プレートから放射される空力音に関する研究 : 第2報,弦長と波長の比が発生音の音響特性に及ぼす影響(機械力学,計測,自動制御)

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In order to investigate the characteristics of aerodynamic sound generated from plates which have various chord-to-thickness ratios (=2.0〜37.5) and four types of edge shapes consisting of the semi-circular and square, wind tunnel experiments are conducted. Moreover, the sound source distributions of the aerodynamic sound generated from the plates with the square edges are calculated by the 2-dimensional numerical analysis based on the Lighthill's equation with the incompressible flow data. In this study, some basic characteristics of the aerodynamic sound such as (i) the Peak Strouhal number St, (ii) the increase in Peak SPL with the wind velocity U, (iii) the radiation directivity and (iv) the practical critical condition of acoustically compact for chord-to-sound wave length ratio c/λ, are investigated. As a result, it is found that the St depends on the leading edge shape and that the Peak SPL isn't proportional to U^6 under the condition that c/λ becomes greater than about 0.3 (≒1/π). Moreover, the Lighthill's sound source near the trailing-edge is the main contributor for the sound field independently of the edge shape. This result leads to a simple model which consists of the dipole source and the rigid plate for the acoustic analysis. We can also derive the same critical condition of c/λ from the sound calculation results of the previous model by the 2-dimensional boundary element method.
社団法人日本機械学会の論文
2003-09-25