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    Wyświetlanie 1-6 z 6
    Tytuł:
    What is the role of the stagnation region in Karman vortex shedding?
    Autorzy:
    Pankanin, G. L.
    Powiązania:
    https://bibliotekanauki.pl/articles/221765.pdf
    Data publikacji:
    2011
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    flow measurement
    Karman vortex shedding
    bluff body
    stagnation region
    Opis:
    This paper is devoted to the problem of the appearance of a stagnation region during Karman vortex shedding. This particular phenomenon has been addressed by G. Birkhoff in his model of vortices generation. Experimental results obtained by various research methods confirm the existence of a stagnation region. The properties of this stagnation region have been described based on experimental findings involving flow visualisation and hot-wire anemometry. Special attention has been paid to the relationship between the existence of a slit in the bluff body and the size of the stagnation region. The slit takes over the role of the stagnation region as an information channel for generating vortices.
    Źródło:
    Metrology and Measurement Systems; 2011, 18, 3; 361-370
    0860-8229
    Pojawia się w:
    Metrology and Measurement Systems
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Experimental study on suppression of vortex street behind perforated square cylinder
    Autorzy:
    Teimourian, A.
    Hacışevki, H.
    Bahrami, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/279942.pdf
    Data publikacji:
    2017
    Wydawca:
    Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
    Tematy:
    vortex shedding
    flow control
    coherent flow structure
    perforated square cylinder
    Opis:
    In this study, the effects of entrainment of a fluid through a perforated surface on suppression of the vortex street behind a perforated square cylinder have been studied experimentally. The wake region has been investigated in terms of coherent flow structure, time averaged properties and effectiveness of different perforations. The quantitative measurements revealed that the perforated surfaces are only effective within a width interval of y/D = ±1.0. It has been observed that in the near wake region up to approximately 1.5D downstream the wake, the shedding phenomenon has been suppressed significantly. It has been also demonstrated that velocity profiles and flow structure have been affected by different perforated surfaces and, as a result, coherent structures have been diminished considerably.
    Źródło:
    Journal of Theoretical and Applied Mechanics; 2017, 55, 4; 1397-1408
    1429-2955
    Pojawia się w:
    Journal of Theoretical and Applied Mechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Numerical analysis of controlling separation in axial cascades by excitation of periodical incoming wake
    Autorzy:
    Liu, F.
    Wang, J.
    Wu, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933188.pdf
    Data publikacji:
    2008
    Wydawca:
    Politechnika Gdańska
    Tematy:
    unsteady excitation
    compressor cascade
    separation control
    incoming wake
    vortex shedding
    Opis:
    Numerical analysis has been performed of time-space structures in a large turning angle axial cascade subject to unsteady incoming wake excitation. The results have shown that intentional unsteady excitation could increase the cascade's time-averaged performance. As a result, the vortex structures corresponding to the external exciting frequency are strengthened and other disordered vortices are involved, so that the separation structures of the suction surface are translated from disorder to order. Two interaction regimes between incoming periodic wakes and separation structures are analyzed, indicating that turbulent kinetic energy can enhance momentum interchange and that wave-vortex resonance can promote rolled-up and plus-minus pairing of vortices. Based .on these, responses of separation structures from two periodic incoming wake regimes are compared. The feasibility of far-field noise reduction in ducting fans by using periodic incoming wake is considered.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2008, 12, 1-2; 21-34
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Badania modelowe liczby Strouhala oblodzonego cięgna mostu podwieszonego
    Model investigations of Strouhal number of iced cable of cable-stayed bridge
    Autorzy:
    Górski, P.
    Pospišil, S
    Kuznetsov, S
    Tatara, M.
    Marušić, A
    Powiązania:
    https://bibliotekanauki.pl/articles/391183.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Lubelska. Wydawnictwo Politechniki Lubelskiej
    Tematy:
    aerodynamika
    oblodzenie
    cięgno
    liczba Strouhala
    wzbudzenie wirowe
    aerodynamic
    icing
    cable
    Strouhal number
    vortex shedding
    Opis:
    W artykule przedstawiono sposób i wyniki badań liczby Strouhala nieruchomego modelu oblodzonego cięgna mostu podwieszonego. Badania wykonano w tunelu aerodynamicznym z komorą klimatyczną Laboratorium Czeskiej Akademii Nauk w Telc. W komorze klimatycznej wykonano doświadczalne oblodzenie modelu cięgna o osi nachylonej pod kątem 300 do płaszczyzny poziomej. Kształt oblodzonej powierzchni zarejestrowano metodą fotogrametrii cyfrowej. Do badań w tunelu aerodynamicznym wykonano nowy model sekcyjny oblodzonego cięgna metodą druku 3D. Liczbę Strouhala wyznaczono w zakresie wartości liczby Reynoldsa od 28 do 122 na podstawie pomiaru częstości odrywania się wirów w śladzie aerodynamicznym za modelem.
