The physical properties of bird feathers during flight constitute one of the significant concerns in the field of biomimetic mechanics. In this paper, the CFD/CSD numerical simulation method is adopted to calculate and analyze the deformation as well as mechanical characteristics of feather microstructure in the airflow, revealing the physical mechanism by which feathers exhibit thick and fluffy at rest, but keep close to the bird’s skin surface to maintain the surface smoothness during flight. Initially, by observing the bird feathers with optical microscope, the feather structure is decomposed into typical simple microstructures to imitate the barb element, thus modeling the shape and structure of the feather. Then, the deformation and mechanical characteristics of two typical modeling structures (flaky barb element and branch barb element) are analyzed and compared by CFD/CSD method. Finally, based on the aforementioned flaky barb element model, further research is conducted on the influence mechanism of the incoming flow direction on the deformation feature of barb element, as well as the deformation and mechanical characteristics of multiple arranged barbs. The results show that within a certain range of inflow direction, the feather maintains the deformation tendency of keeping close to the bird’s skin surface in the airflow. This tendency will change only when the airflow is almost perpendicular to the feather rachis. When the sideslip angle of inflow is
45^\circ 
, the downward deformation of barb element along the skin surface normal is the most significant, with a tip displacement of approximately 97% of its initial height. The multi-row arranged barb elements experienced a gradual decrease in aerodynamic load in the flow direction, with a maximum difference of about 11% compared to the leading barb element against the wind. This research has a clear academic value for understanding the mechanical properties of bird feathers when flying.
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