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Aeroacoustic Noise Source Investigation in the Case of the Blade Cascade
Procházka, Pavel P.; Antoš, Pavel; Šnábl, Pavel
2022 - anglický
The blade cascade consisted of five NACA 0010 profiles is examined in the framework of project dealing with nonlinear dynamic phenomenon related to stall flutter of flexible profiles with pitch degree of freedom in subsonic flow. Various angles of attack (AoA) of the cascade generates different (broadband) aeroacoustic noise. The goal of this article is to describe the existence of possible noise sources using two experimental methods – Particle Image velocimetry (PIV) and hot-wire (HW) anemometry.
Klíčová slova:
blade cascade; time-resolved PIV; HW anemometry; FFT
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Aeroacoustic Noise Source Investigation in the Case of the Blade Cascade
The blade cascade consisted of five NACA 0010 profiles is examined in the framework of project dealing with nonlinear dynamic phenomenon related to stall flutter of flexible profiles with pitch ...
Temporal, Spatial, and Spatio-temporal correlation of the velocity fluctuations
Jurčáková, Klára
2022 - anglický
Taylor's hypothesis about frozen turbulence [1] says that if the turbulence intensity is small compared to the mean velocity then the advection of a turbulent flow field past a fixed point can be taken entirely due to the mean flow. This means that in the “frozen turbulent field” spatial and temporal dimensions can be interchanged. Although the main assumption of Taylor's hypothesis is not met in the atmospheric boundary layer (the intensity of turbulence is usually between 10 and 20%) the hypothesis is commonly used to calculate integral length scales of turbulent fields from point measurements. Particle image velocimetry with high temporal resolution (TR-PIV) allows us to analyze both temporal and spatial cross-correlations in the turbulent flow fields and to evaluate obtained results.
Klíčová slova:
frozen turbulence; wind tunnel; integral length scales; Particle Image Velocimetry
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Temporal, Spatial, and Spatio-temporal correlation of the velocity fluctuations
Taylor's hypothesis about frozen turbulence [1] says that if the turbulence intensity is small compared to the mean velocity then the advection of a turbulent flow field past a fixed point can be ...
Inverse-Heusler Mn2FeSi alloy prepared by powder metallurgy route
Životský, O.; Skotnicová, K.; Čegan, T.; Juřica, J.; Gembalová, L.; Zažímal, František; Jirásková, Yvonna; Szurman, I.
2022 - anglický
The Mn2FeSi inverse-Heusler alloy was prepared by solid-state reactions using ball milling for 168 h in n hexane. Two milling procedures varying in the ball-to-powder ratio, namely 4:1 and 10:1, were used to follow \ntheir influence on alloy formation and its physical properties. In both cases no Heusler structure was obtained \ndirectly and therefore the subsequent annealing at 1223 K for 1.5 h in pure Ar was applied. The energy dispersive X-ray analysis resulted in the chemical composition about 49.0-49.9 at% Mn, 25.3-25.6 at% Fe, and \n24.8-25.4 at% Si, in a good agreement with nominal one. X-ray diffraction of both powders confirmed inverse Heusler XA structure of lattice parameters 0.5675 nm (4:1) and 0.5677 nm (10:1), only slightly higher as \ntheoretically obtained 0.560 nm. The presence of minor oxidation phases was also observed in the particle \nstructure of powders. Magnetic properties were analysed at low and room temperatures. Both alloys exhibit \nparamagnetic behaviour at room temperature confirmed by transmission Mössbauer spectroscopy \nmeasurements. Different magnetic behaviour of alloys is observed below 65 K.
Klíčová slova:
Heusler alloy, powder, ball milling, microstructure, magnetism; powder; ball milling; microstructure; magnetism
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Inverse-Heusler Mn2FeSi alloy prepared by powder metallurgy route
The Mn2FeSi inverse-Heusler alloy was prepared by solid-state reactions using ball milling for 168 h in n hexane. Two milling procedures varying in the ball-to-powder ratio, namely 4:1 and 10:1, were ...
NANOCERIA PREPARED BY ELECTRON BEAM EVAPORATION
Pizúrová, Naděžda; Hlaváček, A.; Kavčiaková, Zuzana; Roupcová, Pavla; Kuběna, Ivo; Buršík, Jiří; Sokovnin, S. Y.
