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Item PIV measurement of wakes past stator wheel inside air test turbine VT-400 in two axial×tangential planes(Brno University of Technology, Institute of Solid Mechanics, Mechatronics and Biomechanics, 2024) Duda, Daniel; Uruba, Václav; Yanovych, Vitalii; Klimko, Marek; Tomášková, Tetjana; Jeřábek, Matěj; Žitek, Pavel; Milčák, PetrVT-400 is a single-stage test turbine working with ambient air located at the University of West Bohemia in Pilsen. Inside this turbine, we perform a PIV (Particle Image Velocimetry) measurement of the flow field in two planes oriented in axial × tangential direction. There planes are located between the stator wheel and rotor wheel; first one is near the hub, second one at the middle of blade height. The spatial distribution of velocity fluctuations displays system of wakes and jets oriented diagonally over the studied area. The jets are represented by higher mean velocity and lower turbulence, the wakes oppositely. The spatial size of fluctuations is analyzed in terms of autocorrelation function: the size of correlated region is comparable with the wake width, additionally, there is apparent a wave in the stream-wise direction. At different turbine working parameters, we observed at least two distinct wavelengths. The neighboring wakes do not interact in the limits of studied areas.
Item PIV measurement of near shear layer of a circular jet(EPJ Web of Conferences, 2024) Duda, Daniel; Yanovych, Vitalii; Tsymbalyuk, Volodymyr; Uruba, VáclavThe shear layer (SL) of a turbulent jet is studied by using Particle Image Velocimetry (PIV) up to distance 0.2 nozzle diameters in axial × radial plane. The jet is generated by circular nozzle at Reynolds numbers 1.1·105 to 1.1·106. This range covers the transition from laminar instable SL to turbulent SL. The observed average velocity profiles are fitted by using Michalke function. This function describes both: the shear layer of tanh profile and the boundary layer formed inside the nozzle at the same time. In the second part of this contribution we show the fluctuations, their anisotropy and length-scale observing doubling in the wavelength at the transition.Item Turbulence organization in isolated roughness flow(MATEC Web of Conferences, 2023) Yanovych, Vitalii; Duda, Daniel; Uruba, VáclavThe primary goal of this investigation was to analyze the specific evolution of the boundary layer over an isolated roughness. A specific surface consisting of rectangular elements of the same height arranged in a checkerboard pattern was used for the experiments. Throughout the experiment, the measuring cross-sections were positioned at various distances from the inlet, while maintaining a constant flow velocity of 15 m·s-1. To investigate the boundary layer topology in the streamwise directions, a 55P14 miniature hot-wire probe was employed. It is worth mentioning that the measuring position was situated at the midpoint between the roughness elements. Through the analysis of the gathered data, we identified the distribution patterns of the mean velocity profile at different measuring positions. Additionally, we estimated the integral scale of the turbulence by applying different approaches, such as the zero-crossing method (based on autocorrelation analysis), and the Roach and Karman methods (based on spectral density function). The data obtained from our experiments demonstrate that the presence of isolated roughness leads to a pronounced alteration of the velocity profile. This phenomenon is likely due to the shear layer, which typically contains the largest and most energetic vortices in the flow.Item Roughness density effect on turbulent boundary layer evolution(EPJ Web of Conferences, 2024) Yanovych, Vitalii; Sokolenko, Vasyl; Uruba, Václav; Duda, DanielThis work aimed to investigate the boundary layer topology over various densities of roughness. For experiments, we used three different surface conditions comprised of rectangular elements with uniform height arranged in staggered rows and covered the entire floor of the wind tunnel. The frontal and plan solidity for each