Purpose

Control over large-scale coherent structures and stream-wise vortices lead to enhanced entrainment/conservation of the jet which is desirable for most free jet applications such as design of combustion chamber in jet engines and flame length elongation of welding torch used for metal cutting.

Design/methodology/approach

A co-flow nozzle with lip thickness of 2 mm, between the primary (inner) and secondary (outer) flow, is selected. Three nozzle combinations are used, i.e. C–C (circle–circle), C–E (circle–ellipse) and C–S (circle–square) for acquiring comparative data. For these nozzle combinations, inner nozzle exit plane is kept as a circle, whereas the outer nozzle exit planes are varied to circle, ellipse and square. The exit plane area of outer nozzle for the nozzle combinations has equivalent diameter, D_e. The nozzles are fabricated in a way that the outer nozzle can be rotated along the longitudinal axis, keeping the inner nozzle intact.

Findings

The C–C nozzle combination is effective in low Mach number regime in decaying the jet, when the rotational component is introduced. Around 30% reduction in the jet core length is observed for the C–C nozzle combinations without any lip. The C–E nozzle shows sedative result in decaying or preserving the jet. The C–S nozzle combination shows interesting phenomenon, whereby the low subsonic case tends to conserve the jet by 15% and the higher subsonic case tends to decay the jet by 10%.

Originality/value

The developed nozzle systems show both conservative and destructive effect on the jet, which is desirable for the mentioned applications.

中文翻译：

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具有水平唇缘和形状过渡的旋转并流喷嘴

目的

对大规模相干结构和流向涡流的控制导致射流的增强夹带/守恒，这对于大多数自由射流应用而言是理想的，例如喷气发动机中的燃烧室设计和用于金属切割的焊炬的火焰长度伸长。

设计/方法/方法

选择了唇缘厚度为 2 mm 的并流喷嘴，介于主（内）流和辅（外）流之间。使用三种喷嘴组合，即C-C（圆-圆）、C-E（圆-椭圆）和C-S（圆-正方形）来获取比较数据。对于这些喷嘴组合，内喷嘴出口平面保持为圆形，而外喷嘴出口平面则变化为圆形、椭圆形和方形。喷嘴组合的外喷嘴的出口平面面积具有等效直径_De。喷嘴的制造方式使外喷嘴可以沿纵向轴线旋转，从而保持内喷嘴完好无损。

发现

当引入旋转分量时，C-C 喷嘴组合在低马赫数状态下衰减射流是有效的。对于没有任何唇缘的 C-C 喷嘴组合，观察到喷射核心长度减少了约 30%。C-E 喷嘴在衰减或保留射流方面显示出镇静效果。C-S 喷嘴组合显示出有趣的现象，即低亚音速情况倾向于将射流保存 15%，而更高的亚音速情况往往会使射流衰减 10%。

原创性/价值

开发的喷嘴系统对射流显示出保守和破坏性影响，这对于上述应用是可取的。