When the vortices shedding from an upstream rod impinge upon the surface of a downstream airfoil, the resultant vortex–body interaction noise can be significant. The use of “natural rod-base blowing” to reduce this interaction noise is investigated numerically using a 3D hybrid computational aeroacoustics approach. The natural blowing is generated through an internal slot that interconnects the stagnation and base region of the rod. Numerical simulation is performed for a straight blowing at blowing rates (BRs) between 6.4% and 16.3% and an oblique blowing with slot–incidence angles ($\theta$) between $0°$ and $15°$, respectively. Far-field noise evaluation demonstrates that the natural rod-base blowing under tested BRs can reduce significantly the noise emission, whereas loses its efficiencies gradually with the increase of angle $\theta$. The most effective case is the straight blowing ($\theta =0°$) at BR$\ge$13.6% where the far-field tonal noise associated with the steady-periodic von Karman vortex shedding is annihilated. The changes in transient flow structures indicate that the natural blowing gradually attenuates the von Karman vortex shedding when BR increases, resulting in a mitigation of vortex–body​ interaction on the airfoil leading surface and hence a reduction of the unsteady lift. At BR=13.6%, as the angle $\theta$ reaches $15°$ from below, a new von Karman vortex street reforms in the flow field, leading to another tonal noise. Linear stability analysis based on a local concept of absolute/convective instability suggests that the absolutely unstable region in the near-wake of the rod elongates first and then shrinks with the increase of BR, while the local absolute growth rate decreases monotonously.

当从上游杆脱落的涡流撞击到下游机翼的表面时，所产生的涡旋体相互作用噪声可能会很大。使用3D混合计算航空声学方法，对“自然杆基吹气”的使用减少了这种相互作用的噪声进行了数值研究。自然吹气是通过内部狭槽产生的，该内部狭槽将杆的停滞和基部区域互连起来。对以6.4％到16.3％的吹气率（BRs）进行的直吹和具有缝隙入射角的斜吹进行了数值模拟（$\theta$）之间 $0°$ 和 $15°$， 分别。远场噪声评估表明，在测试的BR s下自然杆基吹气可以显着降低噪声发射，而随着角度的增加逐渐降低其效率$\theta$。最有效的情况是直吹（$\theta =0°$），BR$\ge$13.6％的噪声与稳定周期的von Karman涡旋脱落有关的远场色调噪声被消除了。瞬态流动结构的变化表明，当BR增加时，自然吹气逐渐减弱了von Karman涡流的散发，从而减轻了翼型前表面上涡流与物体之间的相互作用，从而减少了不稳定升力。在BR = 13.6％，作为角度$\theta$ 到达 $15°$从下方开始，流场中发生了新的冯·卡曼（von Karman）涡街改革，导致了另一种音调噪音。基于局部绝对/对流不稳定性概念的线性稳定性分析表明，杆的近尾迹中的绝对不稳定区域随着BR的增加先伸长然后收缩，而局部绝对增长率单调降低。