激波控制鼓包对跨声速抖振影响的数值研究

Numerical study on impact of shock control bump on transonic buffet

在跨声速飞行时,激波控制鼓包不仅能够减弱机翼上表面的激波强度从而降低波阻,对跨声速抖振也有一定的改善作用。通过URANS方法数值模拟来探究二维激波控制鼓包对OAT15A超临界翼型跨声速抖振性能的影响规律,并研究以巡航设计点减阻与抖振状态减振2种目标设计的鼓包的区别。以巡航设计点减阻优化设计出的鼓包,在抖振条件下,能够推迟了翼型上表面的压力恢复,减弱了激波与边界层的相互干扰作用,达到减弱抖振幅度的效果,然而不能对抖振实现完全抑制。通过改变鼓包相对位置、高度和长度计算得到鼓包参数对抖振的影响规律,分析典型流场得到鼓包抑制抖振现象的工作机理是:鼓包减弱了激波强度的同时,阻碍了鼓包尾部边界层向上游移动与激波相互干扰,从而稳定了激波抖振现象。另外,基于巡航设计点减阻设计的2个鼓包相对参考位置距离分别为0.04c和0.10c(c为翼型弦长),与同等高度鼓包在抖振状态完全抑制抖振且不降低升力的位置范围的[-0.01,0.02]c和[0.01,0.08]c不同,二者位置最小相差0.02c,而鼓包这段距离差异对巡航特性和抖振性能都有着重要影响作用。总而言之,以巡航设计点减阻与抖振状态减振2种目标设计得到鼓包位置上存在偏差,工程设计中应当综合考虑在二者中做出权衡取舍,才能设计出综合性能更好的激波控制鼓包来提升翼型的跨声速性能。

The Shock wave Control Bump(SCB) can effectively weaken the shock wave intensity of the airfoil at transonic speeds, meanwhile exerting a positive effect on transonic buffet control. In this study, the URANS method is applied to numerical simulation to explore the control effect of the 2 D SCB on the OAT15 A supercritical airfoil under the transonic buffet condition. The differences between the two goals of drag reduction and buffet control are further investigated. Two bumps are designed with drag reduction optimization at cruise design points. Under the buffet condition, the bumps delayed the pressure recovery on the upper surface of the airfoil and weakened the interaction between the shock wave and the boundary layer. Therefore, the pressure fluctuation amplitude of bump configurations is reduced despite incomplete suppression of the buffet. Then, the effect of the bump crest position, height and length on the buffet is studied. The working mechanism of the SCB to suppress the buffet is obtained by analyzing the typical flow field. The bump reduced the shock wave intensity, preventing the boundary layer at the rear of the bump from moving upstream and interfering with the shock wave, resulting in shock buffet suppression. Based on the drag reduction design at the cruise design point, the relative reference positions of the two bumps are 0.04c and 0.10c(c representing length of the chord), respectively. The position range of the bumps at the same height to completely suppress the buffet without reducing the lift are [-0.01, 0.02]c and [0.01, 0.08]c, respectively. The smallest variation of the bump location between drag reduction and shock buffet control is 0.02c, and this distance has a significant impact on cruise characteristics and buffet performance of the airfoil. Consequently, the two types of bumps designed based on drag reduction at the cruise points and buffet control under the buffet condition have different crest positions. In engineering design, a trade-off between the two design goals should be achieved in bump design by comprehensive consideration to improve the overall performance of airfoils under transonic flight conditions.