1999 Fiscal Year Final Research Report Summary
Study on the effect of the boundary layer on the generation of aerodynamic noise and its control method.
| Project/Area Number |
09450084
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Fluid engineering
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| Research Institution | NIHON UNIVERSITY |
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Principal Investigator |
FUJITA Hajime College of Science and Technology, NIHON UNIVERSITY, Professor, 理工学部, 教授 (40251673)
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| Co-Investigator(Kenkyū-buntansha) |
ZENDO Yasuo Environmental Engineering Division, Railroad Technical Research Institute, Section Head, 環境工学研究部, 研究室長
SAGAWA Akio Environmental Engineering Division, Railroad Technical Research Institute, Section Head, 環境工学研究部, 研究室長
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| Project Period (FY) |
1997 – 1999
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| Keywords | Aerodynamics Noise / Aeolian Tone / Flow around cylinders / pressure Fluctuation / Karman Vortex |
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| Research Abstract |
Experimental investigations were conducted in order to understand the characteristics of the Aeolian tone generated from two-dimensional square and circular cylinders with pressure transducers embedded on the surface. The following conclusions were obtainec.
1) Square Cylinder
The peak level of the Aeolian tone is maximum when the angle of attack is 0°, or, a flat surface is placed normal to the mean flow. The separated flow from the leading edge corner of the square cylinder reattaches to the side surface for the angle of attack between 10°to 13°. The surface pressure fluctuation becomes minimum at this angle of attack and consequently the Aeolian tone becomes minimum.
2) Circular Cylinder
The characteristics of the Aeolian tone radiated from a circular cylinder can be divided into three categories in the Reynolds number, Re, I.e. sub-critical (Re<3x10ィイD15ィエD1), super critical (3x10ィイD15ィエD1<Re<10ィイD16ィエD1) and trans-critical (Re>10ィイD16ィエD1) regions. In the sub-critical region, the surf
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ace pressure fluctuation is uniform spanwise and the coherence between the Aeolian tone is high and the Strouhal number is 0.2. In the super-critical region, the Strouhal number jumps up to 0.45 and the peak level of the Aeolian tone decreases sharply. The surface pressure fluctuation shows strong three-dimensionality and only a fractional part in spanwise shows high coherence with the Aeolian ire. In the trans-critical region, the Strouhal number returns to 0.2 and the spectra of the surface pressure fluctuation and the Aeolian tone show somewhat random nature with a blunt peak. The comparison between the measured and predicted Aeolian tone level from the surface pressure fluctuation shows good agreement for the sub- and super-critical regions but the predicted level is approximately 10 dB lower than the measured level for the trans-critical region.
3) Reduction of the Aeolian Tone
A half rounded square cylinder shows approximately 10 dB lower Aeolian tone level when the rounded part is faced to the mean flow, compared to the circular cylinder with the same diameter. When a wire of diameter d is wound in spiral with a pitch p,around a circular cylinder of diameter D, the Aeolian tone is considerably decreased when d/D>0.2 and p/D=3. Less
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Research Products
(6 results)
