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Validation of Selected Software in Terms of Air Age Simulation
Kučírek, Pavel ; Šikula, Ondřej
The paper pertains to the assessment of indoor air quality in terms of its air age in a ventilated space. It involves a comparison of Computational Fluid Dynamics (hereinafter CFD) simulation software and their validation by an experiment carried out in a test chamber. A total of 14 cases were simulated and compared using the software: OpenFOAM, Blue CFD-AIR, DesignBuilder, and Ansys. The aim is to evaluate the accuracy and usability of the software by comparing selected computational domains and meshes. The results obtained show that the assessed software achieves satisfactory accuracy for air velocities and air ages. Models with simplified inlet geometry and half-domain offer the best balance between accuracy and computational effort.
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Flow simulations approach for flocculation tanks
Idžakovičová, Kristýna ; Bílek, Vojtěch ; Haidl, Jan ; Isoz, M. ; Pivokonský, Martin
Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and savings of operational costs. However, it is currently based on trial-and-error experimental approaches. In this contribution, we focus on flow modeling in stirred flocculation tanks that would, after coupling with a calibrated model of particle aggregation, enable simulationbased flocculation optimization. Despite the abundance of literature on stirred tank modeling, there is no universal agreement on the methodology used to describe turbulence nor on the approach to the computational mesh creation. Consequently, there is no unified methodology for simulations and their validation. To address this, we present a best-practice methodology for economical, yet reliable flow simulations in the said device. This methodology includes the choice of the turbulence model, the approach to the design of a high quality mesh suitable for arbitrary geometries, and results evaluation. It is developed based on an extensive literature review, a multitude of flow simulations using several meshes of progressively higher quality and resolution, and various strategies to converge to steady-state flow conditions. The simulation quality indicators used here involve comparison with the experimental data on fluid velocity, stirrer power output, and flow rate through the impeller zone. Additionally, the resulting flow simulation models are compared using tracer transport simulations, hinting at their potential for coupling with particle aggregation models.
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Flow simulations approach for flocculation tanks
Idžakovičová, Kristýna ; Bílek, V. ; Haidl, J. ; Isoz, Martin ; Pivokonský, M.
Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and savings of operational costs. However, it is currently based on trial-and-error experimental approaches. In this contribution, we focus on flow modeling in stirred flocculation tanks that would, after coupling with a calibrated model of particle aggregation, enable simulationbased flocculation optimization. Despite the abundance of literature on stirred tank modeling, there is no universal agreement on the methodology used to describe turbulence nor on the approach to the computational mesh creation. Consequently, there is no unified methodology for simulations and their validation. To address this, we present a best-practice methodology for economical, yet reliable flow simulations in the said device. This methodology includes the choice of the turbulence model, the approach to the design of a high quality mesh suitable for arbitrary geometries, and results evaluation. It is developed based on an extensive literature review, a multitude of flow simulations using several meshes of progressively higher quality and resolution, and various strategies to converge to steady-state flow conditions. The simulation quality indicators used here involve comparison with the experimental data on fluid velocity, stirrer power output, and flow rate through the impeller zone. Additionally, the resulting flow simulation models are compared using tracer transport simulations, hinting at their potential for coupling with particle aggregation models.
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Study of the Dissipation in Spiraling Vortical Structures
Štefan, David ; Drábková, Sylva (referee) ; Koutník,, Jiří (referee) ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
This work deals with study of swirling flows where the spiral vortical structure appears. The main relation is to flow seen in the draft tube cone of hydraulic turbines operated out of the design point (i.e. best efficiency point). In this cases large coherent vortex structure (vortex rope) appears and consequently high pressure pulsations are propagated to the whole machine system leading to possible restriction of turbine operation. This flow features are consequence of flow instability called vortex breakdown in case of Francis turbine operated at part load (flow rate lower than optimal one). The present study is carried out using simplified device of swirl generator in order to access similar flow conditions as can be found in real hydraulic turbines. Both the dynamic and dissipation effect of spiral vortex breakdown are investigated. The first part of thesis deals with spiral form of vortex breakdown. The experimentally measured velocity profiles (LDA) and wall static pressures are correlated with numerical simulations carried out using open-source CFD package OpenFOAM 2.2.2. The high speed camera recording of cavitating vortex core is used to obtain image ensemble for further post-processing. The dissipation effect of spiral vortex structure is in detail discussed based on computed flow fields. The second part of thesis is dedicated to the application of POD decomposition to the study of spatio-temporal features of spiral vortex dynamics. Firstly the POD is applied to the both the experimentally obtained image ensemble of cavitating vortex and numerically computed static pressure fields. Secondly the comprehensive analysis of spiral vortex mitigation effect by the axial water jet is analyzed. The collaborative study employing the swirl generator apparatus designed by the researchers from Politehnica University of Timisoara in Romania is performed and changes in spatio-temporal vortex dynamic are studied. In this study the numerical data (in a form of three-dimensional pressure and velocity fields) are obtained using commercial CFD software ANSYS Fluent R14.
