Investigating Reynolds number effects in turbulent concentric coaxial pipe flow using stochastic one‐dimensional turbulence modeling.

The present study numerically investigates turbulent momentum transfer in concentric coaxial (annular) pipe flow with small radius ratios (η=Ri/Ro=0.1,0.04,0.02)$(\eta ={R}_{i}/{R}_{o}=0.1,0.04,0.02)$. To model the flow, a stochastic one‐dimensional turbulence (ODT) model formulated for cylindrical geometry is used that provides full‐scale resolution along a representative radial coordinate. The present investigation extends the model validation by Tsai et al. (PAMM, 22:e202200272, 2023), to radius ratios smaller than 0.1 and addresses boundary layers with strong spanwise curvature effects. The focus is on the assessment and analysis of statistical flow features in the vicinity of the inner cylinder wall, particularly in cases with small radius ratios. Following Boersma & Breugem (Flow Turbul. Combust., 86:113–127, 2011), classical boundary‐layer and mixing‐length theory is utilized to analyze the model predictions. The results demonstrate that the ODT model captures leading‐order curvature and mixing‐length effects by its physics‐compatible construction. Utilizing the model for extrapolation to high Reynolds numbers inaccessible to conventional high‐fidelity numerical approaches shows that curvature effects persist and nonlocally affect the entire boundary layer. The model results provide support for a spanwise‐curvature‐modified wall function. [ABSTRACT FROM AUTHOR]