variation in the parameters is detected by a governor and that governs guide vanes angular movement through servo-actuation mechanism. The guide vanes manage mass flow rate flowing to the runner, i.e., the output torque/power. The guide vanes have to react promptly in a very short time to balance the grid. Thus, most of the hydroelectric units are supposed to operate over a larger operating range irrespective of efficiency and the stability, continuous load variation, load rejections, and increased numbers of start-stop cycles.An incompetent opening/closing of the guide vanes during transients induce aperiodic pressure loading on the blade surfaces resulted in cyclic stresses and fatigue. Unexpected transients led to increased wear, shortening the runner life, increased cost of plant operation, and loss of power production. Transients cannot be stopped or avoided but the damage due to the wear and, therefore, runner life may be improved by minimising the unfavourable pressure loading in the turbine through strategic movement of the guide vanes.This motivated to carry out the investigations on hydraulic turbine during transients and study guide vanes operating strategy. The main scope of the licentiate thesis is to identify the change in operating trend of hydraulic turbines due to injection of intermittent energy to the power grid and how it is affecting the turbine operations. The first paper reviews the change in operating trend and consequences to the hydraulic turbines due to changes in the pattern of turbine operation in the recent years. After drawing conclusions from the referred literature, experimental measurements on a model Francis turbine installed at NTNU, Norway, were performed. Both types of, steady state and transient, operational conditions were investigated including pressure measurements. The second paper presents the observations and investigations of steady state measurements and the corresponding numerical simulations. The third paper presents part of the transient experimental investigations; load variations and rejections. Six transient operational conditions were investigated including time domain frequency variation and rotor-stator interaction. The largest pressure variation compared to steady state operation is obtained during load rejection. Preliminary results indicated that appropriate gate closure may minimize large pressure amplitudes in the blade cascade.

Suspensions are composed of mixtures of particles and fluid and are omnipresent in natural phenomena and in industrial processes. While hydrodynamic interactions or lubrication forces between the particles are important in the dilute regime, they become of lesser significance when the concentration is increased, and direct particle contacts become dominant in the rheological response of concentrated suspensions, particularly those close to the maximum volume fraction where the suspension ceases to flow. The mixture of particles and fluid can be seen as a fluid with effective rheological properties but also as a two-phase system wherein the fluid and particles can experience relative motion. By introducing a numerical scheme including both hydrodynamic interactions and grnularlike contacts for dense particle suspensions in overdamped linear flows, we show that contact friction is essential for having DST. Above a critical volume fraction, we observe the existence of two states: a low viscosity, contactless (hence, frictionless) state, and a high viscosity frictional shear jammed state. These two states are separated by a critical shear stress, associated with a critical shear rate where DST occurs. Potential strategies to extend the present methodology to non-spherical particles are also demonstrated and explained for very concentrated suspensions but due to the cumbersome numerical model we will present the results in the future works.

According to the World Health Organisation, nine out of ten people live in places with sub par air quality. Therefore, the study of the treatment of polluted air is from a global point of view of great importance, and a matter of life quality for both humans and as well as animals. There are several di erent methods to treat polluted air, this study focuses on treatment of gas exhausts through ozonation. In the ozonation pro-cess, ozone is injected into the air stream, reacting and degrading the pollutants. The mixing phenomena of ozone in air is highly important for the process, being the focus of this study.To study the mixing, a computational fluid dynamic study was commit-ted on the injection process, with geometries base on industrial applica-tions. The Finite Volume Method was implemented in the simulation software OpenFOAM, on a highly turbulent incompressible flow. To depict the turbulence, Reynolds average RNG k − ε with wall functions and the Large Eddy Simulation (LES) with Wall-Adapting Local Eddy-viscosity (WALE) models were