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    Wyświetlanie 1-8 z 8
    Tytuł:
    On the turbulent boundary layer of a dry granular avalanche down an incline. II – closure model and numerical simulations
    Autorzy:
    Fang, C.
    Powiązania:
    https://bibliotekanauki.pl/articles/279373.pdf
    Data publikacji:
    2016
    Wydawca:
    Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
    Tematy:
    closure model
    gravity-driven flow
    passive layer
    turbulent boundary layer
    Opis:
    Dynamic responses of the closure relations, specific turbulent Helmholtz free energy and turbulent viscosity are postulated followed by experimental calibrations. The established closure model is applied to analyses of a gravity-driven stationary avalanche with incompressible grains down an incline. While the mean velocity and volume fraction increase from their minimum values on the plane toward maximum values on the free surface exponentially, two-fold turbulent kinetic energies and dissipations evolve in a reverse manner. Most two-fold turbulent kinetic energies and dissipations are confined within the thin turbulent boundary layer immediately above the plane, with nearly vanishing two-fold turbulent kinetic energies and finite two-fold turbulent dissipations in the passive layer. The two layers are similar to those of Newtonian fluids in turbulent boundary layer flows, and are preferable recognized by the distributions of turbulent kinetic energies and dissipations.
    Źródło:
    Journal of Theoretical and Applied Mechanics; 2016, 54, 4; 1245-1256
    1429-2955
    Pojawia się w:
    Journal of Theoretical and Applied Mechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Skin friction estimation in a strong decelerating flow
    Autorzy:
    Dróżdż, A.
    Elsner, W.
    Sikorski, D.
    Powiązania:
    https://bibliotekanauki.pl/articles/279383.pdf
    Data publikacji:
    2018
    Wydawca:
    Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
    Tematy:
    turbulent boundary layer
    separation
    oil-film interferometry
    Clauser chart
    Opis:
    The paper presents the analysis of the turbulent boundary layer developed on a flat plate subjected to an Adverse Pressure Gradient (APG) and approaching separation. The aim of the study is to examine the effects of pressure gradient on a non-equilibrium boundary layer while indicating local areas of the equilibrium flow. The emphasis is on the analysis of mean flow velocity and the estimation of skin friction. It is known that accurate measurements of skin friction were considered as a difficult and demanding task despite of various measuring techniques available. A great challenge is especially the measurement of a strong decelerated turbulent boundary layer because of low shear stress and possible large measuring errors. To date, the oil film or oil drop interferometry technique, because of its high accuracy, has become a basis of turbulent-boundary-layer research. In our research, this technique has been used as a reference method for comparing with the traditional Clauser chart method, which generally is considered as not suitably for non-canonical flows. In the paper, however, a correction of the method is proposed, which allows one to increase its range of applicability. This corrected Clauser chart method (CCCM) involves only one iteration while other proposed in the literature methods employ a twofold iterative procedure. The comparison of the methods for the non-canonical turbulent boundary layer, i.e. adverse pressure gradient with a strong flow history effect has been presented. It has been shown that CCCM can be successfully used for small and medium pressure gradients, where the Clauser-Rotta pressure gradient parameter β does not exceed level close to 11.
    Źródło:
    Journal of Theoretical and Applied Mechanics; 2018, 56, 2; 365-376
    1429-2955
    Pojawia się w:
    Journal of Theoretical and Applied Mechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Comparison of single and X-wire measurements of streamwise velocity fluctuations in turbulent boundary layer
    Autorzy:
    Dróżdż, A.
