Effects of radius ratio on turbulent concentric annular pipe flow and structures

The effects of radius ratio on fully-developed turbulent concentric annular pipe flow and structures are investigated using direct numerical simulations (DNS). In order to study the radius ratio effects on the flow, four radius ratios of a concentric annular pipe (for Ri∕Ro=0.1–0.7) are compared at a fixed Reynolds number. Here, Ri and Ro are the radii of the inner and outer pipes, respectively. It is observed that the radius ratio influences the interaction of two boundary layers developed over the inner and outer cylinder surfaces, and has a significant impact on the turbulent flow structures and dynamics. The characteristics of the flow field are investigated in both physical and spectral spaces, which include the analyses of the first- and second-order statistical moments, budget balance of the transport equation of Reynolds shear stress, two-point correlation coefficients, and premultiplied spectra of velocity and vorticity fluctuations.