出口宽高比对双涵道S弯喷管流动特性的影响

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

关键词:  双S弯喷管  流动特性  排气混合器  宽高比  气动性能

Key words:  Double serpentine nozzle  Flow characteristic  Exhaust mixer  Aspect ratio  Aerodynamic performance

摘要:

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。

Abstract:

In order to clarify the influence mechanism of aspect ratio on flow characteristic 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 nozzle under the conditions of different aspect ratios had been simulated numerically. Results are obtained as follows： The flow features around exhaust mixer were changed hardly on the conditions of different aspect ratios. The stretching of streamwise vortices was more serious at the transversal inflections meanwhile the vorticities decreased at the longitudinal inflections as aspect ratio increased constantly. The vorticities loss and mixing loss were enlarged in the former directly while it diminished in the later. The shear stress at the wall surface of two inflections and linear section regions decreased gradually with increment of aspect ratio， where the friction loss and local loss were weakened effectively. However， the curved extents of limiting streamlines on the upper and lower wall surface were strengthened apparently which expanded toward outside firstly and then contracted toward innerside along the flow direction. Correspondingly， the aforementioned friction loss in the serpentine nozzle were enlarged remarkably. The axial velocity of plume potential core near nozzle exit increased gradually as the aspect ratio rose while its axial length was shortened dramatically. As a result of coupling effects between exhaust mixer and different nozzle geometric configurations， there appeared the opposite variety trends of multiple flow losses. Generally， the aerodynamic performance of double serpentine nozzle was almost unchanged.