【作者】 雷志军；

【导师】 朱俊强； Ali Mahallati；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2011， 博士

【摘要】 波瓣混合器在中小涵道比涡扇发动机中有着广泛的应用前景,其对于提高尾气掺混效率、增加输出推力、降低耗油率、减少排气噪音和抑制红外辐射等都具有十分重要的意义。长期以来,学者们一直致力于研究轴向均匀进气条件下波瓣射流的掺混机理及其几何参数的优化设计,但对上游尾迹及进口预旋作用下波瓣射流的掺混过程及作用机理,研究成果甚少见诸报道。本文以某真实发动机波瓣混合器为研究对象,以能提供不同上游尾迹和进口气流切向气流角度的低速同心双环流风洞实验台(隶属于加拿大国家研究理事会燃气透平实验室,GTL-NRC)为载体,以七孔探针、热线及表面油流显示技术为测试手段,并辅之以数值计算,在深入理解波瓣射流掺混机理的基础上,探讨了进口有无预旋条件下波瓣射流掺混过程的具体变化,重点分析了上游尾迹和进口预旋影响射流涡系结构形成、发展及相互作用直到破碎的全过程,并详细评估了进口预旋对射流掺混气动性能的影响。在对常规波瓣研究工作的基础上,通过对波瓣切凹扇形处理,探讨了凹扇形缺口对波瓣射流掺混机理的影响机制,并分析了上游尾迹、进口预旋及掺混长度对切凹扇形波瓣射流掺混过程及气动性能的影响。对波瓣射流掺混机理的研究表明,波瓣特殊的几何外形诱导形成了大尺度流向涡,流向涡与正交涡的相互作用及自身破碎过程产生大量的小尺度湍流斑,这对加速波瓣射流掺混过程起着决定性的作用,导致大部分波瓣射流掺混过程能在波瓣下游2倍等效水力直径的范围内完成。在进口预旋作用下,流向涡及正交涡强度都有所增强,它们之间的相互作用依然支配着波瓣射流的掺混过程。波谷附近的外涵刺入气流一方面拉伸、扭曲正交涡,一方面在强进口预旋工况下与内涵气流形成逆时针旋转的附加流向涡,进一步改善了常规波瓣混合器的射流掺混过程。中心锥与波谷之间的有旋泄漏流动卷吸了大量的高能内涵气流,并借助径向扩散挤压外围流体的方式强化了外围涡系之间的相互作用,有利于加速波瓣射流的掺混过程。随着进口预旋的增强,有旋泄漏流加速射流掺混的作用变得越来越重要。但在较大的进口预旋条件下,波瓣吸力面出现的流动分离及中心锥下游形成的大范围环形回流区,将导致射流总压损失的增加及发动机输出推力的大幅下降。在切凹扇形波瓣射流中,流向涡从凹扇形缺口顶点开始被逐步引入,由此引起的射流预掺混过程抑制了正交涡的发展。正交涡在凹扇形缺口下游的不同扩散速度造成其自身的拉伸及扭曲,进而诱导形成了小尺度附加流向涡,该附加流向涡与大尺度流向涡的相互作用,虽然不一定增强流向涡强度,但有利于加速波瓣射流的掺混过程。在较强的进口预旋作用下,沿径向向内的外涵刺入气流与径向向外的内涵气流相互作用是附加流向涡形成的主要原因。切凹扇形处理虽然不影响中心锥附近的有旋泄漏流及其下游回流区,但降低了波瓣的抗预旋能力,导致波瓣吸力面较大范围的流动分离。当进口切向气流角小于20。时,进口预旋有利于加速波瓣混合器的射流掺混,且不会导致过高的总压和推力损失。在弱进口预旋条件下,切凹扇形处理有利于波瓣总体性能的提升；在强进口预旋条件下,给予波瓣一定的进口几何角或者对波谷进行斜切处理,将有利于提高波瓣适应强进口预旋的能力。更多还原