case changed, λf from 0.3 to 1.2 and λp from 1.3 to 4.7, respectively. Also, we used one more surface, without roughness, for comparison. During the experiment, the position of measuring cross-sections varied relative to the inlet, while the free flow velocity was 5 m·s-1. Thus, the corresponding Reynolds number Reτ was from 300 to 1500 (based on boundary layer thickness δ and friction velocity uτ) or Reθ was from 400 to 5500 (based on momentum thickness). To determine the boundary layer topology in streamwise directions, we used a 55P14 miniature hot-wire probe. The obtained data allowed us to estimate patterns of distribution mean velocity profile, streamwise Reynolds stress, and turbulence intensity for different surface cases. In addition, an analysis of the scales of the turbulent flow over different surface types was also carried out. Namely, the integral length scale, Taylor microscale, and dissipation scale were determined. Obtained results show that roughness density composition strongly affects boundary layer characteristics. The obtained results also represent a correlation between the Taylor microscale and the initial position of the log region.Item Enhanced Flutter Test Rig for a Transonic Flow in a Linear Turbine Blade Cascade and Numerical Data Validation(ETC, 2023) Tsymbalyuk, Volodymyr; Eret, Petr; Sláma, Václav; Rudas, Bartoloměj; Macálka, Aleš; Peterka, Tomáš; Ira, JiříModern efficient and robust steam turbines must be designed for large operating ranges and run at off-design conditions and high backpressures. Therefore, there is a danger that in some operating conditions, last-stage rotor blades can suffer from self-excited vibration (flutter), leading to severe failures of rotor blades or turbine units. In order to avoid this, the design of aerodynamically stable last stage rotor blades became a major topic for all steam turbine manufacturers and a validated numerical model for flutter prediction during the blade preliminary design phase is required. As flutter measurement is impossible in real turbines, controlled flutter tests on simplified experimental models must be used. However, experimental flutter testing facilities are rare. This paper reports on a flutter test rig enhancement to transonic flow and numerical data validation of aerodynamic stability in a linear turbine blade cascade. Aerodynamic forces and moments are estimated for different boundary conditions at pure bending, pure torsion and combined modes. The results are compared to numerical simulations performed using commercial code ANSYS CFX. Good agreement between the experiment and the numerical simulations proved a successful validation of the numerical tool.Item Development of a Digital Twin of an Oil-Flooded Screw Compressor Using Measurement Data and Numerical Simulations(Springer, 2024) Richter, Lukáš; Volf, Michal; Jeřábek, Matěj; Novotný, Zdeněk; Salajka, PetrThe paper describes the development of a digital twin of an industrial compressor with an integrated compressed air adsorption dryer. Digital twin development is enabled by prototyping an oil-flooded screw compressor with an integrated dryer and numerical modelling of partial phenomena and the whole system. The results of the numerical modelling and measurements of the prototype are then used to train and adapt neural networks to develop the digital twin software. A sufficient amount of input data is essential for the development and subsequent application of the digital twin of the compressor including the integrated dryer. These data must correspond to both standard operating conditions and off-design conditions with respect to, for example, ambient temperature, intake air humidity, compressor load or regeneration air temperature and quantity, which are taken into account in the measurements and numerical simulations. Taking into account the different operating conditions allows the neural networks to find the optimal design parameters for the entire compressor station with respect to the specific requirements and conditions of the end users, which is an important aspect of the added value of the digital twin.
