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Item Flutter Measurement of a Linear Turbine Blade Cascade with an Angular Position Deviation of One Blade(2023) Eret, Petr; Tsymbalyuk, Volodymyr; Eckert, MarkusExperimental flutter testing of high-aspect ratio rotor blades is a mainstay of turbomachinery research. However, rotor blades are never identical, and geometrical errors between actual and nominal geometries exist due to limited machining precision or assembly imperfection. The paper presents the initial phase of the controlled flutter research of a linear turbine blade cascade with a geometric deviation in one blade position. A subsonic wind tunnel with four flexibly mounted blades in an otherwise rigid blade cascade is employed at one angle of incidence and three low reduced frequencies. Measurements are performed with an angular position deviation (±1.5°) of one blade in pure bending and torsion modes. A tangible effect of one blade’s slight incidence angle offset on the vibrating blade cascade aerodynamic stability is demonstrated, and this research effort opens the door to a more extensive testing campaign.
Item Influence of fluidelastic vibration frequency on predicting damping controlled instability using a quasi-steady model in a normal triangular tube array(2024) Eret, PetrResearchers have applied theoretical and CFD models for years to analyze the fluidelastic instability (FEI) of tube arrays in steam generators and other heat exchangers. The accuracy of each approach has typically been evaluated using the discrepancy between the experimental critical flow velocity and the predicted value. In the best cases, the predicted critical flow velocity was within an order of magnitude comparable to the measured one. This paper revisits the quasi-steady approach for damping controlled FEI in a normal triangular array with a pitch ratio of P/d=1.375. The method addresses the fluidelastic frequency at the stability threshold as an input parameter for the approach. The excellent agreement between the estimated stability thresholds and the equivalent experimental results suggests that the fluidelastic frequency must be included in the quasi-steady analysis, which requires minimal computing time and experimental data. In addition, the model allows a simple time delay analysis regarding flow convective and viscous effects.Item Wakes and secondary structures past stator wheel in test turbine VT-400 observed by PIV(2024) Duda, Daniel; Klimko, Marek; Milčák, Petr; Jeřábek, Matěj; Uruba, Václav; Yanovych, Vitalii; Žitek, PavelFlow inside the axial test turbine VT-400 is measured by using a standard methodology of Particle Image Velocimetry (PIV). The studied area lies between the stator and rotor wheel in meridional plane. This area covers both: the regular flow near hub and the endwall secondary structures as well. Regular structure of wakes and jets past stator blades is observed in terms of mean velocities and turbulence intensity. The fluctuations are close to isotropy and the energy distribution across length-scales exhibits almost Kolmogorov scaling. Near the hub, we observe secondary vortices. Despite the positive radial ejections in that regions, these secondary vortices drift towards the hub, they dissipate energy and circulation and their core grows in size.Item Interaction of stream-wise vortices generated by swirler grid(2024) Duda, Daniel; Yanovych, VitaliiA system of stream-wise vortices has been created using a grid of swirling elements with alternating orientations (like a chessboard). The particle image velocimetry method has been used to map the velocity field in several planes perpendicular to the stream. The mesh-based Reynolds number is 1.35 × 10 4 and 2.71 × 10 4 , respectively. The stream-wise development of turbulent kinetic energy (TKE) shows first an increase in a distance of x ≈ 10 M , followed by power-law decay. Individual vortices are detected in each snapshot. The radial profile of TKE transformed to a vortex coordinate system is almost constant, either with maximum as in static frame or zero as observed by previous research. The properties of detected vortices are studied statistically: the meandering amplitude expressed as the standard deviation of vortex positions grows roughly as ∼ e x , i.e., faster than expected random-walk growth ∼ x . Vortex circulation decays exponentially as predicted by classical Helmholtz theorem. The interaction between neighboring vortices is expressed via correlation of selected quantities. Correlation of energy develops downstream from anticorrelation to a positive correlation. The strongest correlation is observed between the first vortex circulation and the second vortex position perpendicular to their connection line. Other correlations are weak.Item Analysis of geometric errors of throat sizes of last stage blades in a mid-size steam turbine(2022) Eret, Petr; Hoznedl, MichalSteam turbine technology with enhanced flexibility will continue to participate in electric power supply mixes. Last stage blades secure the reliability of a steam turbine and require high precision manufacturing and assembly. This case study presents a statistical analysis of geometric errors of the throat sizes of the last stage blades in a mid-size steam turbine. A 3D optical scanner is employed to capture detailed geometries of rotor blades and a half of assembled nozzle diaphragm. Unrolled cylinder cross-sections are used to evaluate 2D geometrical features such as blade throats and areas at three different diameters, and the results are compared to intended designs. In addition, linear correlations between the throat size and blade pitch, area and trailing edge thickness are established, and blade throat position shifts are quantified. Such a comprehensive study is presented for the first time, and some useful conclusions can be retrieved from this case study.Item PANDA Phase One(2021) Duda, Daniel; PANDA, CollaborationThe Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, provides unique possibilities for a new generation of hadron-, nuclear- and atomic physics experiments. The future antiProton ANnihilations at DArmstadt (PANDA or PANDA) experiment at FAIR will offer a broad physics programme, covering different aspects of the strong interaction. Understanding the latter in the non-perturbative regime remains one of the greatest challenges in contemporary physics. The antiproton-nucleon interaction studied with PANDA provides crucial tests in this