Study on the Regulation of Air Inlet Ratio on the Characteristics of Swirl Flow Field and Particle Suspension in Bulk Grain Transportation

ABSTRACT To address pipeline wear and excessive energy consumption caused by particle settling in pneumatic conveying of bulk grains, a tangential auxiliary‐air swirl device is proposed. Wheat particles (equivalent diameter 4 mm) are selected as the conveying medium. Based on a transient CFD–DEM coupling approach, numerical simulations are performed for a computational domain with a total length of 6.5 m and a main‐pipe inner diameter of 0.1 m, under the conditions of constant total inlet air flow rate and zero relative pressure at the main‐pipe outlet. The effects of the auxiliary‐to‐main air flow ratio ( ϕ = Q ₛ/ Q ₘ) on the swirl flow field and particle conveying characteristics are systematically investigated. Five operating conditions with ϕ ranging from 1/3 to 3 are considered. The results indicate that increasing ϕ leads to a nonlinear enhancement of the peak tangential velocity (reaching 19.88 m/s at ϕ = 3, approximately 15 times higher than that at ϕ = 1/3), while accelerating its axial decay, with a maximum attenuation of 55.57%. The mean axial velocity remains stable at 40.05 ± 0.03 m/s, whereas its fluctuation amplitude increases with ϕ . The total pressure loss rises significantly with increasing ϕ ; at ϕ = 3, the inlet pressure increases by 27.15%, accompanied by a 46.15% increase in energy consumption. Particle dynamics analysis reveals that ϕ = 1 yields the highest proportion of suspended particles and the minimum wall friction, representing the optimal operating condition. When ϕ < 1, particle deposition occurs at the pipe bottom, whereas ϕ > 1 induces annular near‐wall particle accumulation, thereby increasing the risk of pipe wear. This study elucidates the quantitative mechanisms by which auxiliary‐air parameters regulate swirl intensity and energy consumption, providing a theoretical basis for the optimization of swirl‐assisted grain pneumatic conveying systems.