AN EXPERIMENTAL STUDY ON 1/f^<tx> STRUCTRE AND ENTRAINMENT IN TURBULENT BOUNDARY LAYER
| Project/Area Number |
13650182
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | Yamaguchi University |
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Principal Investigator |
MOCHIZUKI Shinsuke YAMAGUCHI UNIVERSITY, Mechanical Eng., Associate professor, 工学部, 助教授 (70190957)
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| Co-Investigator(Kenkyū-buntansha) |
KAMEDA Takatsugu YAMAGUCHI UNIVERSITY, Mechanical Eng., Research Assistant, 工学部, 助手 (70304491)
OSAKA Hideo YAMAGUCHI UNIVERSITY, Mechanical Eng., Professor, 工学部, 教授 (90024611)
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| Project Period (FY) |
2001 – 2002
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| Project Status |
Completed (Fiscal Year 2002)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2001: ¥2,800,000 (Direct Cost: ¥2,800,000)
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| Keywords | Turbulent Boundary Layer / Entrainment / Coherent Structure / Fractals / Equilibrium Boundary Layer |
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| Research Abstract |
In the present study, entrainment mechanisms associated with large scale eddies in turbulent boundary layers has been investigated in terms of 1/f^<tx> intermittent nature defined in fractals. The experiment has been made in a flat plate boundary layer and a self-preserving boundary layer developed under power-law variation of the free-stream. The free-stream is decelerating with x^<-0.188> for the self-preserving boundary layer, thus the boundary layer is subjected to a mild adverse pressure gradient.
A new direct measurement device for the local wall shear stress has been developed and applied in the present experimental study. The measurement device has 20mm circular friction surface and zero-displacement circuit that keeps the floating element at initial position. Application of the new device to the flat plate boundary layer proves that the wall shear stress can be obtained experimentally with sufficiently high accuracy and reliability.
In both the boundary layers, the mean velocity profile near the wall can be reasonably expressed in the logarithmic mean velocity profile with Karman constant of 0.41 and additive constant of 5.0. Strength of wake component in the outer layer mean velocity profile is strongly enlarged by the adverse pressure gradient. The triple velocity products, which mean turbulence diffusion of Reynolds shear stresses and turbulent intensity, become greater in magnitude of absolute values.
The outer layer intermittent nature has been investigated by conditional sampling technique that is applied to recognize turbulent and non-turbulent zones. Two-point double velocity correlation functions were calculated for turbulent zone and non-turbulent zone, respectively. A large scale streamwise vortical motion is expected in turbulent bulge and spanwise size of the vortical motion is squeezed by the adverse pressure gradient. The probability of streamwise interval of turbulent can be successfully explained by power-law functions.
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Report
(3 results)
Research Products
(18 results)