2022 - anglický
Cerium oxide nanoparticles (nanoceria) are currently one of the most investigated nanomaterials because of their attractive properties used in biomedical applications, catalysis, fuel cells, and many others. These attractive properties are connected with the Ce3+ and Ce4+ valency state ratio. In the nanoparticle form, cerium oxides contain a mixture of Ce3+ and Ce4+ on the nanoparticle surfaces. Switching between these two states requires oxygen vacancies. Therefore, nanoceria's inherent ability to act as an antioxidant in an environmentally-dependent manner and a “redox switch” to confer auto-regenerating capabilities by automatically shifting between Ce4+ and Ce3+ oxidation states is significantly affected by surface morphology. Regarding this demanded behavior, we aimed to characterize synthesized nanoparticle surface quality and its influence on the cerium oxidation states. The received results were used to evaluate the synthesis method's suitability for suggested utilization. We used nanoparticles prepared by electron beam evaporation. This unique physical method includes nanoparticle creation through the fast cooling process followed by breaking radiation damaging nanoparticle surfaces to create surface off-stoichiometry. We prepared a sample containing clusters of a mixture of ultra-small nanoparticles and approximately 100 nm particles. X-ray diffraction confirmed the CeO2 phase in both components. To extract the finest component, we used centrifugal size fractionation. We received 200 nm clusters of 2-10 nm nanoparticles. Nanoparticle shapes and facet types were analyzed using transmission electron microscopy methods. We found out most nanoparticles were formed with truncated octahedrons containing {1,1,1} and {1,0,0} facet types and truncated cuboctahedrons containing {1,1,1}, {1,0,0}, and additional {1,1,0} facets. No octahedron (without truncation) containing only {1,1,1} facets was observed. Nanoparticle shapes containing {1,1,0} and {1,0,0} are suitable for redox activity. Some amount of irregular shapes, beneficial for redox activity, was also observed. Spectroscopy methods confirmed Ce3+ content.
Klíčová slova:
Ce3+ and Ce4+; electron beam evaporation; facet types; hrtem; Nanoceria
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
NANOCERIA PREPARED BY ELECTRON BEAM EVAPORATION
Cerium oxide nanoparticles (nanoceria) are currently one of the most investigated nanomaterials because of their attractive properties used in biomedical applications, catalysis, fuel cells, and many ...
INFLUENCE OF THE DEPOSITION PARAMETERS ON MICROSTRUCTURE AND PROPERTIES OF HVOF SPRAYED WC-CRC-NI COATING
Vražina, Tomáš; Šulák, Ivo; Poloprudský, Jakub; Zábranský, K.; Gejdoš, P.; Hadraba, Hynek; Čelko, L.
2022 - anglický
This paper investigates the influence of thermal spray parameters of the high-velocity oxygen fuel (HVOF) process on the properties of cermet coatings prepared from commercially available Amperit 551 WC-CrC-Ni powder. Three different processing parameters were applied to optimize the production process with the aim to achieve preeminent mechanical properties and fully dense material without microstructural defects. The deposition was carried out by a GLC5 gun. The velocity and temperature of powder particles in the spray stream were monitored by Accuraspray Tecnar diagnostic tool. The quality of deposited coatings was analyzed by means of light microscopy, scanning electron microscopy, and X-ray diffraction. The chemical composition of the used powder and sprayed WC-CrC-Ni coating was determined by energy dispersive spectroscopy. It was found that the spray parameters have a negligible effect on the resulting microstructure and phase composition of the coating. However, the porosity and surface roughness were significantly affected by the variation in process parameters. To assess the basic mechanical properties of HVOF sprayed coating instrumented Vickers hardness measurements were utilized. The coating hardness reached mean values over 1400 HV 0.1 and the indentation modulus varied from 152-279 GPa.
Klíčová slova:
hvof; microhardness; WC-CrC-Ni
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
INFLUENCE OF THE DEPOSITION PARAMETERS ON MICROSTRUCTURE AND PROPERTIES OF HVOF SPRAYED WC-CRC-NI COATING
This paper investigates the influence of thermal spray parameters of the high-velocity oxygen fuel (HVOF) process on the properties of cermet coatings prepared from commercially available Amperit 551 ...
Problematics of aerodynamic damping calculation from measured data of 5-blade cascade
Šnábl, Pavel; Pešek, Luděk; Prasad, Chandra Shekhar; Chindada, Sony
2022 - anglický
Aerodynamic damping as a function of inter-blade phase angle (IBPA), so called S-curve, is crucial for assessment of aeroelastic stability of blade cascades, e.g. turbines, compressors, etc.\nFor constructing the S-curve, the motion-induced controlled flutter is introduced to the bladesof the cascade. As decribed in [1], two testing methods exist: aerodynamic influence coefficient\n(AIC) approach and travelling wave mode (TWM) approach. In TWM approach, all blades in a row oscillate with the same frequency and amplitude with various IBPAs. The response is\nmeasured only on the reference blade. With this approach, several measurements with different IPBAs are needed to construct the S-curve. On the other hand, AIC uses single oscillating\nblade and principle of linear superimposition of aerodynamic influence responses measured on all blades in a cascade. The result of one single measurement can be used for estimation of\naerodynamic damping for any IBPA. In the past year a new 5-blade cascade with rotating symmetrical NACA 0010 profiles was designed and built. The blades of the cascade were placed further apart and thus we are now able to reach stall flutter. Also, the suspension of the blades and sensors were significantly improved. Now, our goal is to evaluate S-curves using AIC approach for different flow conditions and oscillation frequencies.
