2003 Fiscal Year Final Research Report Summary
Effects of Pressure Gradient on Heat Transfer in Turbulent Boundary Layer
| Project/Area Number |
13450083
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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 |
Thermal engineering
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| Research Institution | Nagoya Institute of Technology |
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Principal Investigator |
NAGANO Yasutaka Nagoya Institute of Technology, Department of Environmental Technology, Professor, 工学研究科, 教授 (20024325)
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| Co-Investigator(Kenkyū-buntansha) |
HOURA Tomoya Nagoya Institute of Technology, Department of Environmental Technology, Research Associate, 工学研究科, 助手 (00324484)
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| Project Period (FY) |
2001 – 2003
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| Keywords | Turbulent Boundary Layer / Adverse Pressure Gradient / Measurement / Forced Convection / Heat Transfer / Temperature Fluctuation / Turbulent Heat Flux |
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| Research Abstract |
An experimental investigation has been conducted on non-equilibrium turbulent boundary layers subjected to adverse pressure gradients (APGs), developing on the uniformly heated flat wall.
The conclusions are as follows :
(1) In the APG boundary layer, the Stanton number follows the correlation curve for a flat plate, although the skin friction coefficient decreases drastically, in comparison with ZPG flow. The temperature profiles in APG flows lie below the conventional thermal law of the wall in the fully turbulent region. Moreover, turbulent Prandt1 number decreases in the fully turbulent region. These findings indicate that heat transfer is greatly enhanced under the APG conditions, i.e., the eddy diffusivity for heat becoming much larger than that for momentum.
(2) R.m.s. intensities of temperature fluctuation in the APG flows remain unchanged, in comparison with the ZPG flow. This should indicate that the wall-normal fluctuation, which remains unchanged in the APG flow, definitely co
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ntrols the heat transfer from the wall even in complex flows. Higher-order moments and p.d.f.s of temperature fluctuations are not greatly affected in the near wall region by imposing APG.
(3) The quadrant splitting and trajectory analyses reveal that the effects of APG on the thermal field are not similar to that on the velocity field. Both the ejection-and sweep-motions contribute significantly to the heat transport in the APG flow, though the sweep motions whose durations become shorter are the main contributors to the momentum transfer.
(4) In the APG boundary layer, the momentum and heat transfers occur in the direction toward the wall from the region away from the wall. The structural change in APG flow causes the non-local interactions between the temperature fluctuations and the wall-normal motions. However, the situation is fairly complex because the heat transport is mainly determined by the ejection motions, which are not significant contributors to the momentum transport in the APG flow. Less
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