Manipulating desired internal turbulent flow characteristics inside a pipe through changing the shape of the cross section is a beneficial idea for flow control and turbulence management. However, the effect of applying altered cross sections on developing turbulent structures should be fully studied to understand the underlying physics of turbulent pipe flow with non-circular geometry. In the current numerical study, large eddy simulation of internal turbulent flow inside circular and non-circular pipes has been performed at low Reynolds numbers ranging from 5000 to 10 000. The circular pipe is flattened to make non-circular pipes having different aspect ratios of 2 and 4 to investigate the turbulent flow behavior in detail. The pipe flattening causes an increased number of coherent vortices and the development of secondary flow, which enhances turbulence intensity, especially in the near-wall region. Several parameters, including mean and fluctuating velocities, Reynolds normal and shear stresses, turbulent kinetic energy (TKE), and vorticity, are analyzed to compare flow characteristics in different Reynolds numbers, considering the influence of varying cross-sectional areas. Flattening the pipe significantly amplifies turbulence intensity and enhances the flow activity, resulting in strengthened total Reynolds stress, elevated TKE, and stronger vorticity. Furthermore, non-circular pipes have higher wall shear stress compared to the round pipe, and this raised value causes the formation of secondary flow inside flattened pipes, while the friction coefficient value remains almost constant at the same Reynolds number for all pipes.
Azarhazin et al. (2026) studied this question.