utilized and compared. The mixing is implemented through the transport equation for a passive scalar. For the steady state simulations the Simple-implicit Method for Pressure Linked Equation (SIMPLE) solver was used, and the PIMPLE algo-rithm for the transient cases.First, the flow through a 90 degree elbow pipe bend was investigated. A secondary flow, perpendicular to the pipe, was induced by the pipe bend making the flow three dimensional. Both turbulence models showed great similarities to previous experimental results, and were deemed suÿcient in terms of depicting the flow behaviour. The intensity of the secondary flow depends on the curvature radius, whereas a change in Reynold’s number has negligible e ects on the flow. After the valida-tion, a study of the injection after the pipe bend was conducted, where the position of the injection showed the greatest e ect on the mixing quality. Due to the position being important, it was shown that the secondary flow highly correlates with the quality of mixing, where a high intensity yields a better mixing. / Enligt World Health Organisation, lever nio av tio personer i miljöer med undermålig luft. Därför är en studie på luftrengöringsprocessen av global betydelse, men också en fråga om både människors och djurs livskvalité. Det finns en mängd olika metoder för behnadling av luftföroreningar, denna studie fokuserar på luftbehandling genom ozonering. Under processen reagerar den injicerad ozonet med den förorenade luften och degraderar dem. Blandingsfenomenet av ozone i luft är av stor betydelse för ozoneringen, och därav fokus i denna studie. Strömningsmekaniska beräkningar (CFD) används för att studera injiceringsprocessen, där geometrierna är baserade på industriapplikationer. Finita volymsmetoden var implementerad i simuleringsverktyget OpenFOAM, med ett högst turbulent inkompressibelt flöde. För att återge turbulensen, användes modellerna Reynolds average RNG k − ε med väggfunktioner och Large Eddy Simulation (LES) med Wall Adapting Local Eddy-viscosity (WALE) och sedan jämfördes metoderna med varandra. Blandningen styrs av transportekvationen för en passiv skalär. FÖr statiska tillstånd användes lösningsalgoritmen Simple Implicit Method for Pressure Linked Equation (SIMPLE), medan transienta problem använde algoritmen PIMPLE. En studie av flödet genom en 90 graders rörböj genomfördes först. Ett sekundärt flöde, vinkelrät till röret, var inducerat av rörböjen, vilket skapade ett tredimensionellt flöde. Både turbulensmodellerna visade likheter med tidigare experimentiella studier, och ansågs vara tillräckliga för att återge flödesbeteendet. Intensiteten på det sekundära flödet beror mycket på kurvradien, medan en förändring av Reynolds värdet har försumbar påverkan. Efter valideringen, genomfördes en studie av injicering efter en rörböj, där positionen av själva injiceringen var mest betydelsefull för en hög blandningskvalité. Då postitionen var av stor betydelse, tyder på att en hög blandningskvalité är starkt korrelerat med det sekundära flödet, där en hög intensitet resulterar i en bättre blandning.

The influence of media on piezoelectric pressure transducers are studied experimentally, numerically and analytically. The transient pressure is measured in different types of media in order to discuss the possible effects. The shock tube and the exploding wire system are used in order to generate one step pressure wave and blast wave, respectively. It is shown that placing water or the cellophane tape on the transducer causes larger overshoot than the one in the air. The response of the transducer is modelled by Mass-spring-damper system. This model shows that the larger mass of the transducer is, the larger overshoot becomes. These results imply that the effect of media exists because the effective mass of the transducer is altered. One step transient pressure is generated in the shock tube which is measured by the transducer. The cellophane tape is places on the sensor in order to discuss the influence of change in effective mass. The water is placed instead of the tape to see the effect of different types of media. The transducer with tape shows larger averaged pressure than the one in the air. The transducer with water also shows larger averaged pressure, however, the result is not discussed quantitatively because the sensor with water shows oscillation due to reflections in the water column. The experiment is also conducted with larger pressure amplitude by using converging section. The pressure profiles are obtained by transducer with water which also shows the oscillation due to the shock wave reflection. The blast waves are generated by the exploring wire system where two transducers are mounted at the top and the bottom of the test section just in front of each other. The thin water column is placed one of those transducers. These two sensors should show the same pressure profiles because numerical