• Title/Summary/Keyword: Vortex center

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Numerical Investigation of Flow-pattern and Flow-induced Noise for Two Staggered Circular Cylinders in Cross-flow by LBM

  • Kim, Jeong-Whan;Oh, Sae-Kyung;Kang, Ho-Keun
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.1
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    • pp.82-93
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    • 2008

  • The flowfield behind two cylinders and flow-induced noise generated from the cylinders in various arrangement are numerically investigated based on the finite difference lattice Boltzmann model with 21 velocity bits. which is introduced a flexible specific heat ${\gamma}$ to simulate diatomic gases like air. In an isolated cylinder with two type of mesh. some flow parameters such as Strouhal number $S_t$ and acoustic pressure ${\Delta}p$ simulated from the solution are given and quantitatively compared with those provided the previous works. The effects of the center-to-center pitch ratio $L_{cc}/d=2.0$ in staggered circular cylinders as shown in Fig. 1 and angles of incidence ${\alpha}=30^{\circ}(T_{cc}/d=0.5)$, $45^{\circ}(T_{cc}/d =0.707)$ and $60^{\circ}\;(T_{cc}/d=0.866)$, respectively, are studied. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in staggered arrangement. With the results of drag $C_d$ and lift $C_l$ coefficients and vorticity contours. the mechanisms of the interference phenomenon and its interaction with the two-dimensional vortical structures are present in the flowfields under $Re\;{\le}\;200$. The results show that we successively capture very small pressure fluctuations, with the same frequency of vortex shedding, much smaller than the whole pressure fluctuation around pairs of circular cylinders. The upstream cylinder behaves like an isolated single cylinder, while the downstream one experiences wake-induced flutter. It is expected that, therefore, the relative position of the downstream cylinder has significant effects on the flow-induce noise, hydrodynamic force and vortex shedding characteristics of the cylinders.

  • https://doi.org/10.5916/jkosme.2008.32.1.82 인용 PDF KSCI

Noise Source of Large Wind Turbine (대형 풍력발전기 소음원 분석)

  • Shin, Hyung-Ki;Bang, Hyung-Jun
    • Journal of Environmental Science International
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    • v.18 no.8
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    • pp.927-932
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    • 2009

  • Wind turbine noise become main environmental problem as wind energy have been installed all around. Noise from large wind turbine give annoyance to listener, moreover it increase loading to whole system by restricting blade tip speed. However accurate noise mechanism of wind turbine is not yet examined. This paper reviewed noise source and analysis theory. Broadband noise if main component of wind turbine noise and airfoil self noise is main noise source. These make acoustic analogy hard to apply for analysis. For this reason, experimental equation is method for wind turbine noise prediction up to now. Spectrum analysis shows that vortex shedding noise exists around $1k{\sim}2k$ Hz. This region is most sensitive frequency range to human. Thus it is necessary to reduce this noise source.

  • https://doi.org/10.5322/JES.2009.18.8.927 인용 PDF KSCI