出口宽高比对双涵道S弯喷管流动特性的影响

为了明晰出口宽高比对基于真实排气混合器构型的S弯喷管流动特性的影响机制，数值模拟了不同出口宽高比下的双S弯喷管内/外流特性。结果表明：出口宽高比对排气混合器附近的流场特征影响较小，但增加出口宽高比导致喷管下游纵向转弯处的涡量减小，而涡的横向运动更加剧烈，由此带来的涡损失及内/外涵掺混损失沿纵向有所减小，沿横向持续增大。随着出口宽高比的增加，纵向两弯处及等直段区域的壁面剪切应力减小，相应的摩擦损失和局部损失降低；而上、下壁面极限流线的扩张-汇聚程度增强使得该区域的摩擦损失增大。宽高比的增加导致喷管出口附近气流的轴向速度逐渐增大，出口下游的尾喷流速度核心区长度逐渐缩短。不同出口宽高比条件下，喷管几何构型与排气混合器相互作用产生的多种流动损失的变化趋势相反，综合起来对S弯喷管的气动性能影响较小。

Effects of Aspect Ratio on Flow Characteristic of Serpentine Nozzle for Turbofan

In order to clarify the influence mechanism of aspect ratio on flow feature and aerodynamic performance of serpentine nozzle on the basis of real exhaust mixer configuration in the turbofan engine, the internal flow and external jet characteristic of double serpentine convergent nozzle under the conditions of different aspect ratios had been simulated numerically. Results are obtained as follow: The large flow separation regions are formed around the lobed mixer and tail cone, by which the streamwise vortexs are induced in the S-shaped circular-rectangular passage. The asymmetric distributions of x-streamwise vorticities are presented along the longitudinal direction, and it spreads out continuously along the flow direction. The flow features around exhaust mixer are changed hardly on the conditions of different aspect ratios. The stretching of streamwise vortices is more serious at the transversal inflections meanwhile the vorticities decrease at the longitudinal inflections as aspect ratio increases constantly. The vorticities loss and mixing loss are enlarged in the former directly while it is diminished in the later. The shear stress at the wall surface of two inflections and linear section regions decreases gradually with increment of aspect ratio, where the friction loss and local loss are weakened effectively. However, the curved extents of limiting streamlines on the upper and lower wall surface are strengthened apparently which expands toward outside firstly and then contracts toward innerside along the flow direction. Correspondingly, the aforementioned friction loss in the serpentine nozzle are enlarged remarkably. The axial velocity of plume potential core near nozzle exit increases gradually as the aspect ratio rises while its axial length is shortened dramatically. As a result of coupling effects between exhaust mixer and different nozzle geometric configurations, there appears the opposite variety trends of multiple flow losses. Generally, the aerodynamic performance of double serpentine nozzle is almost unchanged.