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난류 와류의 입사에 의한 이차원 평판 에어포일 캐스케이드의 광대역 소음장의 계산
정철웅(Cheong, Cheolung),죠셉필립(Joseph, Phillip),이수갑(Lee, Soogab) 한국소음진동공학회 2005 한국소음진동공학회 논문집 Vol.15 No.6
Acoustic power spectrum of the upstream and downstream sound field due to an isotropic frozen turbulent gust impinging on a cascade of flat plate airfoils are computed by using a analytic formulation derived from Smith's method, and Whitehead's LINSUB codes. A parametric study of the effects on sound power of the number of blades and turbulence length scale is performed with an emphasis on analyzing the characteristics of sound power spectrum. Through the comparison of the computed results of sound power, it is found that acoustic power spectrum from the 2-D cascade subject to a ingested turbulence can be categorized into two distinct regions. one is lower frequency region where some spectral components of turbulence do not contribute to the cut-on acoustic modes and therefore the effect of the cascade geometry is more dominant ; the other is higher frequency region where all of spectral components of turbulence make contributions to cut-on acoustic modes and thus acoustic power is approximately proportional to the blade number.
평판 에어포일 캐스케이드와 입사 난류의 상호작용에 의한 광대역 소음의 모달 음향 파워 특성
정철웅(Cheong, Cheol-Ung),쥬딕 빈센트(Jurdic, Vincent),죠셉 필립(Joseph, Phillip) 한국소음진동공학회 2008 한국소음진동공학회 논문집 Vol.18 No.1
This paper investigates the modal acoustic power by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. Basic formulation for the acoustic power upstream and downstream is based on the analytical theory of Smith and its generalization due to Cheong et al. The acoustic power spectrum has been expressed as the sum of cut-on acoustic modes, whose modal power is the product of three terms: a turbulence series, an upstream or downstream power factor and an upstream or downstream acoustic response function. The effect of these terms in the modal acoustic power has been examined. For isotropic turbulence gust, the turbulent series are only reducing factor of the modal acoustic power. The power factor tends to reduce the modal acoustic power in the upstream direction, although the power factor is liable to increase the modal acoustic power in the downstream direction. The modes close to cut-off are decreasing strongly, especially in the downstream direction. Therefore the modes close to cut-off don't contribute highly to the radiated acoustic power in the downstream direction, although the modal acoustic pressure is high for these modes.