CFD Analysis of Transition & Turbulent Flow Through Pipes

Accurate prediction of the pipe pressure loss is important for engineering applications. But the Reynolds number does not definitively determine whether the flow is laminar or turbulent. Therefore, relying solely on Reynolds number to select the specific equation can be inaccurate, as the actual flow regime might differ from prediction. In this study, computational fluid dynamics (CFD) simulations were conducted using the ANSYS fluent 2023 R2 with the standard k–ε turbulence model and standard wall functions to analyze fully developed pipe flow across Reynolds numbers from 2,000 to 200,000, with varying wall roughness values. A mesh-independence study verified convergence beyond approximately 0.7x106 cells. The investigation systematically varied the inlet velocity and the surface roughness to quantify their effects on pressure loss; this simulated result was compared against theoretical predictions using the Darcy–Weisbach and Colebrook–White equations for transitional and turbulent flow. The findings revealed that CFD consistently predicted below 20% pressure losses in turbulent flow than theoretical models, particularly in the transitional regime where more than 200% difference was observed, highlighting limitations of conventional methods. Pressure loss was found to increase significantly with the inlet velocity, while the surface roughness exhibits comparatively minor influence. These results emphasize the importance of velocity control that minimizes energy loss in piping systems and demonstrate the capability of CFD to provide deep insight into pipe flow.