simulation shows that pressure amplitudes are same over time. However, the sensor with water showed larger amplitude at the beginning. Therefore, it is shown that measuring pressure profiles in water causes measurement error. The behavior of the transducer is studied analytically using Mass-spring-damper system in order to explain why media has the effect on pressure measurement. The change in media is modeled by varying mass of the system. The result shows that as mass goes up, response of the sensor increases which is the same trend as the experimental results. This results imply that the transducers show different pressure profiles depending on the media because the effective mass of the transducer is altered. / Inverkar av olika medier på piezoelektriska tryckgivare undersöks experimentellt, numeriskt och analytiskt. Vi utför mätningar av det tidsberoende tryckförloppet och undersöker inverkan av mediet på resultaten. Stegvisa tryckprofilen alstras i ett strörör och genom explosion av en tunnkoppartråd orsakad av en urladdning från en högspänningskondensator. Vi har visat att en tunn vattenfilm på givaren ger högre överskridande jämfört med luft. Tryckgivaren modelleras som massa kopplad till en fjäder och dämpare. Modellen visar att överskridande av tryckets värden ökar med massan och påvisar inverkan av mediet på märningarna. Vi mäter den stegvis tryckprofilen som alstras i ett strörör. En tunn plastfilm appliceras på tryckgivaren för att deponera lager av olika medier och undersöka inverkan av den effektiva massan på mätningarna. Medeltrycket ökar med enbart plastfilmen på givaren. Resultaten med vattenlagret visar på stora svängningar på grund av stötvågens reflektion i vattenpelaren och vi lämnar den kvantitativa diskussionen till framtida studier. Vi ökar vidare initialtrycket genom en konvergerande sektion av ströröret. Tryckprofiler uppvisar svängningar även i detta fall. Tryckvågsprofilen alstras också genom explosion av en tunn koppartråd genom att leda en stark ström orsakad av en urladdning från en högspänningskondensator. Två tryckgivare placeras på nedre och övre delen av en testkammare. Numeriska beräkningar visar lika värden på tryckgivarna då en tryckvåg passerar. Mätningarna visar dock hörde tryck med en vattenfilm vilket leder till en överskattning av trycket. Vi studerar inverkan av massan på mätningarna genom att variera massan i vår massa-fjäder-dämpare modell. Vår modell påvisar samma trend som experimentella undersökningarna. Sammanfattningsvis har denna undersökning belyst inverkan av tryckgivarens effektiva massa och därmed inverkan av mediet på mätvärdena.

Computational fluid dynamics from large scale thermo-hydraulic simulation in 1D to large eddy simulation in 3D, were applied in this master thesis to study cause of vibrations in a feed-water system downstream the connected pumps. In the first step, the fluid flow of the pumps in RELAP5 simulations was disturbed by the blade passing sinusoidal vibrations to study their propagation in the piping system over time. This simulation resulted in no amplification and resonant in the fluid flow and consequently no standing waves downstream the pumps. However, the mass flow rates were recorded to use later as inputs in RANS model. The main reason for the steady state RANS simulations is to provide boundary conditions for the LES simulations. In the final step, the LES model was implemented locally in the T-pieces and connecting branches to investigate flow- induced vibration and possible vortex shedding oscillations.  The velocity fluctuations were seen right after T-junctions in two system configurations. Despite observing relatively high frequencies of 𝑆𝑡 = 1.4 and 𝑆𝑡 = 1.1 in two different configurations of the piping system, no apparent vortex shedding is seen and velocity fluctuations damp soon and drop to St=0.3 at approximately half a meter from the T-junction.

This thesis investigates a process known as heat pickup which occurs in vehicle cooling system hoses. Heat pickup is an unwanted side effect of temperature differences in a car underhood compartment, whereby excess heat is tranferred into the coolant running through the cooling system hoses, affecting its operating temperature. In addition, the effectiveness of insulation in protecting against this phenomenon is investigated. This is studied experimentally by measuring the temperature change between the inlet and outlet, of coolant flowing through a hose which is subjected to a variety of air temperatures and air flow velocities. In addition to calculating the amount of heat pickup in the coolant, the overall heat transfer coefficient as a function of air temperature and air flow velocity could be quantified. The experiment was conducted by building a miniaturies wind tunnel and placing this in a climate chamber capable of temperatures up to 140°C and circulating the coolant at 20°C and 0.1 l/s. The wind tunnel could