see document / This report describes an international effort to investigate the present limitations of some of the commercially available CFD codes and their models. This investigation involves comparing the predictions from these codes with the experimental results of the two selected test cases. The data collection method is briefly described followed by a detailed discussion of the graphical approach used by the group of investigators to compare results. In addition, an attempt to investigate the deviation of the collected results with the experimental data is discussed. / Master of Science

<div>A numerical simulation was developed to capture the phenomena of electromagnetic stirring in a metallurgical ladle. Electromagnetic stirring requires an external magnetic field to be imposed on the molten steel bath, which is governed by the principles of magnetohydrodynamics. Electromagnetic stirring benefits over traditional stirring methods by offering non-invasive stirring, melt homogeneity, and ease of configuration alterations. Insight to the electromagnetic stirring phenomena is limited experimentally due to the high temperatures of the molten-steel bath. This investigation will include two numerical simulations, the first of which is to generate a magnetic field to properly stir the steel bath. The second incorporates the generated magnetic field and solves the fluid flow due to the magnetohydrodynamics interactions. The results of these numerical simulations will help to provide further understanding of the electromagnetic stirring method. This simulation was used to analyze the molten-steel bulk velocity, vortex formation, flow development time, slag-eye size, and wall shear stress in a metallurgical ladle.</div><div><br></div><div><div>The transient development of the bulk velocity in an EMS ladle was compared with the literature study completed by Sand et al. 2009. The comparison of the developed bulk velocity resulted in a percentage difference of 0.98% and an absolute difference of 0.007 [m/s]. Both numerical models, in the current work and the literature study, obtained a developed flow within 25 seconds of stirring. For the parametric studies, it was found that the addition of a circumferential taper angle to the geometry reduced the bulk velocity and slag-eye size formed compared to a cylindrical ladle. The electric current amperage of the external magnetic field coil system was determined to precisely adjust the bulk velocity. A 150 [A] reduction in amperage results in a ~20% loss in the bulk velocity magnitude. The locations of the high shear stress regions were determined which remained near the stirring unit.</div><div><br></div><div>From this study, it is recommended to use a magnetohydrodynamics package offered within a multiphysics numerical solver since the FLUENT® MHD module inherently under-predicts the velocity as well as the issue of the numerical instabilities of the Lorentz force calculations.</div></div><div><br></div>

The triboelectrification of particles by contact or frictional charging is known to be an operational challenge in the polyolefin industry. Particularly in polyethylene production, gas-solid fluidized bed reactors are known to be susceptible to electrostatic charging due to the rigorous mixing of polyethylene and catalyst particles in a dry environment. The presence of charged particles coupled with a highly exothermic polymerization reaction results in sheet formation on the reactor walls. This behaviour can decrease reactor performance and obstruct the system, consequently forcing a shutdown for reactor maintenance. The generation of electrostatic charge in fluidized beds has been widely studied throughout the years; however, limited attention has been paid to the simulation and modeling of this phenomenon. Since it is difficult to accurately quantify the charge generation in industrial fluidized beds, developing an electrostatic model based on material properties would considerably aid in providing insight on this occurrence and its effects. A computational fluid dynamics (CFD) model that incorporates this electrostatic model can then be used as a predictive tool in research and development. Simulating electrostatic charging in gas-solid fluidized beds would be a cost-effective alternative to running experiments on them, especially for industrial-scale test runs. In this thesis, an electrostatic charging model was developed to be used in conjunction with an Euler-Euler Two-Fluid CFD model to simulate triboelectrification and its effects in gas-solid flows. The electrostatic model was first established for mono-dispersed gas-particle flows and was validated using past experimental findings of particle charging for gas-solid fluidization runs. With the goal of providing a realistic representation of gas-solid fluidization of polyethylene resins with a wide particle-size distribution, the electrostatic model was extended to consider bi-dispersed particulate flow systems. Simulation results using this model show the prediction of bipolar charging when the particles have different sizes, even though they are made of the same material. This phenomenon is analyzed and is shown to be driven by the electric field produced by the charge accumulated on the particles. Experimental studies of particle-wall and particle-particle contact charging were performed to investigate the electrostatic and mechanical parameters that are crucial for modeling the magnitude and direction of charge transfer in gas-solid flow systems. Particle-wall contact charging due to single and repeated collisions were tested with various particles, including commercial linear low-density polyethylene, to determine their rates of charging as well as their charge saturation limits when colliding with a metal surface. Plotting the charge saturation value of the particles against their respective surface areas revealed a linear trend which could be used to calculate the charge saturation of the particle for a given particle size. Additional particle-wall charging studies include the effect of initial charge, collision frequency, particle type, impact angle, impact velocity and the presence of impurities on particle charging. To study particle-particle contact charging, a novel apparatus was designed, built, and tested to determine the magnitude and direction of charge transfer due to the individual particle-particle collisions of insulator particles. This apparatus was the first of its kind, and it ensured that the measured charge transfer for each experimental trial was solely due to the binary collision between the particles. It was observed that the direction of charge transfer in identical particle collisions is not dictated by the net initial charges of the particles, but the localized charge difference at the particles’ contacting surface. Moreover, particle-particle collisions of nylon particles of varying sizes confirmed the bipolar charging phenomena, where the direction of charging was dictated by the relative size of the colliding particles. These findings, among others, contradict the charge transfer behavior predicted by electrostatic charging models currently proposed for particle-particle collisions. As such, it was concluded that an empirically accurate charge transfer model needs to be established to simulate the electrostatic charging of particles in poly-dispersed gas-solid flow systems.

