The Development of Swirling Decaying Laminar Flow in an Annular Pipe

Work on the hydrodynamic entry length of pipe and duct flow has been well studied over the years. The assumption of fully developed flows is commonly used in many practical engineering applications (e.g. Moody's chart). For laminar axial pipe flow, the hydrodynamic entry length can be found through the monomial proposed by Kays, Shah and Bhatti (KSB) (Lh=0.056ReDh). In contrast, several approximations exist for fully turbulent flows (i.e. 10Dh-150Dh). Through theoretical and numerical investigations, the hydrodynamic entry length for swirling decaying pipe flow in the laminar regime is investigated. It was found that, the development length Lh for the axial velocity profile changes when a tangential component is added to the mean flow. The reduction in the hydrodynamic length was found to be dependent on the inlet swirl angle.. The results indicate that a modification can be made on the KSB equation for two-dimensional swirling annular pipe flow.