Numerical Study of Incompressible Flow Through a Pipe with an Orifice Constriction Using Ansys Fluent

Abstract

Incompressible flows with sudden contractions, such as those created by orifice plates, exhibit complex behaviour including flow acceleration, pressure losses, and downstream separation. Predicting these features accurately remains challenging due to the sensitivity of CFD results to mesh resolution, flow regime, and turbulence modelling. This study investigates how mesh quality, Reynolds number variation, and turbulence model selection influence pressure and velocity predictions in a pipe containing an orifice contraction. Results indicate that mesh refinement improves accuracy, with minimal benefit beyond the medium mesh. Increasing the Reynolds number substantially alters flow behaviour, with the inlet pressure rising by approximately 9.5% from laminar to transitional conditions, while the pressure difference in the turbulent regime becomes about 52% lower than in the transitional regime. Among the turbulence models tested, the Realizable k-ε and k-ω SST models show better agreement with expected separation patterns compared to the Standard k-ε. Overall, the findings highlight the importance of mesh selection, flow regime characterisation, and turbulence modelling in achieving reliable CFD predictions for orifice-induced pipe flow.