圆柱附加旋转整流罩表面压力分布及气动力特性

Pressure Distribution and Aerodynamics of Circular Cylinder with Freely Rotating Fairings

对圆柱附加固定整流罩的已有研究表明,它在降低升阻力和抑制涡激振动方面有优良的效果。但固定整流罩具有方向敏感性,当来流方向改变后效果会受到显著影响,甚至起到增加升阻力和加剧涡激振动的反作用。本文给圆柱附加了圆弧直径为40mm,形状夹角α分别为30°、45°、60°、75°和90°五种尺寸的旋转整流罩,并进行了风洞实验。其中整流罩可以自由地围绕圆柱轴线旋转。实验结果表明:旋转整流罩在流体力产生的力矩作用下,旋转至一个偏离尾流中心线固定角度的动态平衡位置,而平衡位置偏转角δ随着形状夹角α的增大而增大。附加旋转整流罩后,相对单圆柱能够提高尾迹区域压力,并能使时均阻力和脉动升力分别在α=30°和α=75°时获得最大43.5%和67.0%的降低。此外,对于小α(α≤60°)情况,漩涡脱落频率明显高于单圆柱情况,而对于大α(α≥75°)情况,则与单圆柱情况相接近。所有旋转整流罩升力主频的幅值较之单圆柱有了很大程度的降低,可见旋转整流罩在抑制漩涡脱落方面有很好的效果。

Previous study of flow around a cylinder with fixed fairing shows that it exhibits excellent effect on drag and lift reduction and vortex-induced vibration suppression. But fixed fairing is sensitive to flow derection. When inflow direction changes, its effect may not only be reduced hut present retroaction, that is drag and lift are increased and vortex-induced vibration intensified. In present study, a rotating fairing with diameter D （40 mm） and five different shape angle a （30°, 45°, 60°, 75° and 90° respectively） was designed, and wind tunnel test for the fairing was carried out. This fairing can freely rotate around cylinder axis. Experimental results show that the fairing may rotate around an off-axis deviated from the centerline of the wake which forms an equilibrium angle 8 （on either side of wake） due to integrated effect of pressure difference along either side of fairing. Off-axis angle increases continuously with the increase of angle a, and reachs its maximum value 62° when a = 90°. Furthermore, it is concluded that both mean drag coefficient and root-mean-square fluctuating lift coefficient, that are largely determined by equilibrium angle, are less than that of corresponding bare cylinder and the reduction up to about 43.5% and 67.0% was obtained, respectively. In addition, for small a （a≤60°）,vortex shedding frequency has a significant increase compared with bare cylinder. But for large a （a≥ 75°） , the situation is almost similar to bare cylinder. The peak values of rotating fairing are much lower than that of bare cylinder, which indicates that the vortex shedding is suppressed significantly.