    The paper presents the method and results of wind tunnel investigations of Strouhal number of stationary iced cable model of cable-stayed bridge. The investigations were performed in a Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in Telc. The experimental icing of the inclined cable model in the climatic chamber of the laboratory was made. The shape of the iced model was registered by a numerical photogrammetry method. For the aerodynamic tunnel investigations, the new iced cable model was made by using 3D printing method. The Strouhal number was determined within the range of the Reynolds number between 28·103 and 122·103, on the basis of the dominant vortex shedding frequency measured in the flow behind the model.
    Źródło:
    Budownictwo i Architektura; 2014, 13, 2; 201-208
    1899-0665
    Pojawia się w:
    Budownictwo i Architektura
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Numerical investigation of vortex wake patterns of laminar flow around two side-by-side cylinders
    Autorzy:
    Nguyen, Van Luc
    Ho, Duy Khanh
    Powiązania:
    https://bibliotekanauki.pl/articles/27309846.pdf
    Data publikacji:
    2022
    Wydawca:
    Polska Akademia Nauk. Czasopisma i Monografie PAN
    Tematy:
    viscous fluid
    vortex shedding
    vortex wake pattern
    vortex-in-cell method
    two side-by-side cylinders
    lepki płyn
    wir
    wzór budzenia wirowego
    metoda wirowania w komórce
    Opis:
    The laminar flow around two side-by-side circular cylinders was numerically investigated using a vortex-in-cell method combined with a continuous-forcing immersed boundary method. The Reynolds number (Re) of the flow was examined in the range from 40 to 200, and the distance between the cylinders varies from 1.2D to 6D, where D is the cylinder diameter. Simulation results show that the vortex wake is classified into eight patterns, such as single-bluff-body, meandering-motion, steady, deflected-in-one-direction, flip-flopping, anti-phase-synchronization, in-phase-synchronization, and phase-difference-synchronization, significantly depending on the Re, the cylinder distance, and the initial external disturbance effects. The anti-phase-synchronization, in-phase-synchronization, and phase-difference-synchronization vortex patterns can be switched at a low Re after a long time evolution of the flow. In particular, the single-bluff-body and flip-flopping vortex patterns excite the oscillation amplitude of the drag and lift coefficients exerted on the cylinders
    Źródło:
    Archive of Mechanical Engineering; 2022, LXIX, 3; 541--565
    0004-0738
    Pojawia się w:
    Archive of Mechanical Engineering
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Numerical Prediction of the Tonal Airborne Noise for a NACA 0012 Aerofoil at Moderate Reynolds Number Using a Transitional URANS Approach
    Autorzy:
    De Gennaro, M.
    Küehnelt, H.
    Zanon, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/178116.pdf
    Data publikacji:
    2017
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    tonal airborne noise
    NACA 0012
    Laminar Boundary Layer-Vortex Shedding noise
    Ladder-like tonal structure of the acoustic spectrum
    multi-tonal structure of the acoustic spectrum
    Opis:
    Tonal airborne noise of aerofoils appears in a limited range of moderate Reynolds numbers and angles of attack. In these specific conditions, the aerofoil is characterised by a large region of laminar flow over the aerodynamic surface, typically resulting in two-dimensional laminar instabilities in the boundary layer, generating one or more acoustic tones. The numerical simulation of such phenomenon requires, beside an accurate prediction of the unsteady flow field, a proper modelling of the laminar to turbulent transition of the boundary layer, which generally imposes the use of highly CPU demanding approaches such as large eddy simulation (LES) or direct numerical simulation (DNS). This paper aims at presenting the results of numerical experiments for evaluating the capability of capturing the tonal airborne noise by using an advanced, yet low computationally demanding, unsteady Reynolds-averaged Navier-Stokes (URANS) turbulence model augmented with a transitional model to account for the laminar to turbulent transition. This approach, coupled with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy, is adopted for predicting the far-field acoustic sound pressure of a NACA 0012 aerofoil with Reynolds number ranging from 0.39 · 106 to 1.09 · 106. The results show a main tone located approximately at 1.6–1.8 kHz for a Reynolds number equal to 0.62 · 106, increasing to 2.4 kHz at Reynolds number equal to 0.85 · 106 and 3.4 kHz at 1.09 · 106, while no main tones are observed at 0.39 · 106. The computed spectra confirm that the acoustic emission of the aerofoil is dominated by tonal structures and that the frequency of the main tone depends on the Reynolds number consistently with the ladder-like tonal structure suggested by Paterson et al. Moreover, in specific conditions, the acoustic spectra exhibit a multi-tonal structure visible in narrowband spectra, in line with the findings of Arbey and Bataille. The presented results demonstrate the capability of the numerical model of predicting the physics of the tonal airborne noise generation.
    Źródło:
    Archives of Acoustics; 2017, 42, 4; 653-675
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
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