This thesis has been a part of Forsmarks Kraftgrupp AB's evaluation of a turbulence model used in simulation of turbulent flow called PRNS (Partially Resolved Numerical Simulation). This model has promising properties and may be of use in saving computational resources. The purpose of this thesis was to analyze this model and compare it with industrially applied models such as k-omega SST and LES (Large Eddy Simulations). PRNS works as a hybrid of the k-omega SST and DNS (Direct Numerical Simulation) where a constant, RCP (Resolution Control Parameter) with a value between 0 and 1 are selected. This constant is then used in the calculations and determines the behavior of the simulation. When RCP is set to zero the equation are the same as for a DNS simulation and when RCP is set to one the equations for k-omega SST is solved. In this report four different PRNS models have been used, three where RCP was given a constant value (0.1, 0.4 and 0.6). In the fourth model RCP is calculated from the flow field variables The models have been compared to an experiment from 2008 and simulations have been made to resemble the experiment. In the experiment a Particle Image Velocimeter (PIV) was used as method of measurement. From the experimental report data such as velocity (U), turbulent kinetic energy (k) and standard deviation (URMS) have been obtained and have formed the basis for comparison. The models have been simulated in two different software programs: OpenFOAM and Fluent. The data have thereafter been post processed in the software programs MatLab and ParaView, to be compared with experimental data. The results of the simulations have shown that PRNS models generally show a good accordance with experimental data. In particular, PRNS models with constant RCP have shown good results, however, there are some discrepancies. The PRNS model with varying RCP has in most cases showed the largest deviation from experimental data but also a deviation from the other models, including the reference models. Due to the design of the mesh (coarse) further evaluation of the PRNS models will be needed. First, simulate with a finer mesh, but also more complex geometries should be simulated in order to sort out PRNS strengths and weaknesses and thus determine if the model can be used in the daily work at Forsmarks Kraftgrupp AB.

The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold. / Tidigare studier visar att ett roterande flöde kan ge en mer likformig hastighetsfördelning och en lugnare fyllning i både göt- och stränggjutning av stål. De befintliga metoderna för att generera ett roterande flöde har vissa begränsningar. En ny metod för att generera det roterande flödet, en så kallad TurboSwirl, föreslogs nyligen. I detta arbete undersöktes ett konvergent munstycke med olika vinklar för att se hur detta påverkade det roterande flödet som genererades i anordningen. Resultaten visar att skjuvspänningen i systemet kan reduceras genom att ändra munstyckets vinkel mellan 40º till 60º. En lägre maximal axiell hastighet kan också uppnås med en mindre konvergent vinkel på munstycket. Det är även möjligt att påverka den maximala axiella hastigheten och skjuvspänningen i systemet genom att förflytta den vertikala kanalen i anordningen. Vattenmodellexperiment har utförts för att validera simuleringsresultaten. Det kraftigt roterande flödet kunde endast beskrivas väl av Reynolds Stress Model (RSM). Validering utfördes också genom att mäta den radiella hastigheten i den vertikala kanalen med en Ultrasonic Velocity Profiler (UVP). TurboSwirl-anordningen vändes och kopplades till gjutröret för att generera det roterande flödet. Detta studerades både med numeriska modeller och med vattenmodellering. Ett periodiskt asymmetriskt roterande flöde observerades både i numeriska modellerna och i vattenmodellerna. För att modellera detta periodiska flöde så användes detached eddy simulation (DES) modellen. Resultaten då denna modell användes stämmer väl med de experimentella mätningarna. Denna nya design med TurboSwirl kan uppnå liknande styrka på det roterande flödet som när elektromagnetisk omrörning användes. Det resulterande roterande flödet leder till en lägre axiell hastighet i gjutröret samt en lugnare yta och ett lugnare flöde i kokillen. / <p>QC 20161123</p>

Computational Fluid Dynamics is a powerful and widely used tool for developing projectsthat concern flow motion, in very different fields. Industrial CFD solvers are continuouslydeveloped with the aim of improving accuracy and reducing the computational cost of thesimulations. Turbulent wall-flow cases are particular demanding as the presence of a solidsurfaceinterface generates steep gradients in the proximity of the wall. Resolving suchgradients can be crucial to obtain a consistent solution but also very expensive in terms ofgrid refinement, and hence computational time. Wall functions are widely used and offersignificant computational savings when it comes to near-wall flow resolution. Previous wallfunction implemented in the M-Edge solver suffered by poor performances in complex flowscharacterized by strong pressure-gradient phenomena, such as separation. A new formulationhas been developed and validated for k − omega and Spalart-Allmaras turbulence models. Testsimulations started from simple and near-ideal cases (2D zero pressure gradient flat plate)and advanced to always more complex flow cases and geometries (full 3D general fighter).Every case has been run coupling the wall-function boundary condition with three differentturbulence models: the Menter SST, the Menter BSL with an EARSM and the Spalart-Allmaras one-equation model. Overall results showed the upgraded performance of new wallfunction in flow resolution together with more agile grid requirements, faster and deeperconvergence of the residuals and a general reduction in computational time. / Berör strömmande fluider inom mycket olika områden. Industriella CFD-lösare utvecklaskontinuerligt i syfte att förbättra noggrannheten och minska beräkningskostnaderna försimuleringarna. Turbulent strömning nära väggar är särskilt krävande eftersom närvaron avett fast ytgränssnitt genererar stora gradienter i närheten av väggen. Att lösa upp sådanagradienter kan vara avgörande för att få en konsistent lösning men också mycket beräkningskrävandepå grund av nödvändig nätförfining.Väggfunktioner används ofta och ger betydandereduktioner i beräkningstid när det gäller att lösa upp strömningen nära vägg. En tidigareväggfunktion implementerad i M-Edge-lösaren led av dåliga prestanda i komplexa flödenmed starka tryckgradienter, såsom separation. En ny formulering har utvecklats och valideratsför k − omega och Spalart-Allmaras turbulensmodeller. Den har testats för enkla generiska fall(2D-plan platta utan tryckgradient) och för mer avancerade och komplexa strömningsfall ochgeometrier (komplett 3D-stridsflygplan).Varje fall har körts med väggfunktionens randvillkorkopplat med tre olika turbulensmodeller: Menter SST, Menter BSL med EARSM och Spalart-Allmaras enekvationsmodell. De övergripande resultaten visar att nya väggfunktionen gerbetydande förbättringar i att beskriva strömningen tillsammans med reducerade krav pånätupplösning, snabbare och djupare konvergens av lösningen och en allmän minskning avberäkningstiden.