Abstract Wall-resolved large eddy simulations (LES) are performed to investigate turbulent heat transfer in a rough pipe over a range of Prandtl (Pr) numbers. The rough surface is generated using a controlled numerical procedure that allows independent specification of roughness correlation length, amplitude, and skewness; a statistically Gaussian height distribution is considered as a baseline case. The resulting geometry is used directly in an LES framework implemented in OpenFOAM. Simulations are conducted at a bulk Reynolds number (Re) of 11,700 for Pr = 0.5, 1, 2, and 5, and are extended to additional Re= (2000−15,000) to assess the robustness of global trends. Time-averaged velocity and temperature profiles, turbulent heat fluxes, and Reynolds stresses are analyzed to examine the interaction between roughness-induced mixing and Pr number-dependent thermal diffusion. Relative to a smooth pipe, the rough surface produces a systematic downward shift of the mean temperature profile, indicating enhanced heat transfer across all Pr numbers. The wall-normal turbulent heat flux closely follows the Reynolds shear stress, demonstrating a strong dynamical coupling between scalar and momentum transport within the roughness layer. Probability density functions of the local Nusselt number reveal pronounced spatial variability linked to surface geometry. A sheltering analysis based solely on surface visibility to the incoming flow distinguishes weakly ventilated regions with suppressed heat transfer from exposed windward faces that host intense thermal events. A complementary zonal analysis based on roughness height shows that local heat-transfer enhancement becomes increasingly sensitive to surface elevation as the Pr number increases. For the Gaussian-type roughness considered here, however, the overall influence of Pr number on global and local heat-transfer statistics remains comparatively modest, suggesting a dominant role of geometric sheltering effects. Re number sweeps of global metrics further demonstrate that roughness-induced heat-transfer enhancement and thermal performance increase monotonically with Re number, confirming that the identified mechanisms persist across a broader range of operating conditions.
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