Item Subsonic stall flutter of a linear turbine blade cascade using experimental and CFD analysis(ASME, 2020) Slama, Vaclav; Rudas, Bartolomej; Ira, Jiri; Macalka, Ales; Eret, Petr; Tsymbalyuk, VolodymyrStall flutter of long blades influences the operation safety of the large steam turbines in off-design conditions. As angles of attack are typically high, a partial or complete separation of the flow from the blade surface occurs. The prediction of stall flutter of turbine blades is a crucial task in the design and development of modern turbomachinery units and reliable design tools are necessary. In this work, aerodynamic stability of a linear turbine blade cascade is tested experimentally at high angle of attack +15°, Ma = 0.2 and the reduced frequency of 0.38. Controlled flutter testing has been performed in a travelling wave mode approach for the torsion with the motion amplitude of 0.5°. In addition, ANSYS CFX with SST k-ω turbulent model is used for URANS simulations of a full-scale computational domain. A separation bubble formed on suction surface near the leading edge has been found in CFD results for each blade. Excellent agreement between the experimental and numerical results in stability maps has been achieved for this case under investigation. This is encouraging and both experimental and numerical techniques will be tested further.Item Cooling of Steam Turbine Exhaust Hood and Last Stage Blade(EDP Sciences, 2023) Hoznedl, Michal; Ruml, Zdeněk; Vlasák, Jakub; Bém, Jindřich; Kubíková, Tereza; Ranš, MatějThis paper describes a novel semi-numerical method of water droplets path lines calculation in steam turbine axial exhaust hood 2D space. The axial velocity profile of steam as well as droplets evaporation are taken into account. Water droplets occur in several cooling nozzles placed on the outer wall of axial exhaust hood. Mathematical model of all water nozzles used in Doosan Škoda steam turbines was developed. Position and angle of cooling nozzles towards the outer exhaust hood wall influence the possibility of last stage blade trailing edges erosion given by droplets flow from the nozzles. The turbine lifetime is prolonged as the final consequence.Item Drag Estimation in the Near Wake of the NREL's Airfoils Based on Hot-Wire Data(EDP Sciences, 2022) Yanovych, Vitalii; Duda, Daniel; Uruba, Václav; Antoš, PavelThis paper presents the results of the drag coefficient estimations for different types of NREL airfoils based on the experimental data. Namely, it was S803, S807, S813, and S817 profiles with the same chord length. The investigations were conducted at three angles of attack α=0°, α=±5°, different chord-based Reynolds numbers 0.6×105, 1.3×105 and 2.6×105. While, measuring cross-sections were placed behind the trailing edge at x∙c−1≈0.2, 0.4 and 1.0. Experimental data were collected using a hot-wire split fiber probe 55R55, which allowed us to estimate the characteristics of turbulent flow in stream-wise and crosswise directions. According to the obtained results, the highest and lowest Cd values correspond to profiles S817 and S803, respectively. Moreover, the results show that more asymmetric profiles S803 and S807 have the lowest resistance at zero angles of attack.Research background: Application of Antonia and Rajagopalan methodology to drag assessment of various stream bodies.Purpose of the article: Comparative evaluation of the drag coefficients of the NREL airfoils based on instantaneous velocity distribution behind.Methods: Hot-wire anemometry with split fiber probe 55R55.Findings & Value added: The highest drag coefficient corresponds to the S817 profile. The asymmetry of the airfoil shape has a significant impact on its drag characteristics.Item První pokus PIV měření na kmitajících lopatkách turbínové mříže(Institute of Hydrodynamics CAS, v. v. i., 2022) Tsymbalyuk, Volodymyr; Duda, DanielPro stanovení nestacionárního aerodynamického zatížení (síly a momenty) působícího na lopatky kmitající v proudu plynu na ZČU v Plzni je navrhnout a vystaven aerodynamický stend. Zajímavé je také měření nestacionárního proudového pole za kmitajícím profilem mříže. Udělaná prověrka možnosti