3D numerical analysis of the unsteady turbulent swirling flow in a conical diffuser using Fluent and OpenFOAM

The paper presents three-dimensional numerical investigations of the unsteady swirling flow in a conical diffuser with a precessing vortex rope. The helical vortex breakdown, also known as precessing vortex rope in the engineering literature, benefits from a large body of literature aimed either at elucidating the physics of the phenomenon and building mathematical models, or at developing and testing practical solutions to control the causes and/or the effects. In this paper we investigate the unsteady hydrodynamic fields with a well-known precessing vortex rope computed with the FLUENT and OpenFOAM CFD codes. The main goal is to elucidate the physics of the phenomenon. The three-dimensional computational domain corresponds to the test section of a test rig designed and developed at Politehnica University of Timisoara. The same domain and grid with two millions cells is considered in both codes. The boundary conditions and problem setup are presented for each case. The unsteady pressure fluctuations along to the element of the conical diffuser are recorded. The numerical pressure fluctuations are validated against experimental data measured on the wall of the test rig. Consequently, the fundamental frequency and higher harmonics of the vortex rope is determined by a Fourier analysis