Atomization, Transport, and Numerical Wall-Trapping Characteristics of Drag-Reducing Agent Droplets in Hydrogen-Blended Natural Gas Pipeline Inlet Sections

Research on atomized drag-reducing agent (DRA) delivery in hydrogen-blended natural gas (HBNG) pipelines is limited, although inlet-section droplet transport and wall interaction are of practical importance. A three-dimensional CFD–DPM model of a 15m straight pipe equipped with a pressure–swirl hollow-cone atomizer was developed to evaluate the effects of atomization pressure drop, injection mass flow rate, spray cone angle, nozzle orifice diameter, hydrogen blending ratio, and operating pressure. Numerical robustness was assessed through mesh and parcel-number independence tests, turbulence-model sensitivity analysis, representative simulations at MPa-level operating pressures, and qualitative comparison with published pressure–swirl spray experiments. Increasing atomization pressure drop from 0.5 to 5MPa reduced the Sauter mean diameter from 120.07 to 32.85μm and the numerical wall-trapping ratio from 32.96% to 13.68%, with diminishing changes above approximately 2MPa. Higher injection mass flow rates increased droplet size and numerical wall trapping, whereas larger cone angles intensified radial migration and caused severe inlet-localized trapping at 80∘. Nozzle orifice diameter and hydrogen blending ratio showed weaker effects. Increasing operating pressure from 101,325Pa to 2MPa reduced the SMD from 54.60 to 9.91μm and the numerical wall-trapping ratio from 15.88% to 5.96%. These model-dependent trends require high-pressure spray, flow-loop, or field validation before engineering application.