    Elsner, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/281655.pdf
    Data publikacji:
    2014
    Wydawca:
    Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
    Tematy:
    turbulent boundary layer
    energy spectra
    hot-wire spatial resolution
    Opis:
    The paper discusses the problem of measuring velocity fluctuations of a turbulent boundary layer using single and X-wire probes. It seems that the difference between the streamwise fluctuating component of these two probes results not only from spatial resolution, but also from influence of the wall-normal fluctuating component, which is usually not considered. It was shown that the vector summing these two components obtained from X-wire probe gives the shape of fluctuation distribution obtained from a single-wire probe. It implies that the underestimation of the near-wall peak of streamwise fluctuating component in X-wire measurements results from disregarded wall-normal fluctuations, which is obviously taken in the case of a single-wire probe. Moreover, it was shown that the criteria for wire length i.e. l+ ≤ 20 could not be sufficient to properly estimate the streamwise and wall-normal fluctuations.
    Źródło:
    Journal of Theoretical and Applied Mechanics; 2014, 52, 2; 499-505
    1429-2955
    Pojawia się w:
    Journal of Theoretical and Applied Mechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    LES of converging-diverging channel flow with separation
    Autorzy:
    Kuban, L.
    Elsner, W.
    Tyliszczak, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1943209.pdf
    Data publikacji:
    2010
    Wydawca:
    Politechnika Gdańska
    Tematy:
    LES
    turbulent boundary layer
    separation
    channel flow
    pressure gradient
    Opis:
    The paper presents the results of LES simulation of two different turbulent channels with inlet conditions corresponding to the Reynolds number Re =395. In both cases a varying pressure gradient was obtained by an adequate curvature of one of the walls. The first case is treated as a benchmark and is used to validate the numerical procedure. This case is characterized by the same cross-section area at the inlet and outlet and a bump of a smooth profile located on one of the walls designed to be identical to the one used in the experiment conducted at Laboratorie de Mecanique de Lille (LML) (Marquillie et al., 2008). The second case corresponds to the geometry which reproduces the real geometry of the turbomachinery test section of the Czestochowa University of Technology. The test section was created in such a way as to produce the pressure gradient which would correspond to the conditions present in the axial compressor blade channel. The shape of both channels produced initially favorable (FPG) and then adverse pressure gradients (APG), and in this way created conditions for boundary layer separation. Due to a reverse flow where the turbulence transport is dictated by the dynamics of the large-scale eddies such a case is well suited to demonstrate predictive features of the LES technique.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2010, 14, 3; 283-295
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Application of the diagnostic plot in estimation of the skin friction in turbulent boundary layer under an adverse pressure gradient
    Autorzy:
    Niegodajew, P.
    Dróżdż, A.
    Elsner, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/38622693.pdf
    Data publikacji:
    2021
    Wydawca:
    Instytut Podstawowych Problemów Techniki PAN
    Tematy:
    turbulent boundary layer
    friction velocity
    Clauser-chart
    adverse pressure gradient
    diagnostic plot
    Opis:
    The paper concerns the problem of determining friction velocity in wallbounded flows affected by an adverse pressure gradient (APG). In the work of Niegodajew et al. [22] the corrected Clauser chart method (CCCM) for such flow conditions was proposed. This approach utilises the mean velocity profiles and turbulence intensity profiles to accurately estimate the friction velocity. In another work, Drózdz et al. [27] presented a modified version of the diagnostic-plot scaling (DPS) which allows for direct reconstruction of turbulence intensity profiles based on the local mean velocity profile, even when the flow is affected by a strong pressure gradient. This paper is aimed at verifying whether, when combining both of these methods (i.e. DPS and CCCM), the friction velocity can be accurately determined for APG flow conditions and one can possibly take advantage from both methods. The analysis revealed that the new approach is able to predict the friction velocity with uncertainty less than 5% for all the considered cases for the Clauser–Rotta parameter β < 17. Lastly, DPS-CCCM was also confronted with two empirical approaches (from available literature) allowing for estimation of the friction velocity under APG conditions. The performance of DPS-CCCM was found to be better than the ones of two other empirical approaches.
