LES and DES of strongly swirling turbulent flow through a suddenly expanding circular pipe

A detailed numerical study is undertaken to investigate the physical processes that are engendered in the strongly swirling turbulent flows through a suddenly expanding circular pipe. The delayed DES Spalart-Allmaras (DDES-SA), improved DDES-SA (IDDES-SA), a dynamic k-equation LES (oneEqLES), dynamic Smagorinsky LES (dynSmagLES) and implicit LES with van Leer discretization (vanLeerILES) are scrutinized in this study. A comprehensive mesh study is carried out, and the results are validated with experimental data. The results of different operating conditions from LES and DES are compared and described qualitatively and quantitatively. The features of the flows are distinguished mainly on the basis of different levels of the centrifugal force for different swirls. The numerical results capture the vortex breakdown with its characteristic helical core, the Taylor-Görtler vortices and the turbulence structures. Further features are addressed because of the excellent agreement between the numerical and experimental data. The hybrid behavior of DDES-SA and IDDES-SA is discussed. The results confirm that LES and DES are capable of capturing the turbulence intensity, the turbulence production and the anisotropy of the studied flow fields.