Effects of swirling secondary flow on the decay characteristics of non-circular under-expanded supersonic primary jets were experimentally studied. Primary jet is issuing from a convergent-divergent nozzle with different exit geometry such as circle, cruciform, triangle and rectangle. In this study, two different methods were used to impart swirl on the secondary flow as follows, (i) introduction of- angular vanes inside the secondary flow duct and (ii) using tangential inlets at the secondary flow duct. This swirling secondary flow influences the boundary condition of the primary jet and results in reduction of jet core length and shock train length, it also enhances the jet decay rate. Maximum shock train length reduction of 70 % is achieved when swirling secondary flow (tangential injection method) is introduced over the circular primary jet.

中文翻译：

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旋流二次流对超扩径非圆形超音速射流的影响

实验研究了回旋二次流对非圆形超膨胀超音速一次射流衰减特性的影响。初级射流从具有不同出口几何形状（例如圆形，十字形，三角形和矩形）的会聚发散喷嘴发出。在这项研究中，采用了两种不同的方法在次级流上产生涡流，如下所示：（i）在次级流管内引入角形叶片，以及（ii）在次级流管处使用切向入口。这种涡旋的次级流影响初级射流的边界条件，并导致射流芯长度和冲击波列长度的减小，这也提高了射流的衰减率。当在圆形初级射流上引入旋流二次流（切向注入法）时，最大冲击波列长度减少了70％。