1996 Fiscal Year Final Research Report Summary
Comparative Study of Turbulent Coherent Structures Educed by Wavelet Transform, Proper Orthogonal Decomposition and Conditional Averaging
| Project/Area Number |
07455078
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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 | HOKKAIDO UNIVERSITY |
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Principal Investigator |
KIYA Masaru Hokkaido Univ., Fac.of Eng., Prof., 工学部, 教授 (50001160)
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| Co-Investigator(Kenkyū-buntansha) |
IDO Yasushi Hokkaido University, Fac.of Eng., Instructor, 工学部, 助手 (40221775)
MOCHIZUKI Osamu Hokkaido Univ., Fac.of Eng., Assoc.Prof., 工学部, 助教授 (50157830)
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| Project Period (FY) |
1995 – 1996
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| Keywords | Fluid Mechanics / Turbulence / Coherent Structure / Modulation / Wavelet Transform / POD / Mixing Layr / Wake |
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| Research Abstract |
Coherent structures in turbulent shear flows have low-frequency modulations. In this study the coherent structure in a turbulent plane mixing layr and its low-frequency modulation are studied by the proper orthogonal decomposition and the wavelet transform. The low-frequency modulation of the coherent structure is also studied for a turbulent plane wake in a region where the turbulent Karman vortex street prevails. Moreover, the extent to which the two methods are effective in educing the coherent structures are discussed. Main results may be summarized as follows.
[1] The fundamental property of the coherent structure in the mixing layr can be represented by the first eigenfunction of the proper orthogonal decomposition. The first eigenvalue occupies 52% of the total kinetic energy.
[2] The proper orthogonal decomposition fails to extract that coherent nature of the velocity fluctuations in the central part of the mixing layr which is due to coherent structure. On the other hand, the wavelet transform does extract the coherent nature of the velocity fluctuations. This is expected to be always the case for velocity fluctuations whose power spectrum has a significant peak associated with the coherent structures.
[3] The coherent structure in the plane mixing layr experiences a large-scale modulation whose wavelength is approximately six times its wavelength. The modulus of the complex Morlet wavelet transform is found to be effective in obtaining this information.
[4] The vortices in the Karman vortex street in the wake experiences a large-scale modulation whose wavelenth is approximately twenty-five times the wavelength of the vortex street.
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