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2-D external aerodynamics of an unusual shaped body
Mohyla, Daniel ; Gal, Pavel (referee) ; Dohnal, Miloslav (advisor)
This bachelor thesis is focused on analysis of flow over a cylindrical rod in 2-D space by using computational fluid dynamics (CFD) with turbulence models k- SST and k- SSTSAS. First part of this thesis is meant to be an introduction to the topic of extrernal flow and CFD. In this part the topics of flow separation, turblence modeling and various related models are discussed. Second part deals with the description of simulation case inside of open source CFD software called OpenFOAM and the obtained results. In last part the disccusion about results is carried out and results are compared.
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Parametric Generator of Heat Exchanger Tube Bundle Mesh for OpenFOAM
Petrů, Martin ; Juřena, Tomáš (referee) ; Turek, Vojtěch (advisor)
This thesis deals with the basics of computational fluid dynamics (CFD), the reasons for its use, and the related necessity to create computational meshes. The next part of the thesis focuses on assessing the quality of computational meshes and, briefly, on computational methods of CFD. The available mesh generators are also compared, and an overview of meshing capabilities is provided. The following is basic information about the OpenFOAM software and its capabilities, in particular the creation of meshes using the blockMesh application. The following part of the thesis is focused on the description of the developed application and its functions for generating a high-quality computing mesh of a tube bundle heat exchanger for the OpenFOAM software. In conclusion, a steady flow simulation verifies the correctness of the created mesh and its sufficient quality.
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Preliminary aerodynamic analysis of remotely controlled model with jet propulsion
Novák, Ondřej ; Zikmund, Pavel (referee) ; Popela, Robert (advisor)
This bachelor´s thesis deals with aerodynamic analysis of unmanned aircraft and subsequent changes to design of wing, its position and wing-fuselage junction. In this work emphasis is laid on flow separation, its interaction with other flow structures and its influence on aerodynamic properties. The goal of these changes to the aircraft is ensuring sufficient stability and controllability in low as well as high angle of attack flight. AVL, XFLR5 and CFD methods were used in the thesis. In case of inaccuracy of CFD calculation, two backup wing related modifications were prepared.
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Sports car rear wing numerical optimization
Feldová, Petra ; Rudolf, Pavel (referee) ; Štefan, David (advisor)
This master’s thesis is focused on optimization of rear wing of sport car by using open-source software. The optimization of 2D profile of the rear wing is present in this thesis. Python environment was chosen for optimization and evolutionary algorithm was is used as optimization function. This algorithm is further connected to Xfoil software, which is computing aerodynamic characteristic. The ratio of the lift and drag coefficients (C_L/C_D) is chosen as parameter which considers the aerodynamic efficiency. The CFD computation of flowing around the whole car is provided in open-source software OpenFOAM. . The profile optimization results to approximately 7.9 % raise of the parameter C_L/C_D, in the same wing stability. The main benefit of this work is to use open-source software for the optimization and CFD analysis, which in future might save company’s resources by not buying expensive commercial software licenses.
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Intake vortex modeling
Galuška, Jiří ; Kozák, Jiří (referee) ; Rudolf, Pavel (advisor)
This paper covers information research of basic design rules of industrial wet sumps. It describes mathematical models of vortices and method for their identification and visualization. Then the author focuses on CFD modeling of surface vortices with single phase and multiphase approach with Volume of Fluid method. Basic principles of multiphase CFD modelling in OpenFOAM and ANSYS Fluent are given. Description and benchmarking of suitable turbulence models is also present. The single phase and multiphase approach were successfully validated for a simple test case of bathtub surface vortex. Satisfactory agreement with experimental data was achieved. The accuracy and behavior of both solvers were compared between each other. This gives us useful tool for evaluation of inflow condition and danger of surface vortex occurrence in wet sumps. The acquired knowledges were used to design an experimental test case with geometry similar to industrial wet sump. A map of surface vortex occurrence has been created for different operating points. One of the operating point has been used for numerical simulation (both single phase and multiphase). Partial agreement with experimental observation has been achieved.
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