reach air velocities up to 6 m/s and therefore, the phenomena was nvestigated at 70, 90 and 120°C  at air velocities between 2 and 6 m/s. In addition, the effect of coolant mass flow rate was investigated in order to see if there was a change in heat pickup due to any transition between the turbulent and laminar regime, since all flow rates were in the vicinity of the critical Reynolds number of 2300 for an internal pipe flow. In addition, a CFD model was developed in Star CCM+ to model the experiment and gain more insight into the underling physics of the problem. The results show that the air velocity and temperature have significant effects on the heat picked up by the coolant, while only air velocity has large effects on the overall heat transfer coefficient. The insulation used in the experiments shows a 35% reduction in the heat picked up by the coolant and a 50% reduction in the overall heat transfer coefficient. The CFD model showed comparable results to the experiment but underestimated the heat pickup by approcimately 10%. These results can be used to improve the accuracy of the 1D CFD modelling of the whole cooling system and in turn, help improve the system's efficiency and reduce energy consumption. / Den här uppsatsen utreder en process känd som "heat pickup" vilket uppstår i kylsystemslangar i fordon. Heat pickup är en oönskad effekt av temperaturskillnader i fordonets motorrum, vilket leder till att värme överförs till kylarvätskan inuti kylslangarna, och påverkar dess driftstemperatur. Dessutom utreds hur väl isolering skyddar mot detta fenomen. Detta studeras experimentellt genom att mäta temperaturförändringen mellan inlopp och utlopp av kylarvätska som flödar genom en kylslang som utsätts för en mängd olika lufttemperaturer och luftflöden. Förutom att beräkna värmeupptagningen i kylarvätskan kunde också den totala värmeöverföringskoefficienten som en funktion av lufttemperatur och luftflöde kvantifieras. Experimentet genomfördes genom att bygga en miniatyrvindtunnel inuti en klimatkammare, som klarar temperaturer upp till 140°C, och cirkulera kylarvätskan vid 20°C och 0.1 l/s. Vindtunneln klarade av att producera vindhastigheter upp till 6m/s, därför undersöktes fenomenet i 70, 90 och 120° för luftflöden mellan 2 och 6m/s. Utöver detta undersöktes också olika massflöden av kylarvätska, för att se om en eventuell övergång från ett laminärt till ett turbulent flöde skulle påverka värmeupptagningen, eftersom att alla massflöden av kylarvätska är i närheten av det kritiska Reynoldsnumret, 2300, för ett internt rörflöde. Dessutom utvecklades en CFD-modell i Star CCM+ för att modellera experimentet och ge större inblick i problemets underliggande fysik. Resultaten visar att både lufthastigheten och lufttemperaturen har en sigifikant effekt på värmeupptagningen i kylarvätskan men endast lufthasigheten har en stor effekt på den total värmeöverföringscoefficienten. Isoleringen som användes i experimenten visar en 35% minskning av värmeupptagningen i kylarvätskan och en 50% minskning av den totala värmeöverföringscoefficienten. CFD-modellen visar jämförbara resultat med experimenten men underskattar värmeupptagningen med omkring 10%. Dessa resultat kan användas för att öka noggrannheten av 1D CFD modelleringarna av hela kylsystemet och därmed också förbättra hela systemets effektivitet vilket skulle minska energiförbrukningen.

This work consists of two parts: the analysis of the operating data collected at Lillgrund between December 2007 and March 2018, and the implementation and evaluation of three wake models. Operational and meteorological data from the Lillgrund wind farm have been analyzed to assess the aerodynamic efficiency and general performance of the farm. Power output, wake losses and array efficiency have been calculated in order to further characterize phenomena related to clustering of wind turbine and garther a database for future model validations. The results of the analysis quantify the intensity of the wake effect at Lillgrund and the power losses due to both wake effect and unavailability of turbines. Moreover, it is found that the array efficiency did not vary through the years. Additionally, effects of atmospheric stratification are evaluated by showing diurnal and seasonal variations of the array efficiency: results are opposite of what was expected, with the wind farm being more efficient at night and during winter. Furthermore, three wake models have been implemented and validated using the developed database: the Jensen model, the Ainslie model and the Gaussian model developed by Bastankhah & Porté-Agel (2014). The objective of the wake effect and power output that is reachable at a very low computational cost for offshore cases. By comparing the results with those of prior works, it can be stated that there is not a substantial diffference in the accuracy of wake models and CFD simulations for the case of Lillgrund.

