1998 Fiscal Year Final Research Report Summary
DRAG REDUCTION OF NEWTONIAN FLUIDS WITH FLUID SLIP
| Project/Area Number |
09450082
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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 | TOKYO METROPOLITAN UNIVERSITY |
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Principal Investigator |
WATANABE Keizo TOKYO METROPOLITAN UNIVERSITY,PROFESSOR, 大学院・工学研究科・機械工学専攻, 教授 (20072134)
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| Co-Investigator(Kenkyū-buntansha) |
MIZUNUMA Hiroshi TOKYO METROPOLITAN UNIVERSITY,ASSOCIATE PROFESSOR, 大学院・工学研究科, 助教授 (20117724)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Fluid Mechanic / Newtonian Fluids / non-Newtonian Fluids / Circular Pipe / Enclosed Rotating Disk / Circular Cylinder / Fluid Slip / Drag Reduction / Highly Water-Repeellent Wall |
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| Research Abstract |
There have been few studies conducted on laminar drag reduction, although many studies have been performed on drag reduction for turbulence modification, which is achieved by adding a high molecular polymer of surfactant. We clarified laminar drag reduction for Newtonian fluids in a circular pipe, an enclosed rotating disk and a circular cylinder with a highly water-repellent wall, in which fluid slip occurs at the wall surface. The results are summarized as follows,
(1) The laminar drag reduction ratio for tap water flowing in a 12-diameter mm pipe, is about 14% and it increases with increasing viscosity
(2) Values obtained using the analytical results agree well with the experimental results for the friction factor and the velocity profile of Newtonian fluids and a power law fluid in a circular pipe.
(3) The wall shear stress is proportional to the slip velocity, and the sliding coefficient depends directly on not only the properties of solid boundary and the fluid but also the characte
… More
ristic length of the flow field.
(4) The frictional moment of the rotating disk with highly water-repellent wall enclosed the chamber in Newtonian fluid was investigated experimentally by means of the torque measurement shaft. The laminar drag reduction in rotating disk flow was found, in which it is about 45% in maximum drag reduction for values of Reynolds number about lO^5.
(5) The flow pattern past a circular cylinder with a highly water-repellent wall was clarified by the flow visualization technique. The calculated result for the streamlines at Re=50 agrees well with the experimental result, and the obtained value of the drag reduction ration was about lO%. It was cleared that the value of the drag coefficient of the circular cylinder with fluid slip is smaller than that of the smooth circular cylinder with no fluid slip because the separation angle increases.
Consequently, the main reasons for the fluid slip are that the molecular attraction between the liquid and the solid surface is reduced because the free surface energy of die solid is very low and the contact area of the liquid is decreased compared with that is the case of a conventional smooth surface because the solid surface has many fine grooves. Less
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