area. Furthermore, the high-intensity, low-energy domain of PANDA allows for searches for physics beyond the Standard Model, e.g. through high precision symmetry tests. This paper takes into account a staged approach for the detector setup and for the delivered luminosity from the accelerator. The available detector setup at the time of the delivery of the first antiproton beams in the HESR storage ring is referred to as the Phase One setup. The physics programme that is achievable during Phase One is outlined in this paper.Item The potential of Λ and Ξ- studies with PANDA at FAIR(2021) Duda, Daniel; PANDA, CollaborationThe antiproton experiment PANDA at FAIR is designed to bring hadron physics to a new level in terms of scope, precision and accuracy. In this work, its unique capability for studies of hyperons is outlined. We discuss groundstate hyperons as diagnostic tools to study non-perturbative aspects of the strong interaction, and fundamental symmetries. New simulation studies have been carried out for two benchmark hyperon-antihyperon production channels: (p) over barp -> (Lambda) over bar Lambda and (p) over barp -> (Xi) over bar+Xi(-). The results, presented in detail in this paper, show that hyperon-antihyperon pairs from these reactions can be exclusively reconstructed with high efficiency and very low background contamination. In addition, the polarisation and spin correlations have been studied, exploiting the weak, self-analysing decay of hyperons and antihyperons. Two independent approaches to the finite efficiency have been applied and evaluated: one standard multidimensional efficiency correction approach, and one efficiency independent approach. The applicability of the latter was thoroughly evaluated for all channels, beam momenta and observables. The standard method yields good results in all cases, and shows that spin observables can be studied with high precision and accuracy already in the first phase of data taking with PANDA.Item Effect of Manufacturing Processes on Blade Throat Size and Position in a Steam Turbine Diaphragm(2022) Eret, Petr; Hoznedl, MichalDespite a sustainable energy future, steam turbines are requisite for the reliability and security of the electric power supply in many countries. Accurate and precise manufacturing of the steam path is crucial to turbine efficiency. Before entering the rotor blades, the steam must be correctly guided using stationary blading in a diaphragm. Steam turbine diaphragms are complicated components to manufacture, and welding is the most common fabrication method. A case study presented in this paper employs data from a 3D optical scanner for a geometric deviation analysis of the upper half of the diaphragm at two production steps, after complete welding and after final machining. Unrolled cylinder cross-sections at different diameters are used to evaluate the blade throat sizes and positions compared to the nominal geometry. The results indicate significant geometric changes between the two fabrication steps, and several suggestions are put forward for targeted future work.Item Study of excited Ξ baryons with the (P)over-barANDA detector(2021) Duda, Daniel; PANDA, CollaborationThe study of baryon excitation spectra provides insight into the inner structure of baryons. So far, most of the world-wide efforts have been directed towards N * and Delta spectroscopy. Nevertheless, the study of the double and triple strange baryon spectrum provides independent information to the N * and Delta spectra. The future antiproton experiment (P) over bar ANDA will provide direct access to final states containing a (Xi) over bar Xi pair, for which production cross sections up to mu b are expected in (p) over barp reactions. With a luminosity of L = 10(31) cm(-2) s(-1) in the first phase of the experiment, the expected cross sections correspond to a production rate of similar to 10(6) events/day. With a nearly 4 pi detector acceptance, (P) over bar ANDA will thus be a hyperon factory. In this study, reactions of the type (p) over barp -> (Xi) over bar (+)Xi*(-) as well as (p) over barp -> (Xi) over bar*(+)Xi(-) with various decay modes are investigated. For the exclusive reconstruction of the signal events a full decay tree fit is used, resulting in reconstruction efficiencies between 3 and 5%. This allows high statistics data to be collected within a few weeks of data taking.Item Feasibility studies for the measurement of time-like proton electromagnetic form factors from (p)over-barp → μ+μ- at PANDA at FAIR(2021) Duda, Daniel; PANDA, CollaborationThis paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, | GE| and | GM| , using the p¯ p→ μ+μ- reaction at P ¯ ANDA (FAIR). The electromagnetic form factors are fundamental quantities parameterizing the electric and magnetic structure of hadrons. This work estimates the statistical and total accuracy with which the form factors can be measured at P ¯ ANDA , using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is p¯ p→ π+π-, due to the very similar behavior of muons and pions in the detector. The suppression factors are evaluated for this and all other relevant background channels at different values of antiproton beam momentum. The signal/background separation is based on a multivariate analysis, using the Boosted Decision Trees method. An expected background subtraction is included in this study, based on realistic angular distributions of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented.Item Erosion Effect on Wind Turbine Blades Performance(2024) Yanovych, Vitalii; Duda, Daniel; Uruba, Václav; Klimko, Marek; Žitek, PavelThis paper investigates the effects of surface erosion on the aerodynamic efficiency of wind turbine blades. The experimental study utilized an asymmetric airfoil profile with various surface textures and trailing edge configurations. Tests were conducted across a range of flow velocities and angles of incidence. Flow topology was analyzed using Constant Temperature Anemometry and Particle Image Velocimetry, while aerodynamic properties were assessed using an aerodynamic balance in multiple experimental scenarios. The results reveal a significant impact of even minor surface degradation on blade aerodynamics. Specifically, at a chord-based Reynolds number of 1.7 × 10^5 and a zero angle of incidence, the lift coefficient for blades with an ideal surface condition is up to seven times higher than for configurations featuring rough surfaces and blunt trailing edges.