Turbulent channel flows are of great interest for investigations of modified wall boundary conditions due to their well-understood characteristics and their broad applicability. In a reversal of typical trends, they can often be more difficult to investigate experimentally than to simulate owing to the far-reaching influence of corner effects as well as the need for development lengths in excess of 200 channel half-heights in order to produce high-quality flow. In order to rovice experimental results to compare directly with current and future computational studies conducted in the FSG group, a new experimental channel flow facility has been designed for use with state-of-the-art optical measurement techniques such as planar and stereoscopic µPIV. To further aid in understanding the flows in and around complex surfaces, a water-NaI solution will be used as the working fluid for refractive-index matched experiments. A holistic design approach has been taken, taking into consideration design, manufacturing, operational, and experimental requirements and limitations. The facility has been designed with modularity as a key focus and the channel is subdivided into three interchangeable sections with the capability to support a wide range of experimental set-ups and configurations with minimal modification. To produce a high-quality flow, the channel has an aspect ratio of 20 : 1 and a development length of 288δ preceding the test section. Based on inital design estimates of pressure losses in the system, a 11 kW centrifugal pump has been specified and is projected to allow the channel to reach its maximum design flow velocity of 10 m s¯¹. Reτ of 2300 can be achieved, allowing for investigations well into the turbulent regime which remain within the range of Reynolds numbers that can be resolved in DNS studies. / Turbulenta kanalströmingar är mycket intressanta för undersökningar av modifierade väggrandvilkor på grund av deras väl förstådda egenskaper och allmän tillämpbarhet. MOt typiska trender kan de ofta vara mer komplicerat att undersöka med experimentalla metoder än med strömningsmekaniska beräkningar på grund av påverkan av sekundära flöden i hörn och krav på långa utvecklingssträckor större än 100 kanalhöjder för att garantera strömning av högsta kvalitet. För att ta experimentel data som kan jämföras direkt med aktuella och framtida beräkningsstudier från FSG gruppen, har en ny vattenkanal designats. Kanalen ska utnyttja de senaste optiska mätningsmetoder såsom planar och stetoskopisk µPIV, även med en lösning av vatten och NaI som driftsvätskan för att utföra brytningsindexmatchade experiment. Med ett holistisk utvecklingssätt har tillverknings-, operations-, och experimentella krav och begränsningar beaktats. Kanalen har designats med modularitet som stort fokus och är delad i tre utbytbara sträckor för att tillåta många olika experimentella monteringar och gestaltningar med minimala krav på förändring. För att ge hög strömningskvalitet har kanalen sidförhållande på 20 : 1 och en flödesutvecklingssträcka på 288δ innan mätsträckan. Baserat på inledande beräkning av tryckfallet i hela systemet valdes en 11 kW centrifugalpump. Med den pumpen kommer kanalen att nå sin maximala designhastighet på 10 m s¯¹ vilket ger Reτ = 2300. Detta innebär att undersökningar av turbulenta flöden, inom spännvidden av Reynolds tal som kan simuleras med numeriska metoder, kan utföras.

Luge is an Olympic discipline that challenges athletes to race down an ice track at high velocities. By means of computer simulations, this study exam-ines how posture changes of the athlete affect the aerodynamics to decrease drag. In cooperation with the Swedish National Luge team, all calculations are performed on one of their most prominent athletes, to maximize the ath-lete’s performance on the track. A complete methodology for such individual-based assessments is presented. In particular, a 3D scan of the athlete and the pod is used to perform calculations in Computational Fluid Dynamics (CFD) software. The study found that certain positions decrease drag more effec-tively than others. Shrugging of the athlete’s shoulders tends to decrease drag, whilst an elevation of the athlete’s hips tends to increase it. An analysis of relevant flow structures is presented to explain these differences. To perform well in the Winter Olympics, the Swedish National Luge team is encouraged to adapt this method to all their athletes for maximizing their results. / Rodel är en olympisk gren där idrottare tävlar på en isbana i höga hastigheter. Denna studie undersöker hur förändringar på positionen hos idrottaren på ro-deln, påverkar aerodynamiken för att minska luftmotståndet. I samarbete med Svenska Rodellandslaget, utförs alla beräkningar på en av deras mest fram-stående idrottare för att maximera idrottarens prestation på tävlingar. En 3D-skanning av idrottaren och rodeln skapar en geometri, som används i beräk-ningsströmningsdynamik (CFD) programvaran. Resultaten visar att att detta är en fungerande metod som kan användas för att undersöka aerodynamiken runt en rodel. Studien visade att vissa positioner minskar luftmotståndet mer effektivt än andra. När idrottaren rycker på axlarna tenderar luftmotståndet att minska, medan en höjning av höften tenderar istället att öka luftmotståndet. För att prestera bra under vinter OS och andra tävlingar, bör Rodellandslaget överväga att använda denna metod och resultat på alla sina idrottare för att maximera deras prestation.