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Efficient numerical computation of the steady-state response and stability analysis of the rotor systems with squeeze film dampers
Molčan, M.; Ferfecki, P.; Zapoměl, Jaroslav
2020 - anglický
The aim of this paper is to demonstrate capabilities of the created numerical procedure, which is based on harmonic balance method. Furthermore, the procedure incorporates the alternating frequency-time domain technique and the arc-length parameterization to solve the steady-state response of nonlinear systems in efficient manner, including unstable branches. The stability of the motion was assessed by two methods: the 2n-pass method and Hill’s method. The procedure was verified on an example from literature to prove its sufficient accuracy and subsequently, the procedure was applied on the finite element model of the rotor systém mounted on the squeeze film dampers. The carried out computational simulations confirmed that the created procedure is efficient for the strongly nonlinear response and it gives similar results as the time integration.
Klíčová slova:
harmonic balance method; Floquet theory; Hill’s method; nonlinear forces; flexible rotor
Dokument je dostupný na externích webových stránkách.
Efficient numerical computation of the steady-state response and stability analysis of the rotor systems with squeeze film dampers
The aim of this paper is to demonstrate capabilities of the created numerical procedure, which is based on harmonic balance method. Furthermore, the procedure incorporates the alternating ...
Modification of the Algebraic Transition Model for Wall Roughness Effect Including a Rough Strip
Straka, P.; Příhoda, Jaromír
2020 - anglický
The contribution deals with the simulation of the laminar/turbulent transition on a rough wall. The algebraic transition model taking into account wall roughness according to Straka and Příhoda [8] was further extended for the effect of short rough strip near the leading edge. The proposed correlation was tested by means of incompressible flow over a flat plate covered by sand paper and around the NACA 0012 airfoil with a rough strip near the leading edge. The agreement with experiments is appropriate nevertheless the applicability of the correlation is limited due to the lack of relevant experimental results.
Klíčová slova:
bypass-transition; wall roughness; rough strip
Dokument je dostupný na externích webových stránkách.
Modification of the Algebraic Transition Model for Wall Roughness Effect Including a Rough Strip
The contribution deals with the simulation of the laminar/turbulent transition on a rough wall. The algebraic transition model taking into account wall roughness according to Straka and Příhoda [8] ...
Geometrically realistic macro-scale model for multi-scalesimulations of catalytic filters for automotive gasaftertreatment
Hlavatý, Tomáš; Isoz, Martin; Plachá, M.; Šourek, M.; Kočí, P.
2020 - anglický
This paper is part of a research focused on simulating (i) the catalytic conversion of environment endangering gases, and (ii) trapping of the particulate matter in automotive exhaust gas aftertreatment. Historically, the catalytic conversion and the filtration of soot particles were performed in independent devices. However, recent trend is to combine the catalytic converter and soot filter into a single device, the catalytic filter. Compared to the standard two-device system, the catalytic filter is more compact and has lower heat losses. Nevertheless, it is highly sensitive to the catalyst distribution. This study extends our recently developed methodology for pore-scale simulations of flow, diffusion and reaction in the coated catalytic filters. The extension consists of enabling data transfer from macro- to pore-scale models by preparing geometrically realistic macro-scale CFD simulations. The simulation geometry is based on XRT scans of real-life catalytic filters. The flow data from the newly developed macro-scale model are mapped as boundary conditions into the pore-scale simulations and used to improve the estimates of the catalytic filter filtration efficiency.
Klíčová slova:
CFD; catalytic filter; OpenFOAM
Dokument je dostupný na externích webových stránkách.
Geometrically realistic macro-scale model for multi-scalesimulations of catalytic filters for automotive gasaftertreatment
This paper is part of a research focused on simulating (i) the catalytic conversion of environment endangering gases, and (ii) trapping of the particulate matter in automotive exhaust gas ...
Development of CFD solver for four-way coupled particle-laden flows
Šourek, M.; Isoz, Martin
2020 - anglický
Computational uid dynamics (CFD) simulations containing freely moving bodies are still a challenging topic. More so, if the bodies are large enough to a_ect the uid ow and distributed\ndensely enough to come in contact both with the boundaries of the computational domain and with each other. In this work, we concentrate on the topic of simulation of (i) irregular bodies\nwith ow-induced movement and contact with computational domain boundaries taken into account, and (ii) bodies entrained by the uid and coming in contact not only with the domain\nboundaries but also with each other. The developed modeling approach is based on the hybrid _ctitious domain-immersed boundary method extended by the discrete element method. The\npresent contribution is focused on presentation of simulation principles and results of initial benchmark cases.
Klíčová slova:
CFD; catalytic filter; HFDIB-DEM; OpenFOAM
Dokument je dostupný na externích webových stránkách.
Development of CFD solver for four-way coupled particle-laden flows
Computational uid dynamics (CFD) simulations containing freely moving bodies are still a challenging topic. More so, if the bodies are large enough to a_ect the uid ow and distributed\ndensely enough ...
Study on Performance of Various Turbulent Heat Transfer Closures
Louda, Petr; Příhoda, Jaromír
2020 - anglický
The work compares results of several turbulent heat flux models with different complexity. Authors consider eddy diffusivity model as well as generalized gradient hypothesis and explicit algebraic closures. The results are obtained for backward facing step with heated bottom wall and compared with measurements.
