Serpentine nozzles possess excellent advantages in improving the stealth ability of aero-engine exhaust. For a real turbofan, the flow characteristics of the serpentine nozzle are evidently affected by the geometric parameters and the complex exhaust mixer. This is an issue that needs to be seriously considered. The aim of this paper is to investigate the influences of the critical geometric parameters on the serpentine nozzles for turbofan. The detailed flow field of the serpentine nozzle for a small-scale model is precisely measured. The influence of the ratio of axial length to inlet diameter on the flow field and on the aerodynamic performance of the serpentine nozzle is numerically explored. Results show that the pressure on the upper wall first drops rapidly and then ascends with the local minimum occurring at the first inflection. The relative error between the numerical prediction and the experimental data is less than 2%. The calculated distributions of the expansion-shock waves and the jet shear layers are highly consistent with the schlieren flow visualization data. Thus, the reliability of the numerical method is effectively confirmed. The internal flow and the external jet features of the serpentine nozzle are extremely non-uniform. Such poor uniformity is reflected in the phenomena including the existence of the local high-shear-stress regions and the high-velocity regions, the multiple bending of the limiting streamlines, as well as the velocity fluctuation of plume core. The aerodynamic performance of the serpentine nozzle first enhances greatly and then stays unchanged as the value of $L/D$ rises. The vortex loss and the shock loss both reduce evidently owing to the flow separation and the disappearance of the shock wave during the rise of $L/D$ from 2.2 to 2.4. The value of the discharge coefficient and the thrust coefficient increases by 1.5% and 2.1%, respectively. The length of the plume core is effectively shortened due to the disappearance of the shock wave inside the nozzle.

蛇形喷管在提高航空发动机排气隐身能力方面具有优异的优势。对于真正的涡扇发动机，蛇形喷嘴的流动特性明显受到几何参数和复杂排气混合器的影响。这是一个需要认真考虑的问题。本文的目的是研究关键几何参数对涡扇蛇形喷管的影响。精确测量了小型模型蛇形喷嘴的详细流场。数值研究了轴向长度与入口直径之比对流场和蛇形喷嘴气动性能的影响。结果表明，上壁压力先快速下降然后上升，局部最小值出现在第一个拐点处。数值预测与实验数据的相对误差小于2%。膨胀冲击波和射流剪切层的计算分布与纹影流可视化数据高度一致。从而有效地证实了数值方法的可靠性。蛇形喷嘴的内部流动和外部射流特征极不均匀。这种均匀性差体现在局部高剪应力区和高速区的存在，极限流线的多次弯曲，以及羽核速度波动等现象。蛇形喷管的气动性能先大幅度提高后保持不变，为$\mathrm{大号}/丁$上升。涡流损失和激波损失均由于上升过程中的流动分离和激波消失而明显减小$\mathrm{大号}/丁$从 2.2 到 2.4。流量系数和推力系数的值分别增加了1.5%和2.1%。由于喷管内冲击波的消失，羽核长度有效缩短。