Abstract: The flow characteristics around 18 different flat plates with varying degrees of surface roughness were studied at a Reynolds number (The Reynolds number (Re) is defined as "Re=ρ" "U" _"0" "D/?" , where "ρ" represents the fluid density, "U" _"0" denotes the approach velocity of the fluid, D is the characteristic dimension of the flat plate, and "?" signifies the dynamic viscosity of the fluid) of 26,400 using numerical simulation methods. The study analyzed how the average drag coefficient("C" _"D,mean" ), fluctuating lift coefficient("C" _"L,rms" ), and Strouhal number (St) of both convex and concave plates varied with the degree of convexity and concavity. Additionally, the aerodynamic mechanisms behind these variations were examined from the perspectives of wall pressure and flow field. The results show that altering the longitudinal edges of a rectangular plate with either convex or concave modifications can change its flow field and aerodynamic characteristics. When convex modifications are applied, as the degree of convexity on the plate increases, the average drag coefficient gradually decreases, while the fluctuating lift coefficient initially decreases, then increases, and finally decreases again. The Strouhal number shows a gradual increase. After convex modification, both the average drag coefficient and the fluctuating lift coefficient of the plate are lower than the baseline values of the rectangular plate. When the ratio of the protrusion height to the plate width (H*/D) is 0.15, the fluctuating lift coefficient of the convex plate reaches its minimum value of approximately 0.005, representing a 99.2% reduction compared to the rectangular plate and nearly completely suppressing lift fluctuations. When concave modifications are applied, as the degree of concavity on the plate increases, both the average drag coefficient and the fluctuating lift coefficient initially increase and then decrease. However, the Strouhal number does not show significant changes. After concave modification, both the average drag coefficient and the fluctuating lift coefficient of the plate are higher than the corresponding values for the rectangular plate. The average drag coefficient peaks at 1.278 when the ratio of concave height to plate width is 0.25, representing a 20.2% increase. The fluctuating lift coefficient peaks at 1.273 when the ratio of concave height to plate width is 0.35, showing a 102% increase.