Klíčová slova:
backward facing step; turbulent heat flux
Dokument je dostupný na externích webových stránkách.
Study on Performance of Various Turbulent Heat Transfer Closures
The work compares results of several turbulent heat flux models with different complexity. Authors consider eddy diffusivity model as well as generalized gradient hypothesis and explicit algebraic ...
Large Scale Motions in Turbulent Flows
Kellnerová, Radka; Jurčáková, Klára; Procházka, Pavel P.
2019 - anglický
Quadrant analysis based on the Reynolds decomposition was performed on the data from turbulent boundary layer flows above variously rough surfaces. An estimation of a convective velocity for events significant in terms of momentum flux, and the statistics of a length and amplitude of the individual events, together with their spectral analysis, was performed. Based on the analyses, we were able to detect a few individual sweep and ejection events with a length longer than 6δ, which could be considered as very large scale motions (VLSM). We also identified number of events with a longitudinal dimension equal to approximately 3δ labelled as large scale motions (LSM). The analyses were executed for various Reynolds numbers. The number of detected structures increases with the momentum of the flow.
Klíčová slova:
wind tunnel; large scale motion; quadrant analysis
Dokument je dostupný na externích webových stránkách.
Large Scale Motions in Turbulent Flows
Quadrant analysis based on the Reynolds decomposition was performed on the data from turbulent boundary layer flows above variously rough surfaces. An estimation of a convective velocity for events ...
Assessing Quality of Boundary Layer Flows With the Diagnostic Plot
Jurčáková, Klára; Procházka, Pavel P.; Kellnerová, Radka
2019 - anglický
We experimentally investigated turbulent boundary layers over 4 rough surfaces and 1 smooth surface by particle image velocimetry for a range a free stream velocities. The obtained mean velocity vertical profiles were universally scaled by roughness length z₀ and friction velocity u*, but both parameters have to be obtained from the fit of the logarithmic or composite velocity pro le to the experimental data. Diagnostic plot, which relates turbulence intensity with the mean velocity showed good collapse of different free stream velocities for each surface. It became fully universal in its modified version when the roughness function was taken into an account. We found that turbulence intensities over our surfaces are higher than any published one and that they dependent on roughness length z₀*.
Klíčová slova:
wind tunnel; turbulence intensity; rough-wall; friction velocity
Dokument je dostupný na externích webových stránkách.
Assessing Quality of Boundary Layer Flows With the Diagnostic Plot
We experimentally investigated turbulent boundary layers over 4 rough surfaces and 1 smooth surface by particle image velocimetry for a range a free stream velocities. The obtained mean velocity ...
Structure of the Wake Behind an Airfoil
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2019 - anglický
The wake behind an inclined plate simulating airfoil is to be studied experimentally. The vortical structures are identified eventually. Theirs topology and dynamical behaviour is to be studied in details using the Proper Orthogonal Decomposition method. The stereo time resolved Particle Image Velocimetry technique is used for the experimental research. The vortex trains with oblique orientation and chequered topology have been detected.
Klíčová slova:
airfoil; boundary layer; wake; instability
Dokument je dostupný na externích webových stránkách.
Structure of the Wake Behind an Airfoil
The wake behind an inclined plate simulating airfoil is to be studied experimentally. The vortical structures are identified eventually. Theirs topology and dynamical behaviour is to be studied in ...
Finite element modelling of elastic wave propagation in heterogeneous media
Kolman, Radek; Cho, S.S.; González, J. A.; Park, K.C.
2019 - anglický
In this contribution, we present an explicit scheme based on local time stepping respecting local wave speed and local stability limit for each finite element. The work aim is to suppress the spurious oscillations in wave propagation tasks in heterogeneous bars.
Klíčová slova:
finite element modelling; elastic wave; heterogeneous media
Dokument je dostupný na externích webových stránkách.
Finite element modelling of elastic wave propagation in heterogeneous media
In this contribution, we present an explicit scheme based on local time stepping respecting local wave speed and local stability limit for each finite element. The work aim is to suppress the spurious ...
The measurement of the heterogeneous particles in the steam
Bartoš, Ondřej; Hrubý, Jan; Ždímal, Vladimír; Kolovratník, Michal; Jiříček, I.; Moravec, Pavel; Zíková, Naděžda
2019 - anglický
The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of droplets in low-pressure steam turbines has a significant impact on the efficiency of energy conversion due to the strongly nonequilibrium nature of this process . The condensed water also erodes the turbine blades. A very important question is to what extent heterogeneous nucleation contributes to the phase transition process . In the case of heterogeneous nucleation , the number of droplets depends only on the number of h eterogeneous particles in the system, whereas in the case of homogeneous nucleation, the number of created droplets is determined rather by the expansion rate - in a faster expansion, greater supersaturation and more droplets are formed until the released condensation enthalpy quenches the nucleation.\nThe specific number of droplets (number of droplets per unit mass of steam) formed in the turbine can be determined by optical probes, developed first by Walters and later in the Czech Republic improved by Petr and Kolovratník. Until recently, no information was available on the relative importance of heterogeneous nucleation in forming these droplets.
Klíčová slova:
heterogeneous nucleation; steam turbine; ultrafine aerosol particles
Dokument je dostupný na externích webových stránkách.
The measurement of the heterogeneous particles in the steam
The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of ...
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