In this thesis, the different solution methods for saddle-point systems aris- ing from fluid dynamics are studied. The main emphasis is on Krylov subspace methods with effective preconditioning techniques for saddle-point systems ob- tained from finite element discretization of the Navier-Stokes equations. Two preconditioning techniques are presented: pressure-convection-diffusion precon- ditioning (PCD) and least-square commutator preconditioning (LSC). Both pre- conditioners are validated on two benchmarks: lid-driven cavity and flow around cylinder. From the computational point of view, we focus on comparing the performance of used solvers, with emphasis on our implementation of PCD pre- conditioning. All numerical simulations are performed by software Firedrake. 1

Three-dimensional urban wind field construction plays an important role not only in the analysis of pedestrian levels of comfort but also in the effectiveness of harnessing wind energy in an urban environment. However, it is challenging to accurately simulate urban wind flow due to the complex land use in urban environments. In this study, a three-dimensional numerical model was developed for urban wind flow construction. To obtain an accurate urban wind field, various turbulence models, including the Reynolds Stress Model (RSM), Shear-Stress Transport (SST) k-ω, realizable k-ε, and Re-Normalization Group (RNG) k-ε models were tested. Simulation results were compared with experimental data in the literature. The RSM model showed promising potential in simulating urban wind flow. The model was then adopted to simulate urban wind flow for Purdue University Northwest, which is located in the Northwest Indiana urban region. Based on the simulation results, the optimal location was identified for urban wind turbine siting and the wind comfort was analyzed in the walk sides between the buildings.

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Ambulance hall is a significant station during emergency treatment. Patients need to be transferred from ambulance cars to the hospital’s building in the hall. Eligible performance of ventilation system to supply satisfied thermal comfort and healthy indoor air quality is very important. Computational fluid dynamic (CFD) simulation as a broadly applied technology for predicting fluid flow distribution has been implemented in this project. There has two objectives for the project. The first objective is to make comparison between the three CFD software which consists of ANSYS Fluent, Star-CCM+ and IESVE Mcroflo according to CFD modeling of the baseline model. And the second objective is to build CFD modeling for cases with difference boundary conditions to verify the designed ventilation system performance of the ambulance hall. In terms of simulation results from the three baseline models, ANSYS Fluent is conclusively recommended for CFD modeling of complicated indoor fluid environment compared with Star-CCM+ and IESVE Microflo. Regarding to the second objective, simulation results of case 2 and case 3 have shown the designed ventilation system for the ambulance hall satisfied thermal comfort level which regulated by ASHRAE standard with closed gates. Nevertheless, threshold limit value of the contaminants concentration which regulated by ASHRAE IAQ Standard cannot be achieved. From simulation results of case 4.1 to 4.3 shown that the designed ventilation system cannot satisfy indoor thermal comfort level when the gates of the ambulance hall opened in winter. In conclusion, measures for decreasing contaminants concentration and increasing indoor air temperature demanded to be considered in further design.

With the increase in length of wind turbine blades flutter is becoming a potential design constrain, hence the interest in computational tools for fluid-structure interaction studies. The general approach to this problem makes use of simplified aerodynamic computational tools. Scope of this work is to investigate the outcomes of a 3D CFD simulation of a complete wind turbine blade, both in terms of numerical results and computational cost. The model studied is a 5MW theoretical wind turbine from NREL. The simulation was performed with ANSYS-CFX, with different volume mesh and turbulence model, in steady-state and transient mode. The convergence history and computational time was analyzed, and the pressure distribution was compared to a high fidelity numerical result of the same blade. All the model studied were about two orders of magnitude lighter than the reference in computation time, while showing comparable results in most of the cases. The results were affected more by turbulence model than mesh density, and some turbulence models did not converge to a solution. In general seems possible to obtain good results from a complete 3D CFD simulation while keeping the computational cost reasonably low. Attention should be paid to mesh quality.

