2026-03-22
00:01 |
CFD Simulation methodology for stirred vessels validated by particle tracking velocimetry
Bílek, Vojtěch ; Gebouský, Ondřej ; Haidl, Jan ; Pivokonský, Martin
Stirred vessels are an integral part of many industrial processes. Their design is often based on only experimental data which are limited by available experimental techniques. Therefore, their optimisation is usually conducted via a trial-error approach. This study offers a validated CFD simulation methodology that could be used for optimisation and design of industrially relevant stirred vessels. The methodology is based on the RANS model employing the standard k − ϵ turbulence model and the multiple reference frame approach. The methodology is validated in a vessel that mimics the geometry of a flocculation tank, for which experimental data were also measured using particle tracking velocity and tracer tracking techniques. While the experimental and calculated flow fields show high agreement, simulations of tracer transport within the vessel indicate limitations in the standard approach to the turbulent transport modelling, specifically in the constant value of turbulent Schmidt number.
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2026-03-01
00:49 |
On flow simulation strategy for industrial mixed vessels
Haidl, Jan ; Bílek, Vojtěch ; Gebouský, Ondřej ; Pivokonský, Martin
The CFD-based analyses, optimizations, and troubleshooting of industrial-scale mixing tanks require a substantially simplified yet sufficiently accurate simulation strategy. Although there are numerous numerical studies on the simulation of various mixing vessels, most lack validation; based on a thorough review of studies reporting validated results, it is difficult to recommend a simulation methodology. This contribution summarizes a three-year effort to develop and validate such a recommended methodology. The methodology provides recommendations on mesh density, mesh structure, and the choice of turbulence model. The resulting strategy is first based on simulations of the flow field in a cylindrical baffled vessel, for which there is sufficient experimental data in the literature. Next, the strategy is validated using original experimental data obtained from a rectangular mixing tank with single- and double-impeller arrangements,\ntwo impeller types, and three impeller speeds.
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2026-03-01
00:49 |
Methodology for velocity field measurements in pilot-scale stirred vessels using 2-D particle tracking velocimetry
Gebouský, Ondřej ; Bílek, Vojtěch ; Haidl, Jan
Reliable validation of computational fluid dynamics (CFD) simulations of mixing in pilot- and industrialscale vessels is hindered by the scarcity of experimental data, particularly for non-standard geometries and operating conditions. To address this gap, a large-scale Particle Tracking Velocimetry (PTV) measurement methodology was developed, implemented, and critically evaluated. The methodology was applied to a pilot-scale rectangular stirred vessel operated in four configurations, comprising single- and dual-impeller arrangements with either Rushton turbines or pitched blade turbines. The contribution presents a comprehensive description of the experimental setup, including illumination, image acquisition, and seeding strategy, as well as the data processing workflow. Particular attention is given to trajectory reconstruction, validation criteria, and filtering procedures used to remove spurious or physically inconsistent particle trajectories. The resulting velocity and turbulent kinetic energy fields are analyzed with emphasis on their applicability for the validation of Reynolds-Averaged Navier–Stokes simulations. The advantages and limitations of the proposed PTV approach are critically discussed. While the methodology enables spatially resolved velocity measurements over large volumes and captures key flow structures, several shortcomings are identified. These include reduced accuracy of velocity estimates in high-speed regions near impeller discharge, limited reliability of turbulent kinetic energy estimation, and particle settling effects in low-velocity zones. Overall, the study provides practical guidance on the capabilities and limitations of large-scale PTV measurements and offers valuable experimental insights for validating CFD models of mixing in complex, industrially relevant vessels.
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2026-03-01
00:49 |
CFD simulation methodology validated for mixed rectangular tank equipped with single and multiple impellers
Bílek, Vojtěch ; Gebouský, Ondřej ; Haidl, Jan
An experimentally validated methodology for practical fluid dynamics modeling of vessels with atypical geometry, which differs from the standard cylindrical baffled vessel with a centrally mounted impeller, is absent. One reason for this is the lack of experimental data measured on such vessels. We measured experimental data for a rectangular tank equipped with a single impeller and a pair of impellers; either Rushton turbines or pitched-blade turbines (mimicking the geometry of the flocculation tanks at water treatment facilities)-using the particle tracking velocimetry (PTV) technique, as presented in the si- multaneously published contribution. Accordingly, this study exploits the measured data to extend the range of operational conditions under which the previously proposed methodology has been validated by systematically comparing experimental measurements with simulation results and providing a critical evaluation of their agreement and limitations. The study identified specific limitations of the proposed simulation methodology when applied to flows characterized by strong impeller–impeller interactions and introduced an extension to the methodology that addresses these deficiencies. The resulting approach is suitable for the analysis and numerical simulation of realistic fluid dynamics in stirred apparatuses exhibiting complex flow structures.
