Local investigation of the dynamic and thermal fields to characterize the transition onset from steady to unsteady laminar flow in a complex geometry

Abstract

The present work investigated numerically the onset of the transition from steady to unsteady laminar flow regime in a three dimensional complex geometry. The behavior of the dynamic and thermal fields of the chaotic fluid flow has been analyzed for numerous Reynolds numbers ranging from 190 to 550. Several parameters were used during this study to verify the fluid pattern such as; velocity and temperature profiles, secondary flow, flow intensity, helicity and the Nusselt number. It is found that at Re = 400, the symmetry of the flow is destroyed in the second and the third geometric periods whereas it still remains present in the first period which indicates the first step towards the transition. While at Re = 445, the symmetry is still preserved in the first period of the geometry, but the velocity begins to be unsteady with periodic variation at a single frequency where a clear impression can be given on the transition from the steady laminar regime to the unsteady regime. Results illustrate that the flow goes through intermediate steps to reach the unsteady domain before exiting the laminar zone. Moreover, the flow in the geometry of interest is not of the same nature so it can be totally or partially unsteady where different stages can be cited as; stable and symmetric flow, stable asymmetric flow, unstable flow with one or more frequencies and finally erratic flow.