This paper focuses on the internal flow development of an S-shaped diffusing duct. Based on the experimental result of total pressure recovery coefficient, the Reynolds stress model (RSM) was selected as a suitable turbulence model for the present study. The numerical results show that 6.2 times the area ratio of the exit to inlet and the aggressive deflection at the first bend of the lower wall lead to strong adverse pressure gradient and very large flow separation, and create a pair of counter-rotating vortices along streamwise direction. The duct diffuser efficiency is 72.37 %. The area-averaged total pressure recovery coefficient at the exit of the duct is 0.9814, and the synthesis distortion index DC (60) is 0.7081.

中文翻译：

---

通过S形扩散管进行流量开发

本文着重于S形扩散管的内部流动发展。根据总压力恢复系数的实验结果，选择雷诺应力模型（RSM）作为适合本研究的湍流模型。数值结果表明，出口与入口的面积比为6.2倍，并且在下壁的第一弯处出现剧烈的挠曲，会导致强烈的逆压梯度和非常大的分流，并沿流向产生一对反向旋转的涡流方向。管道扩散器的效率为72.37％。导管出口的面积平均总压力恢复系数为0.9814，合成变形指数DC（60）为0.7081。