【Abstract】 The lobed mixer is entensive used in the low and intermediate bypass ratio turbofan engines, resulting in enhancement in jet mixing efficiency, increase in net thrust, a reduction in fuel consumption, decrease in jet noise and, in some cases,reduced infrared signature. Since 1960s, considerable researches have been carried out on the jet mixing mechanism of the lobed mixer and geometry optimization at the design point of the turbofan engine, which means the inlet condition is uniform flow with the axial direction. While, at the off-design points, i.e. take-off, landing or with high inlet swirling flow due to the usage of high loading turbine blade, it is rarely to find the relative paper which studies the effect of inlet swirl on the mixing and performance of the lobed mixer. Therefore, this paper works on the lobed mixer of a real turbofan engine on a co-annular, low speed, open circuit wind tunnel at the Gas Turbine Laboratory of the National Research Council of Canada. The seven-hole probe, hot-wire and surface oil-flow visualization was used to measure the flow field at inlet planes, downstream of the lobed mixer or lobe’s surface, and the simulation was also carried out to offer the detailed information of the jet mixing flow as an assistant of the measurement.In this paper, the jet mixing mechanism of the loed mixer is studied with the uniform inlet flow without swirl, firstly. And then, the swirl vanes were used to generate the inlet swirling flow with different swirl angle to stuty the effect of inlet swirl on the formation, development, interaction and break-down of the vortical system downstream of the lobed mixer, the aerodynamic performance of the lobed jet flow is estimated under the inlet swirl condition. Further more, this paper also studied the mixing mechanism of the scalloped lobed mixer with/without inlet swirl, and the effect of swirl vanes’wakes and the length of the mixing tube on the performance of the scalloped lobed mixer is discussed in this paper too.Based on the analysis on the jet mixing mechanism of the lobed mixer, the special 3D contour of lobed mixer induces the large scale streamwise vortices, with the length sacle of height of the lobe. With the diffusion of the jet flow, the interaction between streamwise vortices and normal vortices and their break-down generates lots of turbulent eddies, which dominate the jet mixing of the lobed mixer. Most of the jet mixing happens in the range of two equivalent hydraulic diameter downstream of the lobed mixer. Under the highly inlet swirl conditions, the interaction between the streamwise vortices and normal vortices, which are enhanced by the inlet swirl, still dominates the lobed mixing flow. The penetration flow around the lobe’s trough stretches and deforms the normal vortices, even generates counter-clockwise rotating additional streamwise vortices by interaction with the core flow, and improves the jet mixing of un-scalloped lobed mixer. The leakage swirling flow between the centre-body and lobe’s trough entrains considerable core fluids with high momentum, and enhances the self-interaction of outer vortical system by extruding the outer fluid. All of thses phenomena enhance the lobed jet mixing, and the effect of the leakage flow becomes more important with the increasing inlet swirl. However, under highly inlet swirl conditions, the separation bubble presenting on the the suction surface of the lobe and the large-scale recirculation zone appearing downstream of the centre-body due to the high swirling leakage flow causes increasing total pressure loss and thrust loss.The streamwise vortices is introduced gradually from the tip point of the scalloping curve, and the induced flow mixing bates the strength of the normal vortices. The normal vortices are stretched and deformed by the scalloped notch due to their own different diffusion rate downstream of the trailing edge of scalloped lobed mixer, and induced the formation of the small-scale additional streamwise vortices. The interaction between the addition streamwise vortices and the large-scale streamwise vortices may not increase the streamwise vorticity, but it really enhance the jet mixing due to the generation of considerable turbulent eddies during their interaction. Under highly inlet swirl conditon, the additonal streamwise voritces near the lobe’s trough induced by the interaciton between the penetration flow and the core flow due to their opposite radial velocity. The leakage flow around the centre-body is not sensitive to the scalloping notch of the scalloped lobed mixer. On ther other hand, the scalloping notch decrease the resistance of scalloped lobed mixer to the inlet swirl, resulting in the larger separation bubble on the suction surface of the lobe.Anyway, when the inlet swirl angle is less than 20°, the inlet swirl enhances the jet mixing of lobed mixer, and the penelty of total pressure loss or thrust loss is acceptable. For the low inlet swirl, the scalloping cut can increase the aerodynamic performance of the lobed mixer; for the high inlet swirl, the lobe with a certain degree of metal angle or scarfing the lobe’s trough may increase the resistance of lobe mixer to the high inlet swirl.更多还原