2001 Fiscal Year Final Research Report Summary
Interactive control of Unsteady separation Research Based on of a Precursor of Separation
| Project/Area Number |
11305016
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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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 | HOKKAIDO UNIVERSITY |
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Principal Investigator |
MOCHIZUKI Osamu Hokkaido Univ. Grad. School of Eng., Asso. Prof., 大学院・工学研究科, 助教授 (50157830)
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| Co-Investigator(Kenkyū-buntansha) |
KIYA Masaru Kushiro National College of Tech. President, 校長 (50001160)
ISHIKAWA Hitoshi Hokkaido Univ. Grad. School of Eng., Inst., 大学院・工学研究科, 助手 (90311521)
HAYAKAWA Michio Hokkaido Univ. Grad. School of Eng., Inst., 大学院・工学研究科, 助手 (80002038)
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| Project Period (FY) |
1999 – 2001
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| Keywords | Separation / Unsteadiness / Interactive Control / Precursor / Shear Lager / Wake / Vortex Ring / Pitching Aerofoil |
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| Research Abstract |
There are many difficulties to be solved in order to achieve a method for preventing separation by means of small energy consumption: prediction of separation, determination of the optimal timing for starting control and a way of saving the total amount of energy required for control. The purpose of this study is to determine the optimal timing for starting control before separation in the saving-energy point of view. The most difficult problem in this stage is to predict separation. To resolve this difficulty, the dynamic stall of an airfoil in pitching-up motion was adopted, because a separation occurred at the same phase during a pitching-up motion if the pitch rate was the same. Thus, since the onset of separation is known in this study, we can search the optimal timing for starting control.
The wall-jet ejected from a thin slit near the leading edge of the airfoil was used to suppress separation, because it is easy to estimate the amount of energy to prevent separation. Many combin
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ations of the timing of ejection and velocity of the wall-jet were tested to determine the least amount of energy required to suppress the stall. It was found that, within the limits of our experimental conditions, there exists an optimum combination.
To start control before separation occurs is of great advantage to a saving energy for suppression of separation compared with the control starting after separation occurs. It was found that, within the limits of our experimental conditions, the optimum non-dimensional time to start control was 2 just before separation. This indicates that we should find a precursor signal of separation before that time.
The precursor of separation was investigated by observation of the process of separation controlled in a two-dimensional diffuser. Surface pressure fluctuation with a particular frequency appears and is amplified exponentially before separation occurs. This is the cause of the inflectional instability of the velocity profile that occurs before separation. We conclude that this signal can be regarded as a precursor of separation. Less
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Research Products
(22 results)
