Characteristics and mechanism of turbulent drag reduction in microgrooves in natural gas transportation pipelines.

The article focuses on the numerical simulation and analysis of drag reduction effects of semi-circular and alternating wide-narrow microgroove structures on large-diameter natural gas pipelines under high Reynolds number turbulent flow conditions. Using large eddy simulation (LES) of methane gas flow in a 426 mm diameter pipe, the study finds that these microgroove structures can reduce drag by up to approximately 18% at optimal dimensionless groove widths (s+) between 16.96 and 20.84, corresponding to Reynolds numbers around 2.6 × 10^5. The drag reduction mechanism involves suppression of vortex rising and spreading motions near the wall, increased viscous sublayer thickness, and displacement of highly disturbed turbulent regions away from the groove surface, thereby weakening near-wall turbulence and pulsation velocities. At higher Reynolds numbers or larger groove spacings, vortex intrusion into grooves increases, leading to drag increase. This research addresses a gap in understanding drag reduction in large-diameter natural gas pipelines and highlights the potential of bionic non-smooth surface microgrooves for energy-efficient pipeline transport.