Item Experimental Subsonic Flutter of a Linear Turbine Blade Cascade With Various Mode Shapes and Chordwise Torsion Axis Locations(ASME, 2023) Eret, Petr; Tsymbalyuk, VolodymyrItem Numerical Simulation of Ammonia-Water Solution Based Heat Absorber(Technical University of Košice, 2022) Volf, Michal; Jeřábek, Matěj; Demianenko, MarynaItem Influence of surface roughness on the wake structure of a circular cylinder at Reynolds number 5× 103 to 12× 103(Elsevier, 2022) Michálek, Petr; Procházka, Pavel; Uruba, Václav; Stanislav, PospíšilItem Investigation of Low-Frequency Phenomena within Flow Pattern in Standard Mixing Vessel Induced by Pitched Blade Impeller(MDPI, 2021) Brůha, Tomáš; Procházka, Pavel; Uruba, VáclavItem Experimental and Numerical Study on Vortical Structures and Their Dynamics in a Pump Sump(MDPI, 2022) Uruba, Václav; Procházka, Pavel; Sedlář, Milan; Komárek, Martin; Duda, DanielItem Dynamics of flow in a branching channel(EDP Sciences, 2021) Uruba, Václav; Procházka, Pavel; Skála, VladislavItem Low-pressure turbine blade leading edge protection using robotic laser cladding technology(Springer, 2022) Vaníček, Ondřej; Chaluš, Michal; Liška, Jindřich; Glusa, Tomáš; Vlasák, Jakub; Vašíčková, Eva; Brom, KarelItem Surface Tension in the Supercooled Water Region(Springer, 2021) Kalová, Jana; Mareš, RadimVoda vykazuje četné anomálie. Pro vysvětlení těchto anomálií byly navrženy různé scénáře. Podle těchto scénářů se očekává postupné zvyšování povrchového napětí s klesající teplotou. Zjevný experimentální důkaz anomálie druhého inflexního bodu (SIP) však stále chyběl. Nedávno Hrubý et al. (J Phys Chem Lett, 11: 443, 2020) publikovali nový experiment, který poskytuje prostor pro další diskusi o existenci SIP v oblasti přechlazené vody. Naše skupina použila metodu kapilárního vzlínání a měřila povrchové napětí vody až do teploty -32,27 °C. V článku ukážeme, že výsledky obou experimentů nepotvrzují existenci SIP v hluboce podchlazené vodě. Měření pro velmi nízké teploty však ukazují, že extrapolovanou formulaci IAPWS R1-76 (2014) nelze doporučit pro teploty pod - 25 °C.Item Temperature Dependence of the Surface Tension of Water, Including the Supercooled Region(Springer, 2022) Kalová, Jana; Mareš, RadimPro závislost povrchového napětí vody na teplotě se nejčastěji používá rovnice formulovaná již v roce 1976 Mezinárodní asociací pro vlastnosti vody a páry (IAPWS). Existují důvody pro zásadní revizi této rovnice. V tomto článku kriticky analyzujeme stávající experimentální údaje a hodnotíme pokusy o vytvoření alternativní rovnice ke standardu IAPWS. Testovali jsme různé formy korelace pro závislost povrchového napětí vody na teplotě. Rozhodli jsme se použít Wegnerovu formu popisu termofyzikálních vlastností v blízkosti kritického bodu s pevnými teoretickými exponenty. Tato korelace dobře popisuje experimentální data v rozsahu od 240,88 K do 647,096 K. Odhadovaná nejistota se pohybuje s teplotou od 0,1 mN-m-1 (pro teploty pod 288,15 K) do 0,2 mN-m-1 pro teploty kolem 373,15 K.
