自1947年10月14日耶格尔驾驶贝尔X-1突破音障, 实现第一次载人超声速飞行以来, 超声速飞行技术已经取得了巨大成就。A-12/SR-71成为第一种以马赫数3巡航飞行的实用飞行器。2004年11月16日, X-43A试验飞行器首次实现了约马赫数10的吸气式巡航飞行, 标志着吸气式高超声速飞行取得了重大进展。相比航天和军用航空领域, 民用航空领域的超声速飞行一直处于进展缓慢的状态, 两种实用的超声速客机图-144和协和在短暂的辉煌之后已经退出了历史舞台(图1, 图2)。究其原因就是当前超声速飞机很差的燃油效率导致的高运营成本以及超声速飞行所带来的声爆两大问题没有得到解决。而这两个问题背后的主要因素都是超声速飞行时产生的强激波。如何减弱超声速巡航飞行时的激波一直是空气动力学家的努力方向。
图1
图2
1935年, 在罗马召开的第五届雅尔塔会议上, 普朗特的弟子, 德国空气动力学家布兹曼(Busemann)[1]首次提出了超声速双翼机的概念(图3)。其基本思想为利用平行放置的两个机翼产生的波系对消, 达到减弱或完全消除超声速飞行时产生的强激波, 进而大幅减小激波阻力的目的。由于当时人类尚未实现超声速飞行, 因此该论文没有得到太多关注。在超声速飞行的早期, 一些著名空气动力学家对这一概念进行了初步的理论研究和实验验证。由于超声速双翼机构型具有更小的阻力、更弱的声爆, 进而具有更好的经济性和环境友好性, 因此有望成为未来超声速运输机的可用形式。近年来, 随着人们对超声速商业飞行的热切期盼, 这一概念重新回到空气动力学家和航空工程师的视野中。纵观历史,超声速双翼机的研究历程可大致分为三个阶段：
第一阶段：1930s, 概念提出阶段, 布兹曼在理论研究的基础上提出了布兹曼双翼机的概念, 但未获太多关注。
图3
1 超声速双翼机的原理
1.1 激波减弱效应
根据超声速线化理论, 无黏、小攻角情况下平板翼型的升力和阻力系数可写为
式中$\alpha $为攻角, $M_\infty $为来流马赫数。
考察由两个平板翼组成的双翼构型, 忽略两个平板翼之间的干扰, 如图4所示。由式(1)和式(2)易得：与单翼构型升力相等时, 双翼构型的攻角为单翼构型的1/2。进而, 双翼构型的阻力系数为单翼构型的1/2(平板相对厚度为零, 即由厚度导致的波阻忽略不计)。即, 产生相同升力的情况下, 双翼构型比单翼构型产生的激波大幅减弱了, 进而减小了升致波阻。
图4
1.2 激波消除效应
超声速双翼机真正的意义在于显著减小甚至消除由厚度产生的波阻。如图5所示, 将传统的超声速菱形单翼从弦线分为相同的两半, 再翻转对称放置, 便形成了典型的布兹曼双翼构型。通过调节上下翼面的相对位置, 使前缘产生的激波刚好打到另一侧机翼的肩点上, 并与该处产生的膨胀波干涉, 从而减弱(消除)激波。理论上, 在设计马赫数下可以完全消除激波, 而由厚度(容积)导致的波阻为零。
图5
1.3 布兹曼双翼机的发展————利歇尔双翼机
利歇尔双翼同时应用了平板双翼的激波减弱效应和布兹曼双翼的激波消除效应, 研究结果表明, 其波阻力为相同升力下平板翼型的2/3。
图6
2 超声速双翼机基本问题研究进展
2.1 非设计点特性
图7
图8
图9
与超声速进气道类似, 超声速双翼构型减速过程的流场往往与加速过程不重合, 存在迟滞现象, 如图10所示。
图10
图11
图12
图13
图14
图15
2.2 三维问题
图16
图17
图18
图19
3 超声速双翼机的工程应用
由于超声速双翼构型具有更小的阻力、更弱的声爆, 进而具有更好的经济性和环境友好性,因此有望成为未来超声速运输机的可用形式。在超声速双翼机从原理向工程转化方面, 日本和美国走在了前列。
图20
2008年, 日本东北大学的楠瀬课题组提出了基于超声速双翼构型的超声速旅客机方案。如图21所示, 整机采用超声速双翼飞翼布局, 四台发动机融合在双翼结构中。客舱在机体顶部, 与机翼融为一体, 双垂尾保证超声速飞行时的稳定性。该方案可将当前东京到纽约的飞行时间减少一半。
图21
图22
图23
通过以上叙述可知, 尽管当前一些研究机构已经开展了超声速双翼机的工程应用研究, 但方案大多停留在纸面上, 概念从理论走向工程实际还有很长的路要走。
4 展望
图24
当前的文献资料中, 还没有对超声速双翼机飞行力学特性以及飞行控制问题研究的报道, 对于工程实用化的飞行器, 飞行力学和飞行控制乃是重中之重, 尤其加速/减速等变模态飞行时的动力学特性与控制问题, 这些也应当是下一步研究工作的重点。楠瀬等在研究中发现, 从亚声速到超声速, 布兹曼双翼的气动中心(焦点)并不像传统机翼一样由约25%移动到约50%弦长, 而是一直维持在25%$\sim$ 27%之间, 预示了良好的操稳特性[14]。除加减速外, 一些常见的机动过程, 如滚转、偏航过程中双翼机构型性能的鲁棒性也是亟待研究的。当前研究结果表明, 壅塞、迟滞等现象可以通过诸如采用前后缘襟翼、机翼变形、前后错动等方式解决。从工程角度来看, 前后缘襟翼方案最为实用, 且前后缘襟翼在起降阶段可以较好地改善飞行器的低速性能。当前研究中, 主要关注超声速双翼构型的超声速性能, 而真实的飞行器需要经历从速度零、高度零加速、爬升至巡航高度进行超声速巡航, 以及减速、下降、着陆等整个历程。研究表明, 目前的超声速双翼构型的低速失速迎角在20度左右, 下一步的研究中需要综合优化包括低速起降、爬升、超声速巡航等各阶段的性能。
对于吸气式超声速巡航飞行器, 其进气道与机体一体化设计也应该为研究重点, 好的一体化设计能在提高气动性能的同时减轻结构重量, 提高有效载荷。当前的文献中还未见相关研究报道。已有方案中,日本东北大学的超声速旅客机进气道设计方案较为理想。
当前公开的文献报道中, 研究重点主要集中于超声速双翼机的超声速减阻问题。然而,当前的研究结果表明, 采用超声速双翼机原理的飞行器虽然波阻较低, 升阻比较高, 但其升力系数普遍偏低, 提高可用升力系数是下一步研究的重点。由于激波的消除效应, 超声速双翼机表现出了优异的低声爆特性, 但当前研究大多集中于满足气动性能后的声爆评估, 对于控制声爆的主动设计报道较少。值得一提的是, 研究人员发现, 双翼构型可以通过合理设置, 将激波反射至天空, 从而减小向地面传播的激波强度, 进而大幅减弱声爆[6], 如图25所示,但代价是降低了升力。因此需要综合考虑升力、阻力、声爆等因素进行设计折中。另外, 双翼的采用大幅增加了飞行器的浸润面积, 在降低波阻的同时增加了摩擦阻力, 需要对各种阻力进行综合优化, 以实现总阻力最低。