nestacionárního měření pomocí PIV zařízeni, které máme v dispozici. Navrhnuta úprava stendu pro další použití PIV metody.Item Přehled některých výsledků laboratoře proudění na Západočeské univerzitě v Plzni od posledního sympózia v roce 2019(Institute of Hydrodynamics CAS, v. v. i., 2022) Duda, Daniel; Yanovych, Vitalii; Uruba, Václav; Horáček, Vít; Martin, Němec; Tomáš, Jelínek; Žitek, Pavel; Abrhám, Vladimír; Petr, Milčák; Kubíková, Tereza; Tomášková, Tetjana; Tsymbalyuk, VolodymyrPřehledový článek o výsledcích a publikacích z let 2019 – 2022. Vše se točí zejména okolo Obrazového měření rychlosti unášených částic (PIV – particle image velocimetry) a žhaveného drátku (CTA – constant temperature anemometry). Tato práce neobsahuje originální výsledky.Item Přehled některých výsledků laboratoře proudění na Západočeské univerzitě v Plzni od posledního sympózia v roce 2019(Institute of Hydrodynamics CAS, v. v. i., 2022) Duda, Daniel; Yanovych, Vitalii; Uruba, Václav; Horáček, Vít; Martin, Němec; Tomáš, Jelínek; Žitek, Pavel; Abrhám, Vladimír; Petr, Milčák; Kubíková, Tereza; Tomášková, Tetjana; Tsymbalyuk, VolodymyrPřehledový článek o výsledcích a publikacích z let 2019 – 2022. Vše se točí zejména okolo Obrazového měření rychlosti unášených částic (PIV – particle image velocimetry) a žhaveného drátku (CTA – constant temperature anemometry). Tato práce neobsahuje originální výsledky.Item On 3D flow pattern behind a wall-mounted circular cylinder of finite-length(American Institute of Physics, 2021) Uruba, Václav; Procházka, PavelItem Wake flow past an ALUTEC profile(EPD Sciences, 2022) Duda, Daniel; Yanovych, Vitalii; Uruba, Václav; Yasar, DokakItem Grid turbulence studied by Particle Image Velocimetry(EPD sciences, 2022) Duda, Daniel; Bém, Jindřich; Yanovych, Vitalii; Uruba, VáclavItem Turbulence topology behind different sections of the wind turbine blade(EPD Sciences, 2022) Yanovych, Vitalii; Duda, Daniel; Uruba, Václav; Kosiak, Pavlo; Horáček, VítItem Vorticity statistics in the near wake of asymmetric prismatic airfoil NACA 64-618 at negative angle of attack –10° at Reynolds numbers 1.6 ⋅ 104 and 1.6 ⋅ 105 in distance 0.0 – 0.4 × chord past trailing edge measured by Particle Image Velocimetry(EPD Sciences, 2022) Narovec, Jan; Duda, Daniel; Horáček, Vít; Tomášková, Tetjana; Uruba, Václav; Yanovych, VitaliiItem Preliminary results of PIV measurement past a stator wheel inside the VT-400 test turbine(EPD Sciences, 2022) Duda, Daniel; Horáček, Vít; Klimko, Marek; Petr, Milčák; Uruba, Václav; Yanovych, Vitalii; Žitek, PavelItem CFD analysis of an anemometric sensor design for air flow measurement in a heat exchanger(EDP Sciences, 2022) Sedláček, Jan; Kůs, Michal; Strob, Miroslav; Matas, RichardTento článek se zaměřuje na problematiku měření průtoku v automobilových výměnících tepla. Měření je komplikované vzhledem k omezenému prostoru v oblasti výměníku tepla a nerovnoměrnému rychlostnímu profilu. Proto lze použít pouze některé měřicí techniky, které je třeba přizpůsobit konkrétním podmínkám. Článek představuje počáteční fáze vývoje žhaveného senzoru pro měření průtoku ve výměníku tepla. Jedná se o CFD simulace, které slouží k určení charakteru proudění v okolí senzoru a ověření jeho vlivu na proudové pole v jeho okolí a na celý výměník tepla. Výsledky těchto počátečních simulací jsou prezentovány a diskutovány.Item Numerical modelling and experimental investigation of the influence of selected geometric elements on the working characteristics of radial compressor stages with prismatic blades(EDP Sciences, 2022) Matas, Richard; Syka, Tomáš; Hurda, Lukáš; Linhartová, ZuzanaČlánek se zabývá popisem vybraných výsledků výzkumu radiálních kompresorových stupňů s 2D, tedy prizmatickými lopatkami. V první části je stručně popsáno experimentální zařízení a postup měření a vyhodnocení. Druhou částí příspěvku je numerická simulace a vyhodnocení vlivu technologických otvorů ve 2D rotorových lopatkách na vlastnosti kompresorového stupně. V poslední části je uveden vliv vůle labyrintových těsnění na pracovní charakteristiky stupně. Je uvedeno a diskutováno srovnání naměřených a vypočtených hodnot.