The understanding of secondary flow behavior has become an important aspect in the design of modern gas turbines. Secondary flow gives rise to aerodynamic losses, distorts the thermal field and affects the flow conditions at the exit of a passage negatively. Therefore, reducing secondary flow is a major concern for efficiency improvement. Many passive control-methods have been suggested by turbine designers and researchers, and one very promising modification is blade leading edge contouring near the endwall. At the Division of Heat and Power Technology KTH, Stockholm, a detailed experimental investigation of three filleted nozzle guide vanes in an annular sector cascade has been performed, providing excellent experimental data for numerical validation of complex turbine flows. Based on the above, a numerical study and aerodynamic investigation for a leading edge filleted vane and baseline vane has been performed. The potential effect of the leading edge fillet on flow structure and secondary losses has been evaluated based on a number of flow parameters, and computational predictions have been compared to experimental results. The numerical investigation has shown some differences in the flow behavior between the filleted and baseline case. All results indicate that the fillet affects the flow structure in regions close to the hub endwall. It shifts the position of vortices and loss core. However, the overall effect on reducing secondary losses downstream of the passage is insignificant. Additionally, the numerical results show good qualitative agreement with experimental results.

År 2004 infördes EU:s ramdirektiv för vatten i svensk lagstiftning vilket har inneburit att vattendragets funktion som vandringsväg för fisk behöver upprätthållas eller säkras, även efter att dammar byggts. För vattenkraftverksdammar kan detta ske genom att dammarna rivs eller förses med olika typer av anordningar för passage upp- och nedströms dammen. Vid Sikfors vattenkraftverk finns en ledarm för att leda smolten till ett utskov för passage nedströms dammen. Studier har dock visat att smolten dör i för stor utsträckning vid passage via utskovet, och projektets syfte har därför varit att ta fram en modell för flödet över utskovet. Modellen har ställts upp för tre volymflöden, 18, 30 och 59 m3/s och vattendjup, vattenhastighet och flödesbeteende har analyserats för volymflödena.  Geometrin en bit uppströms dammen, luckan och skibordet byggdes upp i Designmodeler utifrån ritningar. För att underlätta simuleringarna delades geometrin i två delar, där den första delen innefattar geometrin en bit uppströms dammen samt luckan medan den andra geometrin innefattar skibord och uppkastare och nedslagsplats. Simuleringen gjordes i ANSYS CFX och vattenytan modellerades som en fri yta med luft och vatten som fluider i modellen. Luckans öppning varierades med volymflödet, utifrån data från vattenkraftverket.  Det lägsta vattendjupet över luckan blev 5 cm vid slutet av luckan för ett volymflöde på 18 m3/s, medan för 30 m3/s blev det lägsta vattendjupet 10 cm vid slutet av luckan. Den högsta vattenhastigheten över luckan blev 8,5 m/s för 30 m3/s i mitten av luckan medan samma hastighet blev 8,3 och 8,9 m/s för volymflöde på 18 respektive 59 m3/s.  För skibordet blev det lägsta vattendjupet 15 cm och 30 cm för 18 respektive 30 m3/s. Vattenhastigheten för samtliga volymflöden för skibordet överstiger 12 m/s, vilket är den högsta rekommenderade hastigheten för nedströmspassage. För 30 och 59 m3/s kastas vattnet över ingången till fisktrappan, medan för 18 m3/s påverkas flödet vid ingången utav flödet från utskovet. Vattendjupet för 30 m3/s borde vara tillräckligt för att smolten inte ska få skrapskador, medan 18 m3/s kan vara för lågt volymflöde. Ingen tendens för virvlar eller turbulens syns för luckan eller skibordet för något volymflöde, så flödesbeteendet borde inte vara ett problem för smolten. Vattenhastigheten för skibordet överskrider den högsta rekommenderade hastigheten, men hastigheten är inte mycket högre än rekommenderat och under en kort period, så det borde inte vara den enskilda orsaken till smoltens låga överlevnadsgrad.    Den numeriska modellen har ställts upp för tre volymflöden, och kontrollerats mot teoretiska beräkningar och mot parametrar för meshkvalitet, som visar att modellen är bra uppställd. Analysen har visat att vattendjup och vattenhastighet är beroende av volymflödet över utskovet, och att skillnaden är större för vattendjupet. Flödesbeteendet visar ingen tendens till turbulens eller virvlar, och flödesbeteendet följer ett typiskt beteende för kanalströmning.