CFD-DEM study of powdered fuel jet flow characteristics with varied nozzle structure in stable stage

This study employs a coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) model to investigate the gas-particle two-phase jet characteristics under different nozzle convergence angles, throat lengths, and projection shapes. The results show that the convergence angle significantly affects the two-phase flow both inside and outside the nozzle. As the convergence angle increases, the peak position of the gas-phase velocity distribution shifts towards the nozzle inlet. Meanwhile, the peak drag force and particle expansion angle both increase. Increasing the nozzle throat length leads to deeper axial penetration of the high-speed gas-phase core, while reducing the peak velocity and moving it towards the nozzle inlet. A longer throat also increases the downstream particle velocity, decreases the peak drag force, and enlarges the particle expansion angle. For different nozzle shapes, the gas-phase velocity distributions in the square and circular nozzles exhibit similar overall trends, although slight differences in peak velocity are observed. The minimum gas velocity is 135.4 m/s in the circular nozzle and 148.3 m/s in the square nozzle. In addition to the central low-speed region, an extra low-speed zone appears along the diagonal direction in the throat of the square nozzle. Although the collision frequency is higher in the circular nozzle, the particle expansion angle in the square nozzle is slightly larger. These results clarify the role of nozzle geometry in regulating gas-particle two-phase jet development and provide a comparative basis for future powder-fuel nozzle optimization.