图25
对于新概念飞行器来说, 进行缩比模型飞行试验是综合研究气动性能、飞控特性、降低研制风险的重要手段, 工程化过程中可建造缩比超声速双翼机进行模型试飞验证。此外, 超声速双翼机是尖前缘飞行器, 对于长时间巡航飞行, 需要考虑其前缘热防护问题。
总体来说, 超声速双翼机构型已被研究证实为一种有潜力的低波阻、低声爆构型, 有望成为未来超声速巡航飞机的实用构型。但当前的研究主要集中在理论、概念阶段, 工程化还有很长的路要走。虽然存在很多问题, 许多工作亟待开展, 超声速双翼机概念仍然给人们带来了超声速飞行的新希望, 是一种可能出现在未来天空中的低波阻、低声爆构型。
(责任编辑: 胡漫)
参考文献
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A Fundamental study for the development of boomless supersonic transport aircraft
Consideration at off-design conditions of supersonic flows around biplane airfoils
A study of busemann-type biplane for avoiding choked flow
Experimental and computational fluid dynamics around supersonic biplane for sonic-boom reduction
Aerodynamic design of three-dimensional low wave-drag biplanes using inverse problem method
Three-dimensional aerodynamic design of low wave-drag supersonic biplane using inverse problem method
Ballistic range experiment on the low sonic boom characteristics of supersonic biplane
Design of supersonic biplane aircraft concerning sonic boom minimization
Supersonic biplane —— a review
Flow choking and its hysteresis problems, however, occured at their off-design conditions. It was shown that these off-design problems could also be resolved by utilizing slats and flaps. Finally, a study on the aerodynamic characteristics of wing-body configurations was conducted using the tapered biplane wing. In this study a body was chosen in order to generate strong shock waves at its nose region. Preliminary parametric studies on the interference effects between the body and the tapered biplane wing were performed by choosing several different wing locations on the body. From this study, it can be concluded that the aerodynamic characteristics of the tapered biplane wing are minimally affected by the disturbances generated from the body, and that the biplane wing shows promise for quiet commercial supersonic transport. (C) 2010 Elsevier Ltd.]]>
Adjoint-based aerodynamic optimization of supersonic biplane airfoils
This paper addresses the aerodynamic performance of Busemann-type supersonic biplanes at both design and off-design conditions. An adjoint-based optimization technique is used to optimize the aerodynamic shape of the biplane to reduce the wave drag at a series of Mach numbers ranging from 1.1 to 1.7, at both acceleration and deceleration conditions. The optimized biplane airfoils dramatically reduces the effects of the choked flow and flow-hysteresis phenomena, while maintaining a certain degree of favorable shockwave interaction effects at the design Mach number. Compared with a diamond-shaped single airfoil of the same total thickness, the wave drag of our optimized biplane is lower at almost all Mach numbers, and is significantly lower at the design Mach number.
