Numerical and experimental investigation of roughness and temperature effects on mean velocity profiles in pipe flow

Abstract The mean velocity profile is essential for characterizing near-wall dynamics in turbulent pipe flow and is widely used in engineering applications involving momentum and heat transfer. This study investigates the effects of surface roughness and temperature on the mean velocity profile. Extensive experiments were conducted at the Izmir Katip Celebi University Civil Engineering Flow Loop using water over a range of flow rates, relative roughness values, and temperatures. A numerical model was developed in OpenFOAM using the PIMPLE algorithm, which combines the Pressure Implicit with Splitting of Operators (PISO) and the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE). The simulations were performed using the RNG κ-ɛ turbulence model. The numerical predictions showed good agreement with the experimental results, with an absolute average percentage error (AAPE) of 10.38% for the tested conditions. For smooth pipes, the velocity profile closely matched the classical u + = y + relation in the viscous sublayer and the logarithmic law in the inertial sublayer. For y + > 30, the power-law velocity distribution also fits well, supporting its suitability for modeling fully turbulent regimes. Increased roughness height significantly disrupted the logarithmic region, leading to pronounced deviations in the mean velocity profile. Although both smooth and rough pipes demonstrated similar trends with temperature variation, the roughness Reynolds number had a stronger influence on these deviations. Elevated temperatures caused a noticeable downward shift in the mean velocity profile, particularly in the near-wall region, which was consistent with viscosity-driven changes in wall scaling. Overall, the validated numerical model provides a useful tool for predicting turbulent flow behavior under the investigated conditions.