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題名 | 二維機翼上方已失速流場受到簡振擾動後流場特性之探討=Subharmonic Perturbation on Stall Flow Structure by Oscillating Airfoil at Small Amplitude |
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作 者 | 郭正雄; 李夏吉; | 書刊名 | 力學 |
卷期 | 14:1 1998.06[民87.06] |
頁次 | 頁31-42 |
分類號 | 447.5532 |
關鍵詞 | 相位平均法; 失速後; 雷諾剪應力; 簡諧擾動; Phase-average technique; Post-stall; Reynolds stress; Harmonic perturbation; |
語文 | 中文(Chinese) |
中文摘要 | 本研究是以實驗方法探討NACA0012機翼處於平均攻角為15°度並以剪流層不穩 定波動之次諧和頻率(subharmonic frequency)作簡諧運動時,翼面上方已失速流場結構特 性的變化與雷諾剪應力在不同截面之分布及沿下游方向變化之關聯。當機翼處於輕失速攻角 (light stall angle of attack 15°)時,若選取接近剪流層不穩定波動的次諧和頻率為搖擺頻率 fe,使機翼作小振幅(�b1°)之俯仰運動時,其重要結果如下:(1)將使已失速且由翼前緣 分離的流體重新再附著於翼面,並於較接近翼面處形成一個強度較大且較具組織化的渦漩結 構。(2)上翼表面的靜壓力分布由平緩的高壓狀態變成低壓狀態,顯示其空氣動力特性得以 改善。(3)翼上表面不同的x╱c截面上,雷諾剪應力分布峰值之位置即對應於剪流層的位 置。(4)當剪流層不穩定波動現象仍未產生時,其對應截面上之雷諾剪應力的大小幾乎為零。 當波動振幅漸大時,在對應截面上之雷諾剪應力分佈之峰值逐漸增強:直到當剪流層不穩定 波動最強時,其雷諾剪應力在對應截面上之峰值達到最大值且具有非常集中的分布。(5)當 由翼前緣分離的剪流層重新附著於翼上表面時,在該對應截面上雷諾剪應力分佈的峰值則明 顯減弱:同時,(6)於在附著位置的下游各截面上,剪流層和邊界層交互作用增強,則各截 面上雷諾剪應力的分布逐漸變寬但其峰值幾乎保持不變。在不同截面上,由雷諾剪應力之峰 值及分布寬度之變化,可清楚的了解翼面上方剪流層的演化過程與邊界層交互作用的情形。 |
英文摘要 | Stall flow structure perturbed by oscillating airfoil (NACA0012) at small amplitude (±1°) is investigated by experiment. It is found that the light-stall flow structure can be modified to reattach onto the airfoil surface while the perturbation at the subharmonic frequency of the shear layer instability is applied. Moreover, the magnitude of the mean pressure coefficient becomes more negative leading to strong suction over the upper surface of the airfoil. The peak value of the Reynolds stress increases while the shear layer instability initiates and grows. The broadness of the cross-sectional distribution of the Reynolds stress represents the thickness of the shear layer; whereas the peak-value indicated the stregth of the radial gradient of the streamwise velocity. The cross- sectional distribution is hightly concentrated and the peak-value reaches the maximum near the location where the strength of the shear layer instability is the strongest. The peak-value decreases dramatically at the flow-reattachment location. Downstream of the reattached location, the peak- value of the Reynolds stress remains nearly unchanged; however, the broadness of the cross- sectional profile becomes wider because the continuous interaction of the separated shear layer and the thickened boundary layer. |
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