三維接合面馬蹄渦抑制研究

THE SUPRESSION OF THREE-DIMENSIONAL JUNCTURE HORSESHOE VORTEX

接面流為一複雜的三維流場現象，發生於突起的障礙物與平面交界處，當入流通過接面處時，邊界層會開始增厚並產生逆壓梯度，此現象會造成流場的剝離，而且生成一渦系包覆於結構物兩旁，這種現象有如馬蹄鐵的樣子，故又稱作馬蹄渦。在許多的工程應用上，突起物是極為常見的結構特徵，然而，接面流現象給工程帶來了許多不利的影響，例如結構物上游的淘刷或下游的振動噪音現象。本文中，我們利用RANS方法與Spalart-Allmaras紊流模型，了解紊流場中的接面流會產生之物理現象，幾何模型為平板上之有限翼，以翼型弦長作為基準，此流場的雷諾數約為。在結果中，我們捕捉到了馬蹄渦的結構以及不均勻尾跡流的現象，透過整流罩（fairing）幾何，我們希冀對流場的發展帶來正面的效應。在這裡，透過CAD軟體將導流片及整流罩的形狀因子加以參數化，探討不同無因次長度、無因次高度以及不同曲率的幾何，其對於此流場的改變。最後發現：加裝適當的整流罩後，前緣的馬蹄渦強度能大幅地減弱。然而，整流罩的使用會使尾流場的不均勻程度提高，並且使阻力增加。

Junction flow occurs when a flow encounters a three-dimensional appendage-body junction. It is a complicated physical phe-nomenon. The boundary layer becomes thicker as the inflow passes the obstacle. The flow separates upstream of the body due to an adverse pressure gradient. Then the vortex system wrapping around the configuration is formed, which is named horseshoe vortex. Many engineering applications associated with appendage-body junction will cause some undesirable effects, such as scour-ing hole around a pier or acoustic noise of far-field wake. We used the Reynolds-averaged Navier-Stokes (RANS) equations, and the Spalart-Allmaras turbulence model for study-ing the phenomenon. The model of the wing/flat-plate was employed. Basically, the main flow features are captured in the simula-tion. We can observe the leading-edge horseshoe vortex and the non-uniformity of the far-field wake. Some simple configurations on the wing like fairing is a way to control the flow separation. The shape of the fairing was studied parametrically by using the CAD software. We conducted the simulation by changing three relevant parameters of the fairing, including the non-dimensional length and non-dimensional height. At last, we found that with a proper fairing, the leading-edge horseshoe vortex could be sup-pressed. However, the wake distortion was not eliminated completely by adding the fairing, and the drag grown as the parameters increased.