Klíčová slova:
aerodynamic damping; S-curve; blade cascade
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Problematics of aerodynamic damping calculation from measured data of 5-blade cascade
Aerodynamic damping as a function of inter-blade phase angle (IBPA), so called S-curve, is crucial for assessment of aeroelastic stability of blade cascades, e.g. turbines, compressors, etc.\nFor ...
Long term optical monitoring technique of displacement fields based on ArUco markers
Kunecký, Jiří
2022 - anglický
In structural engineering it is often needed to measure tiny displacements of parts of the structure extremely precisely. For such a purpose it is often needed to use some type of sensor attached to the surface of the structure. This paper presents a new technique which simply uses computer vision libraries to measure displacement of markers originally developed for robotics. Such analysis can be under specific circumstances (2D planar movement) valid if we compare two images taken at different times with the same camera. Main advantage of this method is simplicity of use and low cost of markers, which can be printed in a standard office laser printer. The resolution (error) can be for standard cameras around 0.1 pixel. The method is especially developed for research of timber frames/joints behavior in real structures, because displacements of joints in creep or under load can reach an amplitude which is perfectly detectable by this method.
Klíčová slova:
displacement measurement; long-term monitoring; ArUco markers
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Long term optical monitoring technique of displacement fields based on ArUco markers
In structural engineering it is often needed to measure tiny displacements of parts of the structure extremely precisely. For such a purpose it is often needed to use some type of sensor attached to ...
Analysis of van der Pol equation on slow time scale for combined random and harmonic excitation
Náprstek, Jiří; Fischer, Cyril
2022 - anglický
Vortex shedding represents one of the most important processes that constantly attract the attention of experimental and theoretical research. A number of non-linear effects arise from the fluid-structure interaction. The non-stationary response in the vicinity of the lock-in region has a quasi-periodic character, beating frequency of which varies considerably with the distance from the lock-in frequency. This property is significantly affected by the assumption of combined random and harmonic excitation. This paper describes several details that contribute to the probabilistic characteristics of the system on a time-slow scale using partial response amplitudes.
Klíčová slova:
SDOF oscillator; slow-time system; Fokker-Planck equation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Analysis of van der Pol equation on slow time scale for combined random and harmonic excitation
Vortex shedding represents one of the most important processes that constantly attract the attention of experimental and theoretical research. A number of non-linear effects arise from the ...
Construction of the Lyapunov function reflecting the physical properties of the model
Náprstek, Jiří; Fischer, Cyril
2022 - anglický
Practical experience shows that the random excitation component can affect the system response and its dynamic stability not only negatively but also positively. Such mechanisms are usually developed heuristically and are often not sufficiently justified theoretically. The paper presents a possibility of using the properties of first integrals for the construction of a Lyapunov function for the analysis of a dynamic system stability in the stochastic domain. In such case, the Lyapunov function itself contains information on the examined system and, consequently, it is able to provide a more detailed insight into the system stability properties. The procedure is illustrated by a nonlinear SDOF example.
Klíčová slova:
Lyapunov function; stability; spherical pendulum
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Construction of the Lyapunov function reflecting the physical properties of the model
Practical experience shows that the random excitation component can affect the system response and its dynamic stability not only negatively but also positively. Such mechanisms are usually developed ...
Magnetocrystalline anisotropy of Ni-Mn-Ga-Co-Cu martensite
Rameš, Michal; Straka, Ladislav; Sozinov, A.; Heczko, Oleg
2022 - anglický
The martensites of Heusler alloys based on Ni-Mn-Ga exhibit magnetically-induced reorientation resulting in giant field-induced strain. Up to 12% strain was observed in Ni-Mn-Ga-Co-Cu with 4 at.% of Co and Cu. The driving force of the phenomenon is the magnetocrystalline anisotropy. We studied evolution of the anisotropy with temperature and compositions using magnetiyation curve measurements in four different single crystalline Ni-Mn-Ga-Co-Cu and compared with non-doped Ni-Mn-Ga. The anisotropy of martensite decreases with increasing average doping (Co+Cu)/2 but it does not scale with tetragonal ratio or valence electron concentration.
Klíčová slova:
martensite; magnetocrystalline anisotropy; Heusler alloys; Ni-Mn-Ga
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Magnetocrystalline anisotropy of Ni-Mn-Ga-Co-Cu martensite
The martensites of Heusler alloys based on Ni-Mn-Ga exhibit magnetically-induced reorientation resulting in giant field-induced strain. Up to 12% strain was observed in Ni-Mn-Ga-Co-Cu with 4 at.% of ...
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