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2026-02-01
00:15 |
Založení hydrologického monitoringu vybraných krkonošských rašelinišť
Vlček, Lukáš ; Šípek, Václav ; Zelíková, Nikol
Zpráva shrnuje výsledky založení hydrologického monitoringu dvou vybraných krkonošských rašelinišť (Jakšín a Kyselé Kouty) v letech 2023–2024. Hodnocena je dynamika hladiny podzemní vody, teplotní režim půdy a chemické složení vody s cílem posoudit zdroje vodnosti, retenční schopnosti v kontextu změn srážkového režimu. Výsledky slouží jako podklad pro vyhodnocení účinnosti revitalizačních opatření a pro další fáze ochrany a obnovy mokřadních ekosystémů v Krkonošském národním parku.
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2026-01-24
00:12 |
Adaptation of agricultural systems to climate change in the Reqame watershed, Halaba and Silte areas
Vlček, Lukáš ; Šípek, Václav
The report evaluates hydro-pedological processes and erosion dynamics in the Halaba and Silte areas, Ethiopia, with the aim of supporting climate-change adaptation in agricultural systems. Field monitoring of precipitation, soil moisture, and discharge was combined with detailed soil profile characterization, laboratory analysis of hydraulic properties, and hydrological modelling using HEC-HMS. Results indicate generally low infiltration capacities, rapid surface runoff generation, and strong contrasts in stability and erodibility between soil horizons. Scenario-based modelling demonstrates that the effectiveness of soil and water conservation measures strongly depends on slope position, soil condition, and structure design. The study provides technically grounded recommendations for the targeted application of retention and drainage structures to reduce erosion risk and enhance sustainable land management under increasing rainfall variability.\nThe study is the result of the project ‚Adaptation of agricultural systems to climate change in the Reqame watershed, Halaba, and Silte areas’ granted by Czech AID.
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2026-01-24
00:12 |
Výskyt germania, arsenu a antimonu ve vodních nádržích Vrchlice a Souš
Prokopová, Michaela ; Sichrová, Kateřina ; Čermáková, Lenka ; Matoušek, Tomáš ; Filella, M. ; Pivokonský, Martin
Souhrnná výzkumná zpráva podrobně vysvětluje problematiku výskytu jednotlivých specií arsenu, antimonu a germania ve vodních nádržích Vrchlice a Souš, jejich vzájemné přeměny v závislosti na ročním cyklu, a to ve vztahu ke geologicko-biologickým poměrům ve vodních ekosystémech.
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2025-12-16
16:40 |
Co lze vyčíst z dynamiky hladiny podzemní vody v rašeliništích?
Vlček, Lukáš ; Kocum, Jiří
Práce se zabývá dynamikou hladiny podzemní vody v rašeliništích a zdůrazňuje, že jediná úroveň měřené hladiny nedokáže postihnout složité hydrologické procesy v těchto ekosystémech. Vysvětluje rozdíly mezi reakcí akrotelmu a katotelmu, význam hloubky a perforace vrtů i roli podloží v pohybové dynamice vody. Ukazuje, že kombinace více vrtů různé hloubky umožňuje určit směry proudění, identifikovat vliv klimatu a podzemní vody a přesněji hodnotit stav a zranitelnost rašelinišť. Závěry podtrhují nutnost komplexního monitoringu pro správnou interpretaci hydrologického režimu.
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2025-12-16
16:40 |
Response of dissolved organic carbon to rainfall-runoff events in streams draining peatbogs
Matoušková, M. ; Fraindová, K. ; Bejčková, M. ; Kliment, Z. ; Vlach, V. ; Vlček, Lukáš
The presented study investigates the dynamics of DOC concentrations in headwater peatbog areas with respect to the extreme rainfall-runoff (R-R) events hydrometeorological catchment preconditions. The main data sources were automatic devices for monitoring of groundwater level, discharges and rainfalls installed in the Vydra River catchment and one automatic water sampler ISCO in sub-catchment of the Rokytka River basin in the Šumava National Park. Changes in groundwater level and discharges had the greatest influence on DOC concentrations. Higher mean and maximum DOC were measured during events after a longer period without an extreme R-R event. The greater lag time of maximum DOC after peak flow and the higher mean DOC during the event were primarily due to hydrometeorological preconditions of the catchment. The highest DOC was in autumn after previous summer period with low discharges and low groundwater level. DOC was also positively corelated with air and water temperatures.
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2025-12-16
16:40 |
Transpirace buku a smrku: propojení měření mízního toku a stabilních izotopů
Pátek, Karel ; Šípek, Václav ; Kocum, Jiří ; Vlček, Lukáš ; Bouda, Martin ; Tesař, Miroslav
Transpirace stromů, jako významná složka vodní bilance, byla zkoumána za pomoci dvou různých přístupů. Prvním bylo měření mízního toku, které umožnilo porovnat množství vody spotřebované buky a smrky. Druhým přístupem bylo sledování izotopového složení mízy ve stromech, které ukázalo, jestli stromy používaly vodu pocházející ze zimních nebo letních srážek. Získané poznatky o chování buků a smrků jsou důležité nejen pro popis současné vodní bilance, ale umožní také předpovědět očekávané důsledky klimatické změny spojené s nárůstem teplot nebo přeměnou druhového složení lesů.
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