The microscale gas–particle interaction is the determining process for the macroscopic flow behaviors of gas–particle systems. Anisotropic Stefan flow is often manifested at the surface of the biomass particle when thermally decomposed. However, the influence of the anisotropic Stefan flow on the gas–particle interactions is not well understood. To this end, particle-resolved direct numerical simulations were carried out in this research to explore the momentum interactions between the gas flow and a static particle emitting mass flux at its surface. A signed distance function based immersed boundary method is first extended to account for the Stefan flow at the gas–particle interface and successfully validated by comparing with literature results in the case of no Stefan flow or uniform Stefan flow. It is found that the presence of the outward uniform Stefan flow leads to an expanded wake formation and the intensity of the vortex (Re ≥ 40) is enhanced as result of the Stefan flow. Subject to the impact of anisotropic Stefan flow parallel to the main flow, the low-speed region in the front and rear of the particle is reduced when the Stefan flow goes inwards, resulting in the increase in the drag coefficient. As the Stefan flow is outward, the low-speed region in the front of the particle is pushed forward by the emitting gas and the velocity magnitude in the wake region is increased, which behaves like an enlargement of the gas cushion and leads to a significant reduction of the drag coefficient comparing with a uniform Stefan flow. In contrast, the impact of anisotropic Stefan flow with the direction perpendicular to the main flow on the fluid–particle drag interaction is less significant due to the fact that the flow structure in the front and rear regions is not significantly disturbed.
