Investigation of entrance length in circular and noncircular conduits by computational fluid dynamics simulation

Abstract

This study estimated entrance length of circular and noncircular conduits, including circle, triangle, square and hexagon cross-sectional conduit, by using computational fluid dynamics (CFD). For simulation condition, the length of non-circular conduit was 10 m and the hydraulic diameter was 0.2 m. The laminar flow with Reynolds number of 500 and turbulent flow with Reynolds number of 50,000 were applied to investigate water flow in conduits. The governing equations were solved iteratively by using ANSYS FLUENT 14.0. For turbulent flow simulation, standard k-epsilon and RNG k-epsilon model were employed to simulate turbulence. The preliminary results were validated by comparison with theoretical data. At first, grid independency was evaluated to optimize the model. Norm* was employed to investigate the entrance length, which is related to velocity. The simulated results revealed that the entrance length for laminar flow was longer than turbulent flow.