2004 Fiscal Year Final Research Report Summary
Investigation on the velocity field near the ground during downburst impingement
| Project/Area Number |
15560152
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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 | Keio University |
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Principal Investigator |
MASUDA Shigeaki Keio University, Faculty of Science and Technology, Professor, 理工学部, 教授 (90051664)
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| Co-Investigator(Kenkyū-buntansha) |
OBI Shinnosuke Keio University, Faculty of Science and Technology, Professor, 理工学部, 教授 (80233609)
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| Project Period (FY) |
2003 – 2004
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| Keywords | downburst / atmospheric turbulence / particle image velocometry / F-factor / vertical gravitational flow / vortex ring / laboratory experiment |
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| Research Abstract |
As a laboratory model of downburst, statistics of turbulent velocity field of a vertical gravitational flow is investigated. By mechanically breaking a thin film fixed at the bottom of a cylindrical container, a finite mass of a high-density liquid begins to fall into a stationary low-density liquid, forming a vertical thermal, impinging onto a horizontal ground and diverging radially outward. Taking care of keeping high reproducibility, the ensemble average was performed over hundred samples employing PIV. The ensemble-averaged maps of velocity vectors, azimuthal vorticity and turbulent stresses in a meridian plane are obtained. Based on them, the statistical characteristics in the downdraft stage, impinging stage and diverging stage are examined. The nature and the role of the circulatory flow are demonstrated. It was revealed that the associated circulatory flow is not the result of rolling-up of the shear layer at the boundary of the high density parcel, but it is purely inviscid and well described by Hill's vortex theory. The results shows reasonable agreement with the real downburst observed in the atmosphere. Based on these results, the degree of risk for aircraft encountering a downburst is evaluated.
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Research Products
(2 results)
