運用譜本徵正交分解分析擬序結構之渦度力對於NACA0012翼型的影響

Abstract

本研究探討了在攻角為7.5度和10度、雷諾數為50,000的條件下，擬序結構在NACA0012上氣動力之影響。使用譜本徵正交分解(SPOD)演算法識別擬序結構，並利用力元理論量化其對阻力和升力的影響。在7.5度攻角下，第一個SPOD模態的第零個頻率對應的流場為一遵循再附著流(reattachment flow)軌跡之近牆流動(near-wall stream)，而第一個頻率則對應於在流場重新附著的位置處所形成的逆時針渦旋對。第一個SPOD模態的第二頻率對應於在源於重新附著點(reattachment point)附近的剪切層中較小的逆時針渦旋對。在攻角為10度時，第一個SPOD模態的第零個頻率具有一個大型漩渦結構，它在翼型的上半部產生強烈的流動，對阻力和升力會產生重要影響。第一個SPOD模態的第一個頻率代表一個非對稱的渦旋對，而第二個頻率則由一系列控制前緣分離的渦旋對所組成。最後，在第二個SPOD模態的第零個頻率，翼型尾緣附近的順時針前緣分離渦旋對對阻力產生正貢獻，而逆時針前緣分離渦旋對對阻力產生負貢獻。本研究結果表明，擬序結構對於NACA0012翼型產生的氣動力力有顯著影響並且可使用SPOD演算法和力元理論有效地進行識別和量化。

The present study investigated the aerodynamic forces exerted by coherent structures on the NACA0012 airfoil at two different angles of attack (AoA=7.5 and AoA=10) and a chord-based Reynolds number of 50,000. The spectral proper orthogonal decomposition (SPOD) algorithm was employed to identify the coherent structures, and the force representation theory was used to quantify their impact on drag and lift forces. At an angle of attack of 7.5 degrees, the zeroth frequency of the first mode corresponded to an oscillating near-wall stream that follows the reattachment flow pattern, while the first frequency corresponded to a counter-rotating vortex pair originating where the flow reattaches. The second frequency of the first mode corresponded to smaller counter-rotating vortex pairs at the shear layer originated near the reattachment point. At an angle of attack of 10 degrees, the zeroth frequency of the first SPOD mode was found to have a large vortex structure that causes a strong flow along the suction side of the airfoil and results in a significant impact on drag and lift forces. The first frequency of the first SPOD mode represented an asymmetric vortex pair, while the second frequency of the first SPOD mode consisted of a series of vortex pairs that determine the leading-edge separation. Finally, for the zeroth frequency of the second SPOD mode, a clockwise primary LEV near the trailing edge of the airfoil provided a positive contribution to drag, while a counterclockwise LEV provided a negative contribution. The findings suggest that coherent structures have a significant impact on the aerodynamic forces exerted on airfoils and can be effectively identified and quantified using the SPOD algorithm and force element theory.