Biplane wing twin body fuselage configuration for innovative supersonic transport
In this paper, a biplane-wing/twin-body-fuselage configuration is discussed for advanced supersonic transport. The supersonic-biplane-wing concept has been proposed by Kusunose et al. ("Supersonic Biplane-A Review," Progress in Aerospace Sciences, Vol. 47, No. 1, 2011, pp. 53-87), and a remarkable drag reduction in supersonic flow conditions has been demonstrated in the literatures. Motivated by the wave reduction effect of the supersonic biplane airfoils, a twin-body-fuselage concept has also been proposed by the present authors. Wave-drag reduction was achieved by an optimal twin-body-fuselage configuration. In this research, therefore, the biplane-wing concept and the twin-body-fuselage concept are merged to propose an innovative supersonic transport configuration. The wave-drag characteristics, as well as the wave-drag reduction, are illustrated by inviscid computational fluid dynamics computations at the design Mach number of 1.7. The inviscid (wave) drag of the proposed configuration is much smaller than that of the Sears-Haack single body with a tapered wing of a diamond-wedge airfoil. The increment of the skin-friction drag is also discussed for the proposed configurations. Based on the total drag analysis, the superiority of the biplane-wing/twin-body-fuselage configuration over the conventional configurations is clearly demonstrated.
Low boom/low drag design optimization of innovative supersonic transport configuration
Parametric study of an axisymmetric busemann biplane configuration
基于Busemann双翼构型的超音速导弹减阻技术研究
Drag reduction method for supersonic missile based on Busemann biplane concept
布泽曼双翼及其壅塞问题研究
Research on Busemann biplane airfoil and its choked flow problem
超声速双层翼翼型的阻力特性研究
Numerical simulation of blowing control based on limited wingspan model
Busemann双翼流动壅塞及减阻数值模拟
Numerical simulation of Busemann biplane chocked flow and drag reduction
新型目标压力分布下的Licher双翼反设计方法研究
为了提高超声速气动构型的升阻比,减小激波阻力,使用反设计方法结合CFD技术优化Licher双翼,实际算例表明,来流马赫数1.7,无粘情况下只需迭代15步即可得到优化结果,优化后翼型波阻可减小25.5%,升阻比提高30.5%。随后依据翼型目标压力分布这一反设计关键点,分析了非零迎角下翼型各边的受力情况,指出了原目标压力分布的不足,并提出了一种新的阶梯形目标压力分布形式,该方法的优化结果可使升阻比提高49.8%。此外基于NS方程的优化结果表明,原目标压力分布的优化效果被削弱,升阻比仅能提高17%,而新目标压力分布的优化结果受到的影响较小,升阻比仍可提高49.2%,说明在考虑流动粘性特征时,阶梯形目标压力分布形式更具实用价值。
Inverse design method for the Licher biplane with a new target pressure distribution
An inverse design method has been applied for the Licher biplane with modern computational fluid dynamics (CFD) technique to increase the lift-drag ratio and reduce the shock wave drag during its the supersonic flight regime. An example of numerical simulation demonstrates that the wave drag can be reduced by 25.5% and the lift-drag ratio rises by 30.5% simultaneously using this optimization algorithm with inviscid flow assumption as the free stream Mach number is 1.7. In addition, it takes about 15 iterations to get convergent results, which demonstrates that the inverse design method in this paper is efficient. A new stair target pressure distribution, as the key of the inverse design method, has been developed to overcome setbacks of the original one by some analyses of aerodynamic forces. With the new target, the lift-drag ratio can increase up to 49.8%. Furthermore, the Euler equations in the optimization procedure have been replaced by the Navier-Stokes equations to investigate the influence of viscous fluid. The results indicate that the effect of the optimization with the original target pressure distribution is beyond neglect, the lift-drag ratio increases only by 17.0%. However, the results of the new stair target pressure distribution, with more potential practical value, stay almost the same level.
高超声速可变形双翼气动特性
Aerodynamic characteristics of hypersonic morphing biplane
基于Busemann双翼的三维高超声速机翼研究
Research on three dimensional hypersonic wing based on Busemann biplane
Design development strategies and technology integration for supersonic aircraft of low perceived sonic boom