    Źródło:
    Archives of Mechanics; 2021, 73, 2; 201-215
    0373-2029
    Pojawia się w:
    Archives of Mechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Effect of Angle of Attack and Flow Conditions on Turbulent Boundary Layer Noise of Small Wind Turbines
    Autorzy:
    Afanasieva, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/177922.pdf
    Data publikacji:
    2017
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    wind turbine
    airfoil self-noise
    turbulent boundary layer
    flow conditions
    angle of attack
    Opis:
    The article aims to solve the problem of noise optimization of small wind turbines. The detailed analysis concentrates on accurate specification and prediction of the turbulent boundary layer noise spectrum of the blade airfoil. The angles of attack prediction for a horizontal axis wind turbine (HAWT) and the estimation based on literature data for a vertical axis one (VAWT), were conducted, and the influence on the noise spectrum was considered. The 1/3-octave sound pressure levels are obtained by semi-empirical model BPM. Resulting contour plots show a fundamental difference in the spectrum of HAWT and VAWT reflecting the two aerodynamic modes of flow that predefine the airfoil self-noise. Comparing the blade elements with a local radius of 0.875 m in the HAWT and VAWT conditions the predicted sound pressure levels are the 78.5 dB and 89.8 dB respectively. In case of the HAWT with predicted local angle of attack ranging from 2.98º to 4.63º, the acoustic spectrum will vary primarily within broadband frequency band 1.74–20 kHz. For the VAWT with the local angle of attack ranging from 4º to 20º the acoustic spectrum varies within low and broadband frequency bands 2 Hz – 20 kHz.
    Źródło:
    Archives of Acoustics; 2017, 42, 1; 83-91
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Transonic flows, shock wave-turbulent boundary layer interaction
    Autorzy:
    Doerffer, P.
    Kaczyński, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1953982.pdf
    Data publikacji:
    1998
    Wydawca:
    Politechnika Gdańska
    Tematy:
    transonic flows
    shock waves
    turbulent boundary layer interaction
    computational fluid dynamics CFD
    CFD
    flow configurations
    profile flow
    helicopter rotor
    hovering
    forward flight
    internal flows
    Opis:
    Shock wave-boundary layer interaction is one of the most important phenomenon in transonic flows. Due to its complexity it is difficult as well for experimental as for numerical study. The growing potential of CFD is therefore of great importance. Different aspects of shock wave-boundary layer interaction should be studied in different flow configurations. Therefore results concerning profile flow, helicopter rotor at hovering and forward flight and internal flows are presented in this paper. These are to illustrate our ability in CFD in general. Besides flow simulation the development of codes is carried out.
    Źródło:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 1998, 2, 2; 271-286
    1428-6394
    Pojawia się w:
    TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Prediction of laminar-to-turbulent transition in a separated boundary layer subjected to an external acoustic forcing
    Autorzy:
    Kubacki, S.
    Rarata, Z.
    Drózdz, A.
    Gnatowska, R.
    Sokolenko, V.
    Elsner, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/38697107.pdf
    Data publikacji:
    2023
    Wydawca:
    Instytut Podstawowych Problemów Techniki PAN
    Tematy:
    laminar-to-turbulent transition
    separated boundary layer
    acoustic excitation
    algebraic intermittency model
    Opis:
    The new Reynolds-averaged Navier–Stokes (RANS)-based method has been developed for taking into account, in an approximate manner, the effect of external acoustic forcing on laminar-to-turbulent transition in a separated boundary layer. Experimental studies [33] report an increase of the turbulent shear stress within the separated boundary layer under the influence of acoustic forcing. Enhancement of flow disturbances in a reversed flow region was also reported in our experiment. Experimental findings stimulated the development of a reduced-order aero-acoustic strategy. The effect of acoustic forcing was incorporated into the modelling framework of an algebraic intermittency model. The model component was tuned based on our experimental data and validated on reference experiments. The results show the feasibility of the proposed model to simulate flow over a flat plate and the NACA0018 profile.
    Źródło:
    Archives of Mechanics; 2023, 75, 5; 591-616
    0373-2029
    Pojawia się w:
    Archives of Mechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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