Direct numerical simulation of turbulent concentric annular pipe flow part 1: Flow field

A direct numerical simulation is performed for a turbulent concentric annular pipe flow at Re_Dh = 8900 for two radius ratios (R₁/R₂ = 0.1 and 0.5). Main emphasis is placed on the transverse curvature effect on near-wall turbulent structures. Near-wall turbulent structures close to the inner and outer walls are scrutinized by computing the lower-order and higher-order statistics. The Reynolds stress budgets are illustrated to confirm the results of the lower-order statistics. A quadrant analysis of the Reynolds shear stress is explored to develop a sufficiently complete picture of the contribution of flow events to turbulence production (consumption). Probability density functions of the inclination angles of the projected vorticity vectors are investigated to analyze the transverse curvature effects on the orientation of the vorticity field. The present numerical results show that the turbulent structures near the outer wall are more activated than those near the inner wall, which may be attributed to the different vortex regeneration processes between the inner and outer walls.