1998 Fiscal Year Final Research Report Summary
Effect of the shape of roughness elements on admissible roughness of flow passage
| Project/Area Number |
09650207
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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 | Kanagawa Institute of Technology |
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Principal Investigator |
AKAIKE Shiro Kanagawa Institute of Technology, Factory of engineering, President, 工学部, 学長 (50017919)
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| Co-Investigator(Kenkyū-buntansha) |
NEMOTO Mitsumasa Kanagawa Institute of Technology, Factory of engineering, Research Associate, 工学部, 助手 (90085134)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Boundary layer / Admissible roughness / Roughness element / Transition / Friction loss |
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| Research Abstract |
Although it is necessary to finish the passage wall to be a hydraulically smooth, in order to reduce a friction loss in flow passage, to finish the wall beyond an admissible roughness is useless and then expensive. Therefore, it needs to know the admissible roughness correctly. This study intends to clarify the effect of the shape of roughness elements on the admissible roughness of flow passage.
It is known that the transition from a smooth to rough surface occurs, when the roughness elements which protrude, reach outside the viscous sublayer. The transition for the roughness elements with cavity type, however, has not been clear. Therefore, two experiment for the roughness elements of circular and slit types were performed. For the former, experimental results were presented at the conference of Turbomachinery Society of Japan (11.References) and the friction characteristic in transition regime of rough wall passage was made clear.
Latter experiment was carried out by using roughness elements such as rectangular single-slit and multislits at right angles to the flow using an air. The flow passage is a cross-section 500 * 5OOmm and 2750mm long. The velocity and turbulence distributions in a boundary layer over the slits were measured by the hot wire anemometer and discussed in detail. Flow visualization for the flow over the slits was also performed in a water tunnel.
It seems that the flow transition from a smooth to a rough surface of shallow slit tested is earlier than that of the deep slits. Therefore, when the roughness elements consist of a shape of slits, the transition does not determine by the depth of slit, so that the determination of the admissible roughness